1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565 1566 1567 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622 1623
//! Spans represent periods of time in which a program was executing in a
//! particular context.
//!
//! A span consists of [fields], user-defined key-value pairs of arbitrary data
//! that describe the context the span represents, and a set of fixed attributes
//! that describe all `tracing` spans and events. Attributes describing spans
//! include:
//!
//! - An [`Id`] assigned by the subscriber that uniquely identifies it in relation
//! to other spans.
//! - The span's [parent] in the trace tree.
//! - [Metadata] that describes static characteristics of all spans
//! originating from that callsite, such as its name, source code location,
//! [verbosity level], and the names of its fields.
//!
//! # Creating Spans
//!
//! Spans are created using the [`span!`] macro. This macro is invoked with the
//! following arguments, in order:
//!
//! - The [`target`] and/or [`parent`][parent] attributes, if the user wishes to
//! override their default values.
//! - The span's [verbosity level]
//! - A string literal providing the span's name.
//! - Finally, zero or more arbitrary key/value fields.
//!
//! [`target`]: super::Metadata::target
//!
//! For example:
//! ```rust
//! use tracing::{span, Level};
//!
//! /// Construct a new span at the `INFO` level named "my_span", with a single
//! /// field named answer , with the value `42`.
//! let my_span = span!(Level::INFO, "my_span", answer = 42);
//! ```
//!
//! The documentation for the [`span!`] macro provides additional examples of
//! the various options that exist when creating spans.
//!
//! The [`trace_span!`], [`debug_span!`], [`info_span!`], [`warn_span!`], and
//! [`error_span!`] exist as shorthand for constructing spans at various
//! verbosity levels.
//!
//! ## Recording Span Creation
//!
//! The [`Attributes`] type contains data associated with a span, and is
//! provided to the [`Subscriber`] when a new span is created. It contains
//! the span's metadata, the ID of [the span's parent][parent] if one was
//! explicitly set, and any fields whose values were recorded when the span was
//! constructed. The subscriber, which is responsible for recording `tracing`
//! data, can then store or record these values.
//!
//! # The Span Lifecycle
//!
//! ## Entering a Span
//!
//! A thread of execution is said to _enter_ a span when it begins executing,
//! and _exit_ the span when it switches to another context. Spans may be
//! entered through the [`enter`], [`entered`], and [`in_scope`] methods.
//!
//! The [`enter`] method enters a span, returning a [guard] that exits the span
//! when dropped
//! ```
//! # use tracing::{span, Level};
//! let my_var: u64 = 5;
//! let my_span = span!(Level::TRACE, "my_span", my_var);
//!
//! // `my_span` exists but has not been entered.
//!
//! // Enter `my_span`...
//! let _enter = my_span.enter();
//!
//! // Perform some work inside of the context of `my_span`...
//! // Dropping the `_enter` guard will exit the span.
//!```
//!
//! <div class="example-wrap" style="display:inline-block"><pre class="compile_fail" style="white-space:normal;font:inherit;">
//! <strong>Warning</strong>: In asynchronous code that uses async/await syntax,
//! <code>Span::enter</code> may produce incorrect traces if the returned drop
//! guard is held across an await point. See
//! <a href="struct.Span.html#in-asynchronous-code">the method documentation</a>
//! for details.
//! </pre></div>
//!
//! The [`entered`] method is analogous to [`enter`], but moves the span into
//! the returned guard, rather than borrowing it. This allows creating and
//! entering a span in a single expression:
//!
//! ```
//! # use tracing::{span, Level};
//! // Create a span and enter it, returning a guard:
//! let span = span!(Level::INFO, "my_span").entered();
//!
//! // We are now inside the span! Like `enter()`, the guard returned by
//! // `entered()` will exit the span when it is dropped...
//!
//! // ...but, it can also be exited explicitly, returning the `Span`
//! // struct:
//! let span = span.exit();
//! ```
//!
//! Finally, [`in_scope`] takes a closure or function pointer and executes it
//! inside the span:
//!
//! ```
//! # use tracing::{span, Level};
//! let my_var: u64 = 5;
//! let my_span = span!(Level::TRACE, "my_span", my_var = &my_var);
//!
//! my_span.in_scope(|| {
//! // perform some work in the context of `my_span`...
//! });
//!
//! // Perform some work outside of the context of `my_span`...
//!
//! my_span.in_scope(|| {
//! // Perform some more work in the context of `my_span`.
//! });
//! ```
//!
//! <pre class="ignore" style="white-space:normal;font:inherit;">
//! <strong>Note</strong>: Since entering a span takes <code>&self</code>, and
//! <code>Span</code>s are <code>Clone</code>, <code>Send</code>, and
//! <code>Sync</code>, it is entirely valid for multiple threads to enter the
//! same span concurrently.
//! </pre>
//!
//! ## Span Relationships
//!
//! Spans form a tree structure — unless it is a root span, all spans have a
//! _parent_, and may have one or more _children_. When a new span is created,
//! the current span becomes the new span's parent. The total execution time of
//! a span consists of the time spent in that span and in the entire subtree
//! represented by its children. Thus, a parent span always lasts for at least
//! as long as the longest-executing span in its subtree.
//!
//! ```
//! # use tracing::{Level, span};
//! // this span is considered the "root" of a new trace tree:
//! span!(Level::INFO, "root").in_scope(|| {
//! // since we are now inside "root", this span is considered a child
//! // of "root":
//! span!(Level::DEBUG, "outer_child").in_scope(|| {
//! // this span is a child of "outer_child", which is in turn a
//! // child of "root":
//! span!(Level::TRACE, "inner_child").in_scope(|| {
//! // and so on...
//! });
//! });
//! // another span created here would also be a child of "root".
//! });
//!```
//!
//! In addition, the parent of a span may be explicitly specified in
//! the `span!` macro. For example:
//!
//! ```rust
//! # use tracing::{Level, span};
//! // Create, but do not enter, a span called "foo".
//! let foo = span!(Level::INFO, "foo");
//!
//! // Create and enter a span called "bar".
//! let bar = span!(Level::INFO, "bar");
//! let _enter = bar.enter();
//!
//! // Although we have currently entered "bar", "baz"'s parent span
//! // will be "foo".
//! let baz = span!(parent: &foo, Level::INFO, "baz");
//! ```
//!
//! A child span should typically be considered _part_ of its parent. For
//! example, if a subscriber is recording the length of time spent in various
//! spans, it should generally include the time spent in a span's children as
//! part of that span's duration.
//!
//! In addition to having zero or one parent, a span may also _follow from_ any
//! number of other spans. This indicates a causal relationship between the span
//! and the spans that it follows from, but a follower is *not* typically
//! considered part of the duration of the span it follows. Unlike the parent, a
//! span may record that it follows from another span after it is created, using
//! the [`follows_from`] method.
//!
//! As an example, consider a listener task in a server. As the listener accepts
//! incoming connections, it spawns new tasks that handle those connections. We
//! might want to have a span representing the listener, and instrument each
//! spawned handler task with its own span. We would want our instrumentation to
//! record that the handler tasks were spawned as a result of the listener task.
//! However, we might not consider the handler tasks to be _part_ of the time
//! spent in the listener task, so we would not consider those spans children of
//! the listener span. Instead, we would record that the handler tasks follow
//! from the listener, recording the causal relationship but treating the spans
//! as separate durations.
//!
//! ## Closing Spans
//!
//! Execution may enter and exit a span multiple times before that span is
//! _closed_. Consider, for example, a future which has an associated
//! span and enters that span every time it is polled:
//! ```rust
//! # use std::future::Future;
//! # use std::task::{Context, Poll};
//! # use std::pin::Pin;
//! struct MyFuture {
//! // data
//! span: tracing::Span,
//! }
//!
//! impl Future for MyFuture {
//! type Output = ();
//!
//! fn poll(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Self::Output> {
//! let _enter = self.span.enter();
//! // Do actual future work...
//! # Poll::Ready(())
//! }
//! }
//! ```
//!
//! If this future was spawned on an executor, it might yield one or more times
//! before `poll` returns [`Poll::Ready`]. If the future were to yield, then
//! the executor would move on to poll the next future, which may _also_ enter
//! an associated span or series of spans. Therefore, it is valid for a span to
//! be entered repeatedly before it completes. Only the time when that span or
//! one of its children was the current span is considered to be time spent in
//! that span. A span which is not executing and has not yet been closed is said
//! to be _idle_.
//!
//! Because spans may be entered and exited multiple times before they close,
//! [`Subscriber`]s have separate trait methods which are called to notify them
//! of span exits and when span handles are dropped. When execution exits a
//! span, [`exit`] will always be called with that span's ID to notify the
//! subscriber that the span has been exited. When span handles are dropped, the
//! [`drop_span`] method is called with that span's ID. The subscriber may use
//! this to determine whether or not the span will be entered again.
//!
//! If there is only a single handle with the capacity to exit a span, dropping
//! that handle "closes" the span, since the capacity to enter it no longer
//! exists. For example:
//! ```
//! # use tracing::{Level, span};
//! {
//! span!(Level::TRACE, "my_span").in_scope(|| {
//! // perform some work in the context of `my_span`...
//! }); // --> Subscriber::exit(my_span)
//!
//! // The handle to `my_span` only lives inside of this block; when it is
//! // dropped, the subscriber will be informed via `drop_span`.
//!
//! } // --> Subscriber::drop_span(my_span)
//! ```
//!
//! However, if multiple handles exist, the span can still be re-entered even if
//! one or more is dropped. For determining when _all_ handles to a span have
//! been dropped, `Subscriber`s have a [`clone_span`] method, which is called
//! every time a span handle is cloned. Combined with `drop_span`, this may be
//! used to track the number of handles to a given span — if `drop_span` has
//! been called one more time than the number of calls to `clone_span` for a
//! given ID, then no more handles to the span with that ID exist. The
//! subscriber may then treat it as closed.
//!
//! # When to use spans
//!
//! As a rule of thumb, spans should be used to represent discrete units of work
//! (e.g., a given request's lifetime in a server) or periods of time spent in a
//! given context (e.g., time spent interacting with an instance of an external
//! system, such as a database).
//!
//! Which scopes in a program correspond to new spans depend somewhat on user
//! intent. For example, consider the case of a loop in a program. Should we
//! construct one span and perform the entire loop inside of that span, like:
//!
//! ```rust
//! # use tracing::{Level, span};
//! # let n = 1;
//! let span = span!(Level::TRACE, "my_loop");
//! let _enter = span.enter();
//! for i in 0..n {
//! # let _ = i;
//! // ...
//! }
//! ```
//! Or, should we create a new span for each iteration of the loop, as in:
//! ```rust
//! # use tracing::{Level, span};
//! # let n = 1u64;
//! for i in 0..n {
//! let span = span!(Level::TRACE, "my_loop", iteration = i);
//! let _enter = span.enter();
//! // ...
//! }
//! ```
//!
//! Depending on the circumstances, we might want to do either, or both. For
//! example, if we want to know how long was spent in the loop overall, we would
//! create a single span around the entire loop; whereas if we wanted to know how
//! much time was spent in each individual iteration, we would enter a new span
//! on every iteration.
//!
//! [fields]: super::field
//! [Metadata]: super::Metadata
//! [verbosity level]: super::Level
//! [`Poll::Ready`]: std::task::Poll::Ready
//! [`span!`]: super::span!
//! [`trace_span!`]: super::trace_span!
//! [`debug_span!`]: super::debug_span!
//! [`info_span!`]: super::info_span!
//! [`warn_span!`]: super::warn_span!
//! [`error_span!`]: super::error_span!
//! [`clone_span`]: super::subscriber::Subscriber::clone_span()
//! [`drop_span`]: super::subscriber::Subscriber::drop_span()
//! [`exit`]: super::subscriber::Subscriber::exit
//! [`Subscriber`]: super::subscriber::Subscriber
//! [`enter`]: Span::enter()
//! [`entered`]: Span::entered()
//! [`in_scope`]: Span::in_scope()
//! [`follows_from`]: Span::follows_from()
//! [guard]: Entered
//! [parent]: #span-relationships
pub use tracing_core::span::{Attributes, Id, Record};
use crate::stdlib::{
cmp, fmt,
hash::{Hash, Hasher},
marker::PhantomData,
mem,
ops::Deref,
};
use crate::{
dispatcher::{self, Dispatch},
field, Metadata,
};
/// Trait implemented by types which have a span `Id`.
pub trait AsId: crate::sealed::Sealed {
/// Returns the `Id` of the span that `self` corresponds to, or `None` if
/// this corresponds to a disabled span.
fn as_id(&self) -> Option<&Id>;
}
/// A handle representing a span, with the capability to enter the span if it
/// exists.
///
/// If the span was rejected by the current `Subscriber`'s filter, entering the
/// span will silently do nothing. Thus, the handle can be used in the same
/// manner regardless of whether or not the trace is currently being collected.
#[derive(Clone)]
pub struct Span {
/// A handle used to enter the span when it is not executing.
///
/// If this is `None`, then the span has either closed or was never enabled.
inner: Option<Inner>,
/// Metadata describing the span.
///
/// This might be `Some` even if `inner` is `None`, in the case that the
/// span is disabled but the metadata is needed for `log` support.
meta: Option<&'static Metadata<'static>>,
}
/// A handle representing the capacity to enter a span which is known to exist.
///
/// Unlike `Span`, this type is only constructed for spans which _have_ been
/// enabled by the current filter. This type is primarily used for implementing
/// span handles; users should typically not need to interact with it directly.
#[derive(Debug)]
pub(crate) struct Inner {
/// The span's ID, as provided by `subscriber`.
id: Id,
/// The subscriber that will receive events relating to this span.
///
/// This should be the same subscriber that provided this span with its
/// `id`.
subscriber: Dispatch,
}
/// A guard representing a span which has been entered and is currently
/// executing.
///
/// When the guard is dropped, the span will be exited.
///
/// This is returned by the [`Span::enter`] function.
///
/// [`Span::enter`]: super::Span::enter
#[derive(Debug)]
#[must_use = "once a span has been entered, it should be exited"]
pub struct Entered<'a> {
span: &'a Span,
}
/// An owned version of [`Entered`], a guard representing a span which has been
/// entered and is currently executing.
///
/// When the guard is dropped, the span will be exited.
///
/// This is returned by the [`Span::entered`] function.
///
/// [`Span::entered`]: super::Span::entered()
#[derive(Debug)]
#[must_use = "once a span has been entered, it should be exited"]
pub struct EnteredSpan {
span: Span,
/// ```compile_fail
/// use tracing::span::*;
/// trait AssertSend: Send {}
///
/// impl AssertSend for EnteredSpan {}
/// ```
_not_send: PhantomNotSend,
}
/// `log` target for all span lifecycle (creation/enter/exit/close) records.
#[cfg(feature = "log")]
const LIFECYCLE_LOG_TARGET: &str = "tracing::span";
/// `log` target for span activity (enter/exit) records.
#[cfg(feature = "log")]
const ACTIVITY_LOG_TARGET: &str = "tracing::span::active";
// ===== impl Span =====
impl Span {
/// Constructs a new `Span` with the given [metadata] and set of
/// [field values].
///
/// The new span will be constructed by the currently-active [`Subscriber`],
/// with the current span as its parent (if one exists).
///
/// After the span is constructed, [field values] and/or [`follows_from`]
/// annotations may be added to it.
///
/// [metadata]: super::Metadata
/// [`Subscriber`]: super::subscriber::Subscriber
/// [field values]: super::field::ValueSet
/// [`follows_from`]: super::Span::follows_from
pub fn new(meta: &'static Metadata<'static>, values: &field::ValueSet<'_>) -> Span {
dispatcher::get_default(|dispatch| Self::new_with(meta, values, dispatch))
}
#[inline]
#[doc(hidden)]
pub fn new_with(
meta: &'static Metadata<'static>,
values: &field::ValueSet<'_>,
dispatch: &Dispatch,
) -> Span {
let new_span = Attributes::new(meta, values);
Self::make_with(meta, new_span, dispatch)
}
/// Constructs a new `Span` as the root of its own trace tree, with the
/// given [metadata] and set of [field values].
///
/// After the span is constructed, [field values] and/or [`follows_from`]
/// annotations may be added to it.
///
/// [metadata]: super::Metadata
/// [field values]: super::field::ValueSet
/// [`follows_from`]: super::Span::follows_from
pub fn new_root(meta: &'static Metadata<'static>, values: &field::ValueSet<'_>) -> Span {
dispatcher::get_default(|dispatch| Self::new_root_with(meta, values, dispatch))
}
#[inline]
#[doc(hidden)]
pub fn new_root_with(
meta: &'static Metadata<'static>,
values: &field::ValueSet<'_>,
dispatch: &Dispatch,
) -> Span {
let new_span = Attributes::new_root(meta, values);
Self::make_with(meta, new_span, dispatch)
}
/// Constructs a new `Span` as child of the given parent span, with the
/// given [metadata] and set of [field values].
///
/// After the span is constructed, [field values] and/or [`follows_from`]
/// annotations may be added to it.
///
/// [metadata]: super::Metadata
/// [field values]: super::field::ValueSet
/// [`follows_from`]: super::Span::follows_from
pub fn child_of(
parent: impl Into<Option<Id>>,
meta: &'static Metadata<'static>,
values: &field::ValueSet<'_>,
) -> Span {
let mut parent = parent.into();
dispatcher::get_default(move |dispatch| {
Self::child_of_with(Option::take(&mut parent), meta, values, dispatch)
})
}
#[inline]
#[doc(hidden)]
pub fn child_of_with(
parent: impl Into<Option<Id>>,
meta: &'static Metadata<'static>,
values: &field::ValueSet<'_>,
dispatch: &Dispatch,
) -> Span {
let new_span = match parent.into() {
Some(parent) => Attributes::child_of(parent, meta, values),
None => Attributes::new_root(meta, values),
};
Self::make_with(meta, new_span, dispatch)
}
/// Constructs a new disabled span with the given `Metadata`.
///
/// This should be used when a span is constructed from a known callsite,
/// but the subscriber indicates that it is disabled.
///
/// Entering, exiting, and recording values on this span will not notify the
/// `Subscriber` but _may_ record log messages if the `log` feature flag is
/// enabled.
#[inline(always)]
pub fn new_disabled(meta: &'static Metadata<'static>) -> Span {
Self {
inner: None,
meta: Some(meta),
}
}
/// Constructs a new span that is *completely disabled*.
///
/// This can be used rather than `Option<Span>` to represent cases where a
/// span is not present.
///
/// Entering, exiting, and recording values on this span will do nothing.
#[inline(always)]
pub const fn none() -> Span {
Self {
inner: None,
meta: None,
}
}
/// Returns a handle to the span [considered by the `Subscriber`] to be the
/// current span.
///
/// If the subscriber indicates that it does not track the current span, or
/// that the thread from which this function is called is not currently
/// inside a span, the returned span will be disabled.
///
/// [considered by the `Subscriber`]:
/// super::subscriber::Subscriber::current_span
pub fn current() -> Span {
dispatcher::get_default(|dispatch| {
if let Some((id, meta)) = dispatch.current_span().into_inner() {
let id = dispatch.clone_span(&id);
Self {
inner: Some(Inner::new(id, dispatch)),
meta: Some(meta),
}
} else {
Self::none()
}
})
}
fn make_with(
meta: &'static Metadata<'static>,
new_span: Attributes<'_>,
dispatch: &Dispatch,
) -> Span {
let attrs = &new_span;
let id = dispatch.new_span(attrs);
let inner = Some(Inner::new(id, dispatch));
let span = Self {
inner,
meta: Some(meta),
};
if_log_enabled! { *meta.level(), {
let target = if attrs.is_empty() {
LIFECYCLE_LOG_TARGET
} else {
meta.target()
};
let values = attrs.values();
span.log(
target,
level_to_log!(*meta.level()),
format_args!("++ {};{}", meta.name(), crate::log::LogValueSet { values, is_first: false }),
);
}}
span
}
/// Enters this span, returning a guard that will exit the span when dropped.
///
/// If this span is enabled by the current subscriber, then this function will
/// call [`Subscriber::enter`] with the span's [`Id`], and dropping the guard
/// will call [`Subscriber::exit`]. If the span is disabled, this does
/// nothing.
///
/// # In Asynchronous Code
///
/// **Warning**: in asynchronous code that uses [async/await syntax][syntax],
/// `Span::enter` should be used very carefully or avoided entirely. Holding
/// the drop guard returned by `Span::enter` across `.await` points will
/// result in incorrect traces. For example,
///
/// ```
/// # use tracing::info_span;
/// # async fn some_other_async_function() {}
/// async fn my_async_function() {
/// let span = info_span!("my_async_function");
///
/// // WARNING: This span will remain entered until this
/// // guard is dropped...
/// let _enter = span.enter();
/// // ...but the `await` keyword may yield, causing the
/// // runtime to switch to another task, while remaining in
/// // this span!
/// some_other_async_function().await
///
/// // ...
/// }
/// ```
///
/// The drop guard returned by `Span::enter` exits the span when it is
/// dropped. When an async function or async block yields at an `.await`
/// point, the current scope is _exited_, but values in that scope are
/// **not** dropped (because the async block will eventually resume
/// execution from that await point). This means that _another_ task will
/// begin executing while _remaining_ in the entered span. This results in
/// an incorrect trace.
///
/// Instead of using `Span::enter` in asynchronous code, prefer the
/// following:
///
/// * To enter a span for a synchronous section of code within an async
/// block or function, prefer [`Span::in_scope`]. Since `in_scope` takes a
/// synchronous closure and exits the span when the closure returns, the
/// span will always be exited before the next await point. For example:
/// ```
/// # use tracing::info_span;
/// # async fn some_other_async_function(_: ()) {}
/// async fn my_async_function() {
/// let span = info_span!("my_async_function");
///
/// let some_value = span.in_scope(|| {
/// // run some synchronous code inside the span...
/// });
///
/// // This is okay! The span has already been exited before we reach
/// // the await point.
/// some_other_async_function(some_value).await;
///
/// // ...
/// }
/// ```
/// * For instrumenting asynchronous code, `tracing` provides the
/// [`Future::instrument` combinator][instrument] for
/// attaching a span to a future (async function or block). This will
/// enter the span _every_ time the future is polled, and exit it whenever
/// the future yields.
///
/// `Instrument` can be used with an async block inside an async function:
/// ```ignore
/// # use tracing::info_span;
/// use tracing::Instrument;
///
/// # async fn some_other_async_function() {}
/// async fn my_async_function() {
/// let span = info_span!("my_async_function");
/// async move {
/// // This is correct! If we yield here, the span will be exited,
/// // and re-entered when we resume.
/// some_other_async_function().await;
///
/// //more asynchronous code inside the span...
///
/// }
/// // instrument the async block with the span...
/// .instrument(span)
/// // ...and await it.
/// .await
/// }
/// ```
///
/// It can also be used to instrument calls to async functions at the
/// callsite:
/// ```ignore
/// # use tracing::debug_span;
/// use tracing::Instrument;
///
/// # async fn some_other_async_function() {}
/// async fn my_async_function() {
/// let some_value = some_other_async_function()
/// .instrument(debug_span!("some_other_async_function"))
/// .await;
///
/// // ...
/// }
/// ```
///
/// * The [`#[instrument]` attribute macro][attr] can automatically generate
/// correct code when used on an async function:
///
/// ```ignore
/// # async fn some_other_async_function() {}
/// #[tracing::instrument(level = "info")]
/// async fn my_async_function() {
///
/// // This is correct! If we yield here, the span will be exited,
/// // and re-entered when we resume.
/// some_other_async_function().await;
///
/// // ...
///
/// }
/// ```
///
/// [syntax]: https://rust-lang.github.io/async-book/01_getting_started/04_async_await_primer.html
/// [`Span::in_scope`]: Span::in_scope()
/// [instrument]: crate::Instrument
/// [attr]: macro@crate::instrument
///
/// # Examples
///
/// ```
/// # use tracing::{span, Level};
/// let span = span!(Level::INFO, "my_span");
/// let guard = span.enter();
///
/// // code here is within the span
///
/// drop(guard);
///
/// // code here is no longer within the span
///
/// ```
///
/// Guards need not be explicitly dropped:
///
/// ```
/// # use tracing::trace_span;
/// fn my_function() -> String {
/// // enter a span for the duration of this function.
/// let span = trace_span!("my_function");
/// let _enter = span.enter();
///
/// // anything happening in functions we call is still inside the span...
/// my_other_function();
///
/// // returning from the function drops the guard, exiting the span.
/// return "Hello world".to_owned();
/// }
///
/// fn my_other_function() {
/// // ...
/// }
/// ```
///
/// Sub-scopes may be created to limit the duration for which the span is
/// entered:
///
/// ```
/// # use tracing::{info, info_span};
/// let span = info_span!("my_great_span");
///
/// {
/// let _enter = span.enter();
///
/// // this event occurs inside the span.
/// info!("i'm in the span!");
///
/// // exiting the scope drops the guard, exiting the span.
/// }
///
/// // this event is not inside the span.
/// info!("i'm outside the span!")
/// ```
///
/// [`Subscriber::enter`]: super::subscriber::Subscriber::enter()
/// [`Subscriber::exit`]: super::subscriber::Subscriber::exit()
/// [`Id`]: super::Id
#[inline(always)]
pub fn enter(&self) -> Entered<'_> {
self.do_enter();
Entered { span: self }
}
/// Enters this span, consuming it and returning a [guard][`EnteredSpan`]
/// that will exit the span when dropped.
///
/// <pre class="compile_fail" style="white-space:normal;font:inherit;">
/// <strong>Warning</strong>: In asynchronous code that uses async/await syntax,
/// <code>Span::entered</code> may produce incorrect traces if the returned drop
/// guard is held across an await point. See <a href="#in-asynchronous-code">the
/// <code>Span::enter</code> documentation</a> for details.
/// </pre>
///
///
/// If this span is enabled by the current subscriber, then this function will
/// call [`Subscriber::enter`] with the span's [`Id`], and dropping the guard
/// will call [`Subscriber::exit`]. If the span is disabled, this does
/// nothing.
///
/// This is similar to the [`Span::enter`] method, except that it moves the
/// span by value into the returned guard, rather than borrowing it.
/// Therefore, this method can be used to create and enter a span in a
/// single expression, without requiring a `let`-binding. For example:
///
/// ```
/// # use tracing::info_span;
/// let _span = info_span!("something_interesting").entered();
/// ```
/// rather than:
/// ```
/// # use tracing::info_span;
/// let span = info_span!("something_interesting");
/// let _e = span.enter();
/// ```
///
/// Furthermore, `entered` may be used when the span must be stored in some
/// other struct or be passed to a function while remaining entered.
///
/// <pre class="ignore" style="white-space:normal;font:inherit;">
/// <strong>Note</strong>: The returned <a href="../struct.EnteredSpan.html">
/// <code>EnteredSpan</code></a> guard does not implement <code>Send</code>.
/// Dropping the guard will exit <em>this</em> span, and if the guard is sent
/// to another thread and dropped there, that thread may never have entered
/// this span. Thus, <code>EnteredSpan</code>s should not be sent between threads.
/// </pre>
///
/// [syntax]: https://rust-lang.github.io/async-book/01_getting_started/04_async_await_primer.html
///
/// # Examples
///
/// The returned guard can be [explicitly exited][EnteredSpan::exit],
/// returning the un-entered span:
///
/// ```
/// # use tracing::{Level, span};
/// let span = span!(Level::INFO, "doing_something").entered();
///
/// // code here is within the span
///
/// // explicitly exit the span, returning it
/// let span = span.exit();
///
/// // code here is no longer within the span
///
/// // enter the span again
/// let span = span.entered();
///
/// // now we are inside the span once again
/// ```
///
/// Guards need not be explicitly dropped:
///
/// ```
/// # use tracing::trace_span;
/// fn my_function() -> String {
/// // enter a span for the duration of this function.
/// let span = trace_span!("my_function").entered();
///
/// // anything happening in functions we call is still inside the span...
/// my_other_function();
///
/// // returning from the function drops the guard, exiting the span.
/// return "Hello world".to_owned();
/// }
///
/// fn my_other_function() {
/// // ...
/// }
/// ```
///
/// Since the [`EnteredSpan`] guard can dereference to the [`Span`] itself,
/// the span may still be accessed while entered. For example:
///
/// ```rust
/// # use tracing::info_span;
/// use tracing::field;
///
/// // create the span with an empty field, and enter it.
/// let span = info_span!("my_span", some_field = field::Empty).entered();
///
/// // we can still record a value for the field while the span is entered.
/// span.record("some_field", &"hello world!");
/// ```
///
/// [`Subscriber::enter`]: super::subscriber::Subscriber::enter()
/// [`Subscriber::exit`]: super::subscriber::Subscriber::exit()
/// [`Id`]: super::Id
#[inline(always)]
pub fn entered(self) -> EnteredSpan {
self.do_enter();
EnteredSpan {
span: self,
_not_send: PhantomNotSend,
}
}
/// Returns this span, if it was [enabled] by the current [`Subscriber`], or
/// the [current span] (whose lexical distance may be further than expected),
/// if this span [is disabled].
///
/// This method can be useful when propagating spans to spawned threads or
/// [async tasks]. Consider the following:
///
/// ```
/// let _parent_span = tracing::info_span!("parent").entered();
///
/// // ...
///
/// let child_span = tracing::debug_span!("child");
///
/// std::thread::spawn(move || {
/// let _entered = child_span.entered();
///
/// tracing::info!("spawned a thread!");
///
/// // ...
/// });
/// ```
///
/// If the current [`Subscriber`] enables the [`DEBUG`] level, then both
/// the "parent" and "child" spans will be enabled. Thus, when the "spawaned
/// a thread!" event occurs, it will be inside of the "child" span. Because
/// "parent" is the parent of "child", the event will _also_ be inside of
/// "parent".
///
/// However, if the [`Subscriber`] only enables the [`INFO`] level, the "child"
/// span will be disabled. When the thread is spawned, the
/// `child_span.entered()` call will do nothing, since "child" is not
/// enabled. In this case, the "spawned a thread!" event occurs outside of
/// *any* span, since the "child" span was responsible for propagating its
/// parent to the spawned thread.
///
/// If this is not the desired behavior, `Span::or_current` can be used to
/// ensure that the "parent" span is propagated in both cases, either as a
/// parent of "child" _or_ directly. For example:
///
/// ```
/// let _parent_span = tracing::info_span!("parent").entered();
///
/// // ...
///
/// // If DEBUG is enabled, then "child" will be enabled, and `or_current`
/// // returns "child". Otherwise, if DEBUG is not enabled, "child" will be
/// // disabled, and `or_current` returns "parent".
/// let child_span = tracing::debug_span!("child").or_current();
///
/// std::thread::spawn(move || {
/// let _entered = child_span.entered();
///
/// tracing::info!("spawned a thread!");
///
/// // ...
/// });
/// ```
///
/// When spawning [asynchronous tasks][async tasks], `Span::or_current` can
/// be used similarly, in combination with [`instrument`]:
///
/// ```
/// use tracing::Instrument;
/// # // lol
/// # mod tokio {
/// # pub(super) fn spawn(_: impl std::future::Future) {}
/// # }
///
/// let _parent_span = tracing::info_span!("parent").entered();
///
/// // ...
///
/// let child_span = tracing::debug_span!("child");
///
/// tokio::spawn(
/// async {
/// tracing::info!("spawned a task!");
///
/// // ...
///
/// }.instrument(child_span.or_current())
/// );
/// ```
///
/// In general, `or_current` should be preferred over nesting an
/// [`instrument`] call inside of an [`in_current_span`] call, as using
/// `or_current` will be more efficient.
///
/// ```
/// use tracing::Instrument;
/// # // lol
/// # mod tokio {
/// # pub(super) fn spawn(_: impl std::future::Future) {}
/// # }
/// async fn my_async_fn() {
/// // ...
/// }
///
/// let _parent_span = tracing::info_span!("parent").entered();
///
/// // Do this:
/// tokio::spawn(
/// my_async_fn().instrument(tracing::debug_span!("child").or_current())
/// );
///
/// // ...rather than this:
/// tokio::spawn(
/// my_async_fn()
/// .instrument(tracing::debug_span!("child"))
/// .in_current_span()
/// );
/// ```
///
/// [enabled]: crate::Subscriber::enabled
/// [`Subscriber`]: crate::Subscriber
/// [current span]: Span::current
/// [is disabled]: Span::is_disabled
/// [`INFO`]: crate::Level::INFO
/// [`DEBUG`]: crate::Level::DEBUG
/// [async tasks]: std::task
/// [`instrument`]: crate::instrument::Instrument::instrument
/// [`in_current_span`]: crate::instrument::Instrument::in_current_span
pub fn or_current(self) -> Self {
if self.is_disabled() {
return Self::current();
}
self
}
#[inline(always)]
fn do_enter(&self) {
if let Some(inner) = self.inner.as_ref() {
inner.subscriber.enter(&inner.id);
}
if_log_enabled! { crate::Level::TRACE, {
if let Some(_meta) = self.meta {
self.log(ACTIVITY_LOG_TARGET, log::Level::Trace, format_args!("-> {};", _meta.name()));
}
}}
}
// Called from [`Entered`] and [`EnteredSpan`] drops.
//
// Running this behaviour on drop rather than with an explicit function
// call means that spans may still be exited when unwinding.
#[inline(always)]
fn do_exit(&self) {
if let Some(inner) = self.inner.as_ref() {
inner.subscriber.exit(&inner.id);
}
if_log_enabled! { crate::Level::TRACE, {
if let Some(_meta) = self.meta {
self.log(ACTIVITY_LOG_TARGET, log::Level::Trace, format_args!("<- {};", _meta.name()));
}
}}
}
/// Executes the given function in the context of this span.
///
/// If this span is enabled, then this function enters the span, invokes `f`
/// and then exits the span. If the span is disabled, `f` will still be
/// invoked, but in the context of the currently-executing span (if there is
/// one).
///
/// Returns the result of evaluating `f`.
///
/// # Examples
///
/// ```
/// # use tracing::{trace, span, Level};
/// let my_span = span!(Level::TRACE, "my_span");
///
/// my_span.in_scope(|| {
/// // this event occurs within the span.
/// trace!("i'm in the span!");
/// });
///
/// // this event occurs outside the span.
/// trace!("i'm not in the span!");
/// ```
///
/// Calling a function and returning the result:
/// ```
/// # use tracing::{info_span, Level};
/// fn hello_world() -> String {
/// "Hello world!".to_owned()
/// }
///
/// let span = info_span!("hello_world");
/// // the span will be entered for the duration of the call to
/// // `hello_world`.
/// let a_string = span.in_scope(hello_world);
///
pub fn in_scope<F: FnOnce() -> T, T>(&self, f: F) -> T {
let _enter = self.enter();
f()
}
/// Returns a [`Field`][super::field::Field] for the field with the
/// given `name`, if one exists,
pub fn field<Q: ?Sized>(&self, field: &Q) -> Option<field::Field>
where
Q: field::AsField,
{
self.metadata().and_then(|meta| field.as_field(meta))
}
/// Returns true if this `Span` has a field for the given
/// [`Field`][super::field::Field] or field name.
#[inline]
pub fn has_field<Q: ?Sized>(&self, field: &Q) -> bool
where
Q: field::AsField,
{
self.field(field).is_some()
}
/// Records that the field described by `field` has the value `value`.
///
/// This may be used with [`field::Empty`] to declare fields whose values
/// are not known when the span is created, and record them later:
/// ```
/// use tracing::{trace_span, field};
///
/// // Create a span with two fields: `greeting`, with the value "hello world", and
/// // `parting`, without a value.
/// let span = trace_span!("my_span", greeting = "hello world", parting = field::Empty);
///
/// // ...
///
/// // Now, record a value for parting as well.
/// // (note that the field name is passed as a string slice)
/// span.record("parting", "goodbye world!");
/// ```
/// However, it may also be used to record a _new_ value for a field whose
/// value was already recorded:
/// ```
/// use tracing::info_span;
/// # fn do_something() -> Result<(), ()> { Err(()) }
///
/// // Initially, let's assume that our attempt to do something is going okay...
/// let span = info_span!("doing_something", is_okay = true);
/// let _e = span.enter();
///
/// match do_something() {
/// Ok(something) => {
/// // ...
/// }
/// Err(_) => {
/// // Things are no longer okay!
/// span.record("is_okay", false);
/// }
/// }
/// ```
///
/// <pre class="ignore" style="white-space:normal;font:inherit;">
/// <strong>Note</strong>: The fields associated with a span are part
/// of its <a href="../struct.Metadata.html"><code>Metadata</code></a>.
/// The <a href="../struct.Metadata.html"><code>Metadata</code></a>
/// describing a particular span is constructed statically when the span
/// is created and cannot be extended later to add new fields. Therefore,
/// you cannot record a value for a field that was not specified when the
/// span was created:
/// </pre>
///
/// ```
/// use tracing::{trace_span, field};
///
/// // Create a span with two fields: `greeting`, with the value "hello world", and
/// // `parting`, without a value.
/// let span = trace_span!("my_span", greeting = "hello world", parting = field::Empty);
///
/// // ...
///
/// // Now, you try to record a value for a new field, `new_field`, which was not
/// // declared as `Empty` or populated when you created `span`.
/// // You won't get any error, but the assignment will have no effect!
/// span.record("new_field", "interesting_value_you_really_need");
///
/// // Instead, all fields that may be recorded after span creation should be declared up front,
/// // using field::Empty when a value is not known, as we did for `parting`.
/// // This `record` call will indeed replace field::Empty with "you will be remembered".
/// span.record("parting", "you will be remembered");
/// ```
///
/// [`field::Empty`]: super::field::Empty
/// [`Metadata`]: super::Metadata
pub fn record<Q: ?Sized, V>(&self, field: &Q, value: V) -> &Self
where
Q: field::AsField,
V: field::Value,
{
if let Some(meta) = self.meta {
if let Some(field) = field.as_field(meta) {
self.record_all(
&meta
.fields()
.value_set(&[(&field, Some(&value as &dyn field::Value))]),
);
}
}
self
}
/// Records all the fields in the provided `ValueSet`.
pub fn record_all(&self, values: &field::ValueSet<'_>) -> &Self {
let record = Record::new(values);
if let Some(ref inner) = self.inner {
inner.record(&record);
}
if let Some(_meta) = self.meta {
if_log_enabled! { *_meta.level(), {
let target = if record.is_empty() {
LIFECYCLE_LOG_TARGET
} else {
_meta.target()
};
self.log(
target,
level_to_log!(*_meta.level()),
format_args!("{};{}", _meta.name(), crate::log::LogValueSet { values, is_first: false }),
);
}}
}
self
}
/// Returns `true` if this span was disabled by the subscriber and does not
/// exist.
///
/// See also [`is_none`].
///
/// [`is_none`]: Span::is_none()
#[inline]
pub fn is_disabled(&self) -> bool {
self.inner.is_none()
}
/// Returns `true` if this span was constructed by [`Span::none`] and is
/// empty.
///
/// If `is_none` returns `true` for a given span, then [`is_disabled`] will
/// also return `true`. However, when a span is disabled by the subscriber
/// rather than constructed by `Span::none`, this method will return
/// `false`, while `is_disabled` will return `true`.
///
/// [`Span::none`]: Span::none()
/// [`is_disabled`]: Span::is_disabled()
#[inline]
pub fn is_none(&self) -> bool {
self.is_disabled() && self.meta.is_none()
}
/// Indicates that the span with the given ID has an indirect causal
/// relationship with this span.
///
/// This relationship differs somewhat from the parent-child relationship: a
/// span may have any number of prior spans, rather than a single one; and
/// spans are not considered to be executing _inside_ of the spans they
/// follow from. This means that a span may close even if subsequent spans
/// that follow from it are still open, and time spent inside of a
/// subsequent span should not be included in the time its precedents were
/// executing. This is used to model causal relationships such as when a
/// single future spawns several related background tasks, et cetera.
///
/// If this span is disabled, or the resulting follows-from relationship
/// would be invalid, this function will do nothing.
///
/// # Examples
///
/// Setting a `follows_from` relationship with a `Span`:
/// ```
/// # use tracing::{span, Id, Level, Span};
/// let span1 = span!(Level::INFO, "span_1");
/// let span2 = span!(Level::DEBUG, "span_2");
/// span2.follows_from(span1);
/// ```
///
/// Setting a `follows_from` relationship with the current span:
/// ```
/// # use tracing::{span, Id, Level, Span};
/// let span = span!(Level::INFO, "hello!");
/// span.follows_from(Span::current());
/// ```
///
/// Setting a `follows_from` relationship with a `Span` reference:
/// ```
/// # use tracing::{span, Id, Level, Span};
/// let span = span!(Level::INFO, "hello!");
/// let curr = Span::current();
/// span.follows_from(&curr);
/// ```
///
/// Setting a `follows_from` relationship with an `Id`:
/// ```
/// # use tracing::{span, Id, Level, Span};
/// let span = span!(Level::INFO, "hello!");
/// let id = span.id();
/// span.follows_from(id);
/// ```
pub fn follows_from(&self, from: impl Into<Option<Id>>) -> &Self {
if let Some(ref inner) = self.inner {
if let Some(from) = from.into() {
inner.follows_from(&from);
}
}
self
}
/// Returns this span's `Id`, if it is enabled.
pub fn id(&self) -> Option<Id> {
self.inner.as_ref().map(Inner::id)
}
/// Returns this span's `Metadata`, if it is enabled.
pub fn metadata(&self) -> Option<&'static Metadata<'static>> {
self.meta
}
#[cfg(feature = "log")]
#[inline]
fn log(&self, target: &str, level: log::Level, message: fmt::Arguments<'_>) {
if let Some(meta) = self.meta {
if level_to_log!(*meta.level()) <= log::max_level() {
let logger = log::logger();
let log_meta = log::Metadata::builder().level(level).target(target).build();
if logger.enabled(&log_meta) {
if let Some(ref inner) = self.inner {
logger.log(
&log::Record::builder()
.metadata(log_meta)
.module_path(meta.module_path())
.file(meta.file())
.line(meta.line())
.args(format_args!("{} span={}", message, inner.id.into_u64()))
.build(),
);
} else {
logger.log(
&log::Record::builder()
.metadata(log_meta)
.module_path(meta.module_path())
.file(meta.file())
.line(meta.line())
.args(message)
.build(),
);
}
}
}
}
}
/// Invokes a function with a reference to this span's ID and subscriber.
///
/// if this span is enabled, the provided function is called, and the result is returned.
/// If the span is disabled, the function is not called, and this method returns `None`
/// instead.
pub fn with_subscriber<T>(&self, f: impl FnOnce((&Id, &Dispatch)) -> T) -> Option<T> {
self.inner
.as_ref()
.map(|inner| f((&inner.id, &inner.subscriber)))
}
}
impl cmp::PartialEq for Span {
fn eq(&self, other: &Self) -> bool {
match (&self.meta, &other.meta) {
(Some(this), Some(that)) => {
this.callsite() == that.callsite() && self.inner == other.inner
}
_ => false,
}
}
}
impl Hash for Span {
fn hash<H: Hasher>(&self, hasher: &mut H) {
self.inner.hash(hasher);
}
}
impl fmt::Debug for Span {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let mut span = f.debug_struct("Span");
if let Some(meta) = self.meta {
span.field("name", &meta.name())
.field("level", &meta.level())
.field("target", &meta.target());
if let Some(ref inner) = self.inner {
span.field("id", &inner.id());
} else {
span.field("disabled", &true);
}
if let Some(ref path) = meta.module_path() {
span.field("module_path", &path);
}
if let Some(ref line) = meta.line() {
span.field("line", &line);
}
if let Some(ref file) = meta.file() {
span.field("file", &file);
}
} else {
span.field("none", &true);
}
span.finish()
}
}
impl<'a> From<&'a Span> for Option<&'a Id> {
fn from(span: &'a Span) -> Self {
span.inner.as_ref().map(|inner| &inner.id)
}
}
impl<'a> From<&'a Span> for Option<Id> {
fn from(span: &'a Span) -> Self {
span.inner.as_ref().map(Inner::id)
}
}
impl From<Span> for Option<Id> {
fn from(span: Span) -> Self {
span.inner.as_ref().map(Inner::id)
}
}
impl<'a> From<&'a EnteredSpan> for Option<&'a Id> {
fn from(span: &'a EnteredSpan) -> Self {
span.inner.as_ref().map(|inner| &inner.id)
}
}
impl<'a> From<&'a EnteredSpan> for Option<Id> {
fn from(span: &'a EnteredSpan) -> Self {
span.inner.as_ref().map(Inner::id)
}
}
impl Drop for Span {
#[inline(always)]
fn drop(&mut self) {
if let Some(Inner {
ref id,
ref subscriber,
}) = self.inner
{
subscriber.try_close(id.clone());
}
if_log_enabled! { crate::Level::TRACE, {
if let Some(meta) = self.meta {
self.log(
LIFECYCLE_LOG_TARGET,
log::Level::Trace,
format_args!("-- {};", meta.name()),
);
}
}}
}
}
// ===== impl Inner =====
impl Inner {
/// Indicates that the span with the given ID has an indirect causal
/// relationship with this span.
///
/// This relationship differs somewhat from the parent-child relationship: a
/// span may have any number of prior spans, rather than a single one; and
/// spans are not considered to be executing _inside_ of the spans they
/// follow from. This means that a span may close even if subsequent spans
/// that follow from it are still open, and time spent inside of a
/// subsequent span should not be included in the time its precedents were
/// executing. This is used to model causal relationships such as when a
/// single future spawns several related background tasks, et cetera.
///
/// If this span is disabled, this function will do nothing. Otherwise, it
/// returns `Ok(())` if the other span was added as a precedent of this
/// span, or an error if this was not possible.
fn follows_from(&self, from: &Id) {
self.subscriber.record_follows_from(&self.id, from)
}
/// Returns the span's ID.
fn id(&self) -> Id {
self.id.clone()
}
fn record(&self, values: &Record<'_>) {
self.subscriber.record(&self.id, values)
}
fn new(id: Id, subscriber: &Dispatch) -> Self {
Inner {
id,
subscriber: subscriber.clone(),
}
}
}
impl cmp::PartialEq for Inner {
fn eq(&self, other: &Self) -> bool {
self.id == other.id
}
}
impl Hash for Inner {
fn hash<H: Hasher>(&self, state: &mut H) {
self.id.hash(state);
}
}
impl Clone for Inner {
fn clone(&self) -> Self {
Inner {
id: self.subscriber.clone_span(&self.id),
subscriber: self.subscriber.clone(),
}
}
}
// ===== impl Entered =====
impl EnteredSpan {
/// Returns this span's `Id`, if it is enabled.
pub fn id(&self) -> Option<Id> {
self.inner.as_ref().map(Inner::id)
}
/// Exits this span, returning the underlying [`Span`].
#[inline]
pub fn exit(mut self) -> Span {
// One does not simply move out of a struct with `Drop`.
let span = mem::replace(&mut self.span, Span::none());
span.do_exit();
span
}
}
impl Deref for EnteredSpan {
type Target = Span;
#[inline]
fn deref(&self) -> &Span {
&self.span
}
}
impl<'a> Drop for Entered<'a> {
#[inline(always)]
fn drop(&mut self) {
self.span.do_exit()
}
}
impl Drop for EnteredSpan {
#[inline(always)]
fn drop(&mut self) {
self.span.do_exit()
}
}
/// Technically, `EnteredSpan` _can_ implement both `Send` *and*
/// `Sync` safely. It doesn't, because it has a `PhantomNotSend` field,
/// specifically added in order to make it `!Send`.
///
/// Sending an `EnteredSpan` guard between threads cannot cause memory unsafety.
/// However, it *would* result in incorrect behavior, so we add a
/// `PhantomNotSend` to prevent it from being sent between threads. This is
/// because it must be *dropped* on the same thread that it was created;
/// otherwise, the span will never be exited on the thread where it was entered,
/// and it will attempt to exit the span on a thread that may never have entered
/// it. However, we still want them to be `Sync` so that a struct holding an
/// `Entered` guard can be `Sync`.
///
/// Thus, this is totally safe.
#[derive(Debug)]
struct PhantomNotSend {
ghost: PhantomData<*mut ()>,
}
#[allow(non_upper_case_globals)]
const PhantomNotSend: PhantomNotSend = PhantomNotSend { ghost: PhantomData };
/// # Safety
///
/// Trivially safe, as `PhantomNotSend` doesn't have any API.
unsafe impl Sync for PhantomNotSend {}
#[cfg(test)]
mod test {
use super::*;
trait AssertSend: Send {}
impl AssertSend for Span {}
trait AssertSync: Sync {}
impl AssertSync for Span {}
impl AssertSync for Entered<'_> {}
impl AssertSync for EnteredSpan {}
#[test]
fn test_record_backwards_compat() {
Span::current().record("some-key", "some text");
Span::current().record("some-key", false);
}
}