Source file src/runtime/time.go
1 // Copyright 2009 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 // Time-related runtime and pieces of package time. 6 7 package runtime 8 9 import ( 10 "internal/abi" 11 "internal/runtime/atomic" 12 "internal/runtime/sys" 13 "unsafe" 14 ) 15 16 //go:linkname time_runtimeNow time.runtimeNow 17 func time_runtimeNow() (sec int64, nsec int32, mono int64) { 18 if bubble := getg().bubble; bubble != nil { 19 sec = bubble.now / (1000 * 1000 * 1000) 20 nsec = int32(bubble.now % (1000 * 1000 * 1000)) 21 // Don't return a monotonic time inside a synctest bubble. 22 // If we return a monotonic time based on the fake clock, 23 // arithmetic on times created inside/outside bubbles is confusing. 24 // If we return a monotonic time based on the real monotonic clock, 25 // arithmetic on times created in the same bubble is confusing. 26 // Simplest is to omit the monotonic time within a bubble. 27 return sec, nsec, 0 28 } 29 return time_now() 30 } 31 32 //go:linkname time_runtimeNano time.runtimeNano 33 func time_runtimeNano() int64 { 34 gp := getg() 35 if gp.bubble != nil { 36 return gp.bubble.now 37 } 38 return nanotime() 39 } 40 41 //go:linkname time_runtimeIsBubbled time.runtimeIsBubbled 42 func time_runtimeIsBubbled() bool { 43 return getg().bubble != nil 44 } 45 46 // A timer is a potentially repeating trigger for calling t.f(t.arg, t.seq). 47 // Timers are allocated by client code, often as part of other data structures. 48 // Each P has a heap of pointers to timers that it manages. 49 // 50 // A timer is expected to be used by only one client goroutine at a time, 51 // but there will be concurrent access by the P managing that timer. 52 // Timer accesses are protected by the lock t.mu, with a snapshot of 53 // t's state bits published in t.astate to enable certain fast paths to make 54 // decisions about a timer without acquiring the lock. 55 type timer struct { 56 // mu protects reads and writes to all fields, with exceptions noted below. 57 mu mutex 58 59 astate atomic.Uint8 // atomic copy of state bits at last unlock 60 state uint8 // state bits 61 isChan bool // timer has a channel; immutable; can be read without lock 62 isFake bool // timer is using fake time; immutable; can be read without lock 63 64 blocked uint32 // number of goroutines blocked on timer's channel 65 rand uint32 // randomizes order of timers at same instant; only set when isFake 66 67 // Timer wakes up at when, and then at when+period, ... (period > 0 only) 68 // each time calling f(arg, seq, delay) in the timer goroutine, so f must be 69 // a well-behaved function and not block. 70 // 71 // The arg and seq are client-specified opaque arguments passed back to f. 72 // When used from netpoll, arg and seq have meanings defined by netpoll 73 // and are completely opaque to this code; in that context, seq is a sequence 74 // number to recognize and squelch stale function invocations. 75 // When used from package time, arg is a channel (for After, NewTicker) 76 // or the function to call (for AfterFunc) and seq is unused (0). 77 // 78 // Package time does not know about seq, but if this is a channel timer (t.isChan == true), 79 // this file uses t.seq as a sequence number to recognize and squelch 80 // sends that correspond to an earlier (stale) timer configuration, 81 // similar to its use in netpoll. In this usage (that is, when t.isChan == true), 82 // writes to seq are protected by both t.mu and t.sendLock, 83 // so reads are allowed when holding either of the two mutexes. 84 // 85 // The delay argument is nanotime() - t.when, meaning the delay in ns between 86 // when the timer should have gone off and now. Normally that amount is 87 // small enough not to matter, but for channel timers that are fed lazily, 88 // the delay can be arbitrarily long; package time subtracts it out to make 89 // it look like the send happened earlier than it actually did. 90 // (No one looked at the channel since then, or the send would have 91 // not happened so late, so no one can tell the difference.) 92 when int64 93 period int64 94 f func(arg any, seq uintptr, delay int64) 95 arg any 96 seq uintptr 97 98 // If non-nil, the timers containing t. 99 ts *timers 100 101 // sendLock protects sends on the timer's channel. 102 // Not used for async (pre-Go 1.23) behavior when debug.asynctimerchan.Load() != 0. 103 sendLock mutex 104 105 // isSending is used to handle races between running a 106 // channel timer and stopping or resetting the timer. 107 // It is used only for channel timers (t.isChan == true). 108 // It is not used for tickers. 109 // The value is incremented when about to send a value on the channel, 110 // and decremented after sending the value. 111 // The stop/reset code uses this to detect whether it 112 // stopped the channel send. 113 // 114 // isSending is incremented only when t.mu is held. 115 // isSending is decremented only when t.sendLock is held. 116 // isSending is read only when both t.mu and t.sendLock are held. 117 isSending atomic.Int32 118 } 119 120 // init initializes a newly allocated timer t. 121 // Any code that allocates a timer must call t.init before using it. 122 // The arg and f can be set during init, or they can be nil in init 123 // and set by a future call to t.modify. 124 func (t *timer) init(f func(arg any, seq uintptr, delay int64), arg any) { 125 lockInit(&t.mu, lockRankTimer) 126 t.f = f 127 t.arg = arg 128 } 129 130 // A timers is a per-P set of timers. 131 type timers struct { 132 // mu protects timers; timers are per-P, but the scheduler can 133 // access the timers of another P, so we have to lock. 134 mu mutex 135 136 // heap is the set of timers, ordered by heap[i].when. 137 // Must hold lock to access. 138 heap []timerWhen 139 140 // len is an atomic copy of len(heap). 141 len atomic.Uint32 142 143 // zombies is the number of timers in the heap 144 // that are marked for removal. 145 zombies atomic.Int32 146 147 // raceCtx is the race context used while executing timer functions. 148 raceCtx uintptr 149 150 // minWhenHeap is the minimum heap[i].when value (= heap[0].when). 151 // The wakeTime method uses minWhenHeap and minWhenModified 152 // to determine the next wake time. 153 // If minWhenHeap = 0, it means there are no timers in the heap. 154 minWhenHeap atomic.Int64 155 156 // minWhenModified is a lower bound on the minimum 157 // heap[i].when over timers with the timerModified bit set. 158 // If minWhenModified = 0, it means there are no timerModified timers in the heap. 159 minWhenModified atomic.Int64 160 } 161 162 type timerWhen struct { 163 timer *timer 164 when int64 165 } 166 167 // less reports whether tw is less than other. 168 func (tw timerWhen) less(other timerWhen) bool { 169 switch { 170 case tw.when < other.when: 171 return true 172 case tw.when > other.when: 173 return false 174 default: 175 // When timers wake at the same time, use a per-timer random value to order them. 176 // We only set the random value for timers using fake time, since there's 177 // no practical way to schedule real-time timers for the same instant. 178 return tw.timer.rand < other.timer.rand 179 } 180 } 181 182 func (ts *timers) lock() { 183 lock(&ts.mu) 184 } 185 186 func (ts *timers) unlock() { 187 // Update atomic copy of len(ts.heap). 188 // We only update at unlock so that the len is always 189 // the most recent unlocked length, not an ephemeral length. 190 // This matters if we lock ts, delete the only timer from the heap, 191 // add it back, and unlock. We want ts.len.Load to return 1 the 192 // entire time, never 0. This is important for pidleput deciding 193 // whether ts is empty. 194 ts.len.Store(uint32(len(ts.heap))) 195 196 unlock(&ts.mu) 197 } 198 199 // Timer state field. 200 const ( 201 // timerHeaped is set when the timer is stored in some P's heap. 202 timerHeaped uint8 = 1 << iota 203 204 // timerModified is set when t.when has been modified 205 // but the heap's heap[i].when entry still needs to be updated. 206 // That change waits until the heap in which 207 // the timer appears can be locked and rearranged. 208 // timerModified is only set when timerHeaped is also set. 209 timerModified 210 211 // timerZombie is set when the timer has been stopped 212 // but is still present in some P's heap. 213 // Only set when timerHeaped is also set. 214 // It is possible for timerModified and timerZombie to both 215 // be set, meaning that the timer was modified and then stopped. 216 // A timer sending to a channel may be placed in timerZombie 217 // to take it out of the heap even though the timer is not stopped, 218 // as long as nothing is reading from the channel. 219 timerZombie 220 ) 221 222 // timerDebug enables printing a textual debug trace of all timer operations to stderr. 223 const timerDebug = false 224 225 func (t *timer) trace(op string) { 226 if timerDebug { 227 t.trace1(op) 228 } 229 } 230 231 func (t *timer) trace1(op string) { 232 if !timerDebug { 233 return 234 } 235 bits := [4]string{"h", "m", "z", "c"} 236 for i := range 3 { 237 if t.state&(1<<i) == 0 { 238 bits[i] = "-" 239 } 240 } 241 if !t.isChan { 242 bits[3] = "-" 243 } 244 print("T ", t, " ", bits[0], bits[1], bits[2], bits[3], " b=", t.blocked, " ", op, "\n") 245 } 246 247 func (ts *timers) trace(op string) { 248 if timerDebug { 249 println("TS", ts, op) 250 } 251 } 252 253 // lock locks the timer, allowing reading or writing any of the timer fields. 254 func (t *timer) lock() { 255 lock(&t.mu) 256 t.trace("lock") 257 } 258 259 // unlock updates t.astate and unlocks the timer. 260 func (t *timer) unlock() { 261 t.trace("unlock") 262 // Let heap fast paths know whether heap[i].when is accurate. 263 // Also let maybeRunChan know whether channel is in heap. 264 t.astate.Store(t.state) 265 unlock(&t.mu) 266 } 267 268 // hchan returns the channel in t.arg. 269 // t must be a timer with a channel. 270 func (t *timer) hchan() *hchan { 271 if !t.isChan { 272 badTimer() 273 } 274 // Note: t.arg is a chan time.Time, 275 // and runtime cannot refer to that type, 276 // so we cannot use a type assertion. 277 return (*hchan)(efaceOf(&t.arg).data) 278 } 279 280 // updateHeap updates t as directed by t.state, updating t.state 281 // and returning a bool indicating whether the state (and ts.heap[0].when) changed. 282 // The caller must hold t's lock, or the world can be stopped instead. 283 // The timer set t.ts must be non-nil and locked, t must be t.ts.heap[0], and updateHeap 284 // takes care of moving t within the timers heap to preserve the heap invariants. 285 // If ts == nil, then t must not be in a heap (or is in a heap that is 286 // temporarily not maintaining its invariant, such as during timers.adjust). 287 func (t *timer) updateHeap() (updated bool) { 288 assertWorldStoppedOrLockHeld(&t.mu) 289 t.trace("updateHeap") 290 ts := t.ts 291 if ts == nil || t != ts.heap[0].timer { 292 badTimer() 293 } 294 assertLockHeld(&ts.mu) 295 if t.state&timerZombie != 0 { 296 // Take timer out of heap. 297 t.state &^= timerHeaped | timerZombie | timerModified 298 ts.zombies.Add(-1) 299 ts.deleteMin() 300 return true 301 } 302 303 if t.state&timerModified != 0 { 304 // Update ts.heap[0].when and move within heap. 305 t.state &^= timerModified 306 ts.heap[0].when = t.when 307 ts.siftDown(0) 308 ts.updateMinWhenHeap() 309 return true 310 } 311 312 return false 313 } 314 315 // maxWhen is the maximum value for timer's when field. 316 const maxWhen = 1<<63 - 1 317 318 // verifyTimers can be set to true to add debugging checks that the 319 // timer heaps are valid. 320 const verifyTimers = false 321 322 // Package time APIs. 323 // Godoc uses the comments in package time, not these. 324 325 // time.now is implemented in assembly. 326 327 // timeSleep puts the current goroutine to sleep for at least ns nanoseconds. 328 // 329 //go:linkname timeSleep time.Sleep 330 func timeSleep(ns int64) { 331 if ns <= 0 { 332 return 333 } 334 335 gp := getg() 336 t := gp.timer 337 if t == nil { 338 t = new(timer) 339 t.init(goroutineReady, gp) 340 if gp.bubble != nil { 341 t.isFake = true 342 } 343 gp.timer = t 344 } 345 var now int64 346 if bubble := gp.bubble; bubble != nil { 347 now = bubble.now 348 } else { 349 now = nanotime() 350 } 351 when := now + ns 352 if when < 0 { // check for overflow. 353 when = maxWhen 354 } 355 gp.sleepWhen = when 356 if t.isFake { 357 // Call timer.reset in this goroutine, since it's the one in a bubble. 358 // We don't need to worry about the timer function running before the goroutine 359 // is parked, because time won't advance until we park. 360 resetForSleep(gp, nil) 361 gopark(nil, nil, waitReasonSleep, traceBlockSleep, 1) 362 } else { 363 gopark(resetForSleep, nil, waitReasonSleep, traceBlockSleep, 1) 364 } 365 } 366 367 // resetForSleep is called after the goroutine is parked for timeSleep. 368 // We can't call timer.reset in timeSleep itself because if this is a short 369 // sleep and there are many goroutines then the P can wind up running the 370 // timer function, goroutineReady, before the goroutine has been parked. 371 func resetForSleep(gp *g, _ unsafe.Pointer) bool { 372 gp.timer.reset(gp.sleepWhen, 0) 373 return true 374 } 375 376 // A timeTimer is a runtime-allocated time.Timer or time.Ticker 377 // with the additional runtime state following it. 378 // The runtime state is inaccessible to package time. 379 type timeTimer struct { 380 c unsafe.Pointer // <-chan time.Time 381 init bool 382 timer 383 } 384 385 // newTimer allocates and returns a new time.Timer or time.Ticker (same layout) 386 // with the given parameters. 387 // 388 //go:linkname newTimer time.newTimer 389 func newTimer(when, period int64, f func(arg any, seq uintptr, delay int64), arg any, c *hchan) *timeTimer { 390 t := new(timeTimer) 391 t.timer.init(nil, nil) 392 t.trace("new") 393 if raceenabled { 394 racerelease(unsafe.Pointer(&t.timer)) 395 } 396 if c != nil { 397 lockInit(&t.sendLock, lockRankTimerSend) 398 t.isChan = true 399 c.timer = &t.timer 400 if c.dataqsiz == 0 { 401 throw("invalid timer channel: no capacity") 402 } 403 } 404 if bubble := getg().bubble; bubble != nil { 405 t.isFake = true 406 } 407 t.modify(when, period, f, arg, 0) 408 t.init = true 409 return t 410 } 411 412 // stopTimer stops a timer. 413 // It reports whether t was stopped before being run. 414 // 415 //go:linkname stopTimer time.stopTimer 416 func stopTimer(t *timeTimer) bool { 417 if t.isFake && getg().bubble == nil { 418 fatal("stop of synctest timer from outside bubble") 419 } 420 return t.stop() 421 } 422 423 // resetTimer resets an inactive timer, adding it to the timer heap. 424 // 425 // Reports whether the timer was modified before it was run. 426 // 427 //go:linkname resetTimer time.resetTimer 428 func resetTimer(t *timeTimer, when, period int64) bool { 429 if raceenabled { 430 racerelease(unsafe.Pointer(&t.timer)) 431 } 432 if t.isFake && getg().bubble == nil { 433 fatal("reset of synctest timer from outside bubble") 434 } 435 return t.reset(when, period) 436 } 437 438 // Go runtime. 439 440 // Ready the goroutine arg. 441 func goroutineReady(arg any, _ uintptr, _ int64) { 442 goready(arg.(*g), 0) 443 } 444 445 // addHeap adds t to the timers heap. 446 // The caller must hold ts.lock or the world must be stopped. 447 // The caller must also have checked that t belongs in the heap. 448 // Callers that are not sure can call t.maybeAdd instead, 449 // but note that maybeAdd has different locking requirements. 450 func (ts *timers) addHeap(t *timer) { 451 assertWorldStoppedOrLockHeld(&ts.mu) 452 // Timers rely on the network poller, so make sure the poller 453 // has started. 454 if netpollInited.Load() == 0 { 455 netpollGenericInit() 456 } 457 458 if t.ts != nil { 459 throw("ts set in timer") 460 } 461 t.ts = ts 462 ts.heap = append(ts.heap, timerWhen{t, t.when}) 463 ts.siftUp(len(ts.heap) - 1) 464 if t == ts.heap[0].timer { 465 ts.updateMinWhenHeap() 466 } 467 } 468 469 // maybeRunAsync checks whether t needs to be triggered and runs it if so. 470 // The caller is responsible for locking the timer and for checking that we 471 // are running timers in async mode. If the timer needs to be run, 472 // maybeRunAsync will unlock and re-lock it. 473 // The timer is always locked on return. 474 func (t *timer) maybeRunAsync() { 475 assertLockHeld(&t.mu) 476 if t.state&timerHeaped == 0 && t.isChan && t.when > 0 { 477 // If timer should have triggered already (but nothing looked at it yet), 478 // trigger now, so that a receive after the stop sees the "old" value 479 // that should be there. 480 // (It is possible to have t.blocked > 0 if there is a racing receive 481 // in blockTimerChan, but timerHeaped not being set means 482 // it hasn't run t.maybeAdd yet; in that case, running the 483 // timer ourselves now is fine.) 484 if now := nanotime(); t.when <= now { 485 systemstack(func() { 486 t.unlockAndRun(now, nil) // resets t.when 487 }) 488 t.lock() 489 } 490 } 491 } 492 493 // stop stops the timer t. It may be on some other P, so we can't 494 // actually remove it from the timers heap. We can only mark it as stopped. 495 // It will be removed in due course by the P whose heap it is on. 496 // Reports whether the timer was stopped before it was run. 497 func (t *timer) stop() bool { 498 async := debug.asynctimerchan.Load() != 0 499 if !async && t.isChan { 500 lock(&t.sendLock) 501 } 502 503 t.lock() 504 t.trace("stop") 505 if async { 506 t.maybeRunAsync() 507 } 508 if t.state&timerHeaped != 0 { 509 t.state |= timerModified 510 if t.state&timerZombie == 0 { 511 t.state |= timerZombie 512 t.ts.zombies.Add(1) 513 } 514 } 515 pending := t.when > 0 516 t.when = 0 517 518 if !async && t.isChan { 519 // Stop any future sends with stale values. 520 // See timer.unlockAndRun. 521 t.seq++ 522 523 // If there is currently a send in progress, 524 // incrementing seq is going to prevent that 525 // send from actually happening. That means 526 // that we should return true: the timer was 527 // stopped, even though t.when may be zero. 528 if t.period == 0 && t.isSending.Load() > 0 { 529 pending = true 530 } 531 } 532 t.unlock() 533 if !async && t.isChan { 534 unlock(&t.sendLock) 535 if timerchandrain(t.hchan()) { 536 pending = true 537 } 538 } 539 540 return pending 541 } 542 543 // deleteMin removes timer 0 from ts. 544 // ts must be locked. 545 func (ts *timers) deleteMin() { 546 assertLockHeld(&ts.mu) 547 t := ts.heap[0].timer 548 if t.ts != ts { 549 throw("wrong timers") 550 } 551 t.ts = nil 552 last := len(ts.heap) - 1 553 if last > 0 { 554 ts.heap[0] = ts.heap[last] 555 } 556 ts.heap[last] = timerWhen{} 557 ts.heap = ts.heap[:last] 558 if last > 0 { 559 ts.siftDown(0) 560 } 561 ts.updateMinWhenHeap() 562 if last == 0 { 563 // If there are no timers, then clearly there are no timerModified timers. 564 ts.minWhenModified.Store(0) 565 } 566 } 567 568 // modify modifies an existing timer. 569 // This is called by the netpoll code or time.Ticker.Reset or time.Timer.Reset. 570 // Reports whether the timer was modified before it was run. 571 // If f == nil, then t.f, t.arg, and t.seq are not modified. 572 func (t *timer) modify(when, period int64, f func(arg any, seq uintptr, delay int64), arg any, seq uintptr) bool { 573 if when <= 0 { 574 throw("timer when must be positive") 575 } 576 if period < 0 { 577 throw("timer period must be non-negative") 578 } 579 async := debug.asynctimerchan.Load() != 0 580 581 if !async && t.isChan { 582 lock(&t.sendLock) 583 } 584 585 t.lock() 586 if async { 587 t.maybeRunAsync() 588 } 589 t.trace("modify") 590 oldPeriod := t.period 591 t.period = period 592 if f != nil { 593 t.f = f 594 t.arg = arg 595 t.seq = seq 596 } 597 598 wake := false 599 pending := t.when > 0 600 t.when = when 601 if t.state&timerHeaped != 0 { 602 t.state |= timerModified 603 if t.state&timerZombie != 0 { 604 // In the heap but marked for removal (by a Stop). 605 // Unmark it, since it has been Reset and will be running again. 606 t.ts.zombies.Add(-1) 607 t.state &^= timerZombie 608 } 609 // The corresponding heap[i].when is updated later. 610 // See comment in type timer above and in timers.adjust below. 611 if min := t.ts.minWhenModified.Load(); min == 0 || when < min { 612 wake = true 613 // Force timerModified bit out to t.astate before updating t.minWhenModified, 614 // to synchronize with t.ts.adjust. See comment in adjust. 615 t.astate.Store(t.state) 616 t.ts.updateMinWhenModified(when) 617 } 618 } 619 620 add := t.needsAdd() 621 622 if add && t.isFake { 623 // If this is a bubbled timer scheduled to fire immediately, 624 // run it now rather than waiting for the bubble's timer scheduler. 625 // This avoids deferring timer execution until after the bubble 626 // becomes durably blocked. 627 // 628 // Don't do this for non-bubbled timers: It isn't necessary, 629 // and there may be cases where the runtime executes timers with 630 // the expectation the timer func will not run in the current goroutine. 631 // Bubbled timers are always created by the time package, and are 632 // safe to run in the current goroutine. 633 bubble := getg().bubble 634 if bubble == nil { 635 throw("fake timer executing with no bubble") 636 } 637 if t.state&timerHeaped == 0 && when <= bubble.now { 638 systemstack(func() { 639 if !async && t.isChan { 640 unlock(&t.sendLock) 641 } 642 t.unlockAndRun(bubble.now, bubble) 643 }) 644 return pending 645 } 646 } 647 648 if !async && t.isChan { 649 // Stop any future sends with stale values. 650 // See timer.unlockAndRun. 651 t.seq++ 652 653 // If there is currently a send in progress, 654 // incrementing seq is going to prevent that 655 // send from actually happening. That means 656 // that we should return true: the timer was 657 // stopped, even though t.when may be zero. 658 if oldPeriod == 0 && t.isSending.Load() > 0 { 659 pending = true 660 } 661 } 662 t.unlock() 663 if !async && t.isChan { 664 if timerchandrain(t.hchan()) { 665 pending = true 666 } 667 unlock(&t.sendLock) 668 } 669 670 if add { 671 t.maybeAdd() 672 } 673 if wake { 674 wakeNetPoller(when) 675 } 676 677 return pending 678 } 679 680 // needsAdd reports whether t needs to be added to a timers heap. 681 // t must be locked. 682 func (t *timer) needsAdd() bool { 683 assertLockHeld(&t.mu) 684 need := t.state&timerHeaped == 0 && t.when > 0 && (!t.isChan || t.blocked > 0) 685 if need { 686 t.trace("needsAdd+") 687 } else { 688 t.trace("needsAdd-") 689 } 690 return need 691 } 692 693 // maybeAdd adds t to the local timers heap if it needs to be in a heap. 694 // The caller must not hold t's lock nor any timers heap lock. 695 // The caller probably just unlocked t, but that lock must be dropped 696 // in order to acquire a ts.lock, to avoid lock inversions. 697 // (timers.adjust holds ts.lock while acquiring each t's lock, 698 // so we cannot hold any t's lock while acquiring ts.lock). 699 // 700 // Strictly speaking it *might* be okay to hold t.lock and 701 // acquire ts.lock at the same time, because we know that 702 // t is not in any ts.heap, so nothing holding a ts.lock would 703 // be acquiring the t.lock at the same time, meaning there 704 // isn't a possible deadlock. But it is easier and safer not to be 705 // too clever and respect the static ordering. 706 // (If we don't, we have to change the static lock checking of t and ts.) 707 // 708 // Concurrent calls to time.Timer.Reset or blockTimerChan 709 // may result in concurrent calls to t.maybeAdd, 710 // so we cannot assume that t is not in a heap on entry to t.maybeAdd. 711 func (t *timer) maybeAdd() { 712 // Note: Not holding any locks on entry to t.maybeAdd, 713 // so the current g can be rescheduled to a different M and P 714 // at any time, including between the ts := assignment and the 715 // call to ts.lock. If a reschedule happened then, we would be 716 // adding t to some other P's timers, perhaps even a P that the scheduler 717 // has marked as idle with no timers, in which case the timer could 718 // go unnoticed until long after t.when. 719 // Calling acquirem instead of using getg().m makes sure that 720 // we end up locking and inserting into the current P's timers. 721 mp := acquirem() 722 var ts *timers 723 if t.isFake { 724 bubble := getg().bubble 725 if bubble == nil { 726 throw("invalid timer: fake time but no syncgroup") 727 } 728 ts = &bubble.timers 729 } else { 730 ts = &mp.p.ptr().timers 731 } 732 ts.lock() 733 ts.cleanHead() 734 t.lock() 735 t.trace("maybeAdd") 736 when := int64(0) 737 wake := false 738 if t.needsAdd() { 739 if t.isFake { 740 // Re-randomize timer order. 741 // We could do this for all timers, but unbubbled timers are highly 742 // unlikely to have the same when. 743 t.rand = cheaprand() 744 } 745 t.state |= timerHeaped 746 when = t.when 747 wakeTime := ts.wakeTime() 748 wake = wakeTime == 0 || when < wakeTime 749 ts.addHeap(t) 750 } 751 t.unlock() 752 ts.unlock() 753 releasem(mp) 754 if wake { 755 wakeNetPoller(when) 756 } 757 } 758 759 // reset resets the time when a timer should fire. 760 // If used for an inactive timer, the timer will become active. 761 // Reports whether the timer was active and was stopped. 762 func (t *timer) reset(when, period int64) bool { 763 return t.modify(when, period, nil, nil, 0) 764 } 765 766 // cleanHead cleans up the head of the timer queue. This speeds up 767 // programs that create and delete timers; leaving them in the heap 768 // slows down heap operations. 769 // The caller must have locked ts. 770 func (ts *timers) cleanHead() { 771 ts.trace("cleanHead") 772 assertLockHeld(&ts.mu) 773 gp := getg() 774 for { 775 if len(ts.heap) == 0 { 776 return 777 } 778 779 // This loop can theoretically run for a while, and because 780 // it is holding timersLock it cannot be preempted. 781 // If someone is trying to preempt us, just return. 782 // We can clean the timers later. 783 if gp.preemptStop { 784 return 785 } 786 787 // Delete zombies from tail of heap. It requires no heap adjustments at all, 788 // and doing so increases the chances that when we swap out a zombie 789 // in heap[0] for the tail of the heap, we'll get a non-zombie timer, 790 // shortening this loop. 791 n := len(ts.heap) 792 if t := ts.heap[n-1].timer; t.astate.Load()&timerZombie != 0 { 793 t.lock() 794 if t.state&timerZombie != 0 { 795 t.state &^= timerHeaped | timerZombie | timerModified 796 t.ts = nil 797 ts.zombies.Add(-1) 798 ts.heap[n-1] = timerWhen{} 799 ts.heap = ts.heap[:n-1] 800 } 801 t.unlock() 802 continue 803 } 804 805 t := ts.heap[0].timer 806 if t.ts != ts { 807 throw("bad ts") 808 } 809 810 if t.astate.Load()&(timerModified|timerZombie) == 0 { 811 // Fast path: head of timers does not need adjustment. 812 return 813 } 814 815 t.lock() 816 updated := t.updateHeap() 817 t.unlock() 818 if !updated { 819 // Head of timers does not need adjustment. 820 return 821 } 822 } 823 } 824 825 // take moves any timers from src into ts 826 // and then clears the timer state from src, 827 // because src is being destroyed. 828 // The caller must not have locked either timers. 829 // For now this is only called when the world is stopped. 830 func (ts *timers) take(src *timers) { 831 ts.trace("take") 832 assertWorldStopped() 833 if len(src.heap) > 0 { 834 // The world is stopped, so we ignore the locking of ts and src here. 835 // That would introduce a sched < timers lock ordering, 836 // which we'd rather avoid in the static ranking. 837 for _, tw := range src.heap { 838 t := tw.timer 839 t.ts = nil 840 if t.state&timerZombie != 0 { 841 t.state &^= timerHeaped | timerZombie | timerModified 842 } else { 843 t.state &^= timerModified 844 ts.addHeap(t) 845 } 846 } 847 src.heap = nil 848 src.zombies.Store(0) 849 src.minWhenHeap.Store(0) 850 src.minWhenModified.Store(0) 851 src.len.Store(0) 852 ts.len.Store(uint32(len(ts.heap))) 853 } 854 } 855 856 // adjust looks through the timers in ts.heap for 857 // any timers that have been modified to run earlier, and puts them in 858 // the correct place in the heap. While looking for those timers, 859 // it also moves timers that have been modified to run later, 860 // and removes deleted timers. The caller must have locked ts. 861 func (ts *timers) adjust(now int64, force bool) { 862 ts.trace("adjust") 863 assertLockHeld(&ts.mu) 864 // If we haven't yet reached the time of the earliest modified 865 // timer, don't do anything. This speeds up programs that adjust 866 // a lot of timers back and forth if the timers rarely expire. 867 // We'll postpone looking through all the adjusted timers until 868 // one would actually expire. 869 if !force { 870 first := ts.minWhenModified.Load() 871 if first == 0 || first > now { 872 if verifyTimers { 873 ts.verify() 874 } 875 return 876 } 877 } 878 879 // minWhenModified is a lower bound on the earliest t.when 880 // among the timerModified timers. We want to make it more precise: 881 // we are going to scan the heap and clean out all the timerModified bits, 882 // at which point minWhenModified can be set to 0 (indicating none at all). 883 // 884 // Other P's can be calling ts.wakeTime concurrently, and we'd like to 885 // keep ts.wakeTime returning an accurate value throughout this entire process. 886 // 887 // Setting minWhenModified = 0 *before* the scan could make wakeTime 888 // return an incorrect value: if minWhenModified < minWhenHeap, then clearing 889 // it to 0 will make wakeTime return minWhenHeap (too late) until the scan finishes. 890 // To avoid that, we want to set minWhenModified to 0 *after* the scan. 891 // 892 // Setting minWhenModified = 0 *after* the scan could result in missing 893 // concurrent timer modifications in other goroutines; those will lock 894 // the specific timer, set the timerModified bit, and set t.when. 895 // To avoid that, we want to set minWhenModified to 0 *before* the scan. 896 // 897 // The way out of this dilemma is to preserve wakeTime a different way. 898 // wakeTime is min(minWhenHeap, minWhenModified), and minWhenHeap 899 // is protected by ts.lock, which we hold, so we can modify it however we like 900 // in service of keeping wakeTime accurate. 901 // 902 // So we can: 903 // 904 // 1. Set minWhenHeap = min(minWhenHeap, minWhenModified) 905 // 2. Set minWhenModified = 0 906 // (Other goroutines may modify timers and update minWhenModified now.) 907 // 3. Scan timers 908 // 4. Set minWhenHeap = heap[0].when 909 // 910 // That order preserves a correct value of wakeTime throughout the entire 911 // operation: 912 // Step 1 “locks in” an accurate wakeTime even with minWhenModified cleared. 913 // Step 2 makes sure concurrent t.when updates are not lost during the scan. 914 // Step 3 processes all modified timer values, justifying minWhenModified = 0. 915 // Step 4 corrects minWhenHeap to a precise value. 916 // 917 // The wakeTime method implementation reads minWhenModified *before* minWhenHeap, 918 // so that if the minWhenModified is observed to be 0, that means the minWhenHeap that 919 // follows will include the information that was zeroed out of it. 920 // 921 // Originally Step 3 locked every timer, which made sure any timer update that was 922 // already in progress during Steps 1+2 completed and was observed by Step 3. 923 // All that locking was too expensive, so now we do an atomic load of t.astate to 924 // decide whether we need to do a full lock. To make sure that we still observe any 925 // timer update already in progress during Steps 1+2, t.modify sets timerModified 926 // in t.astate *before* calling t.updateMinWhenModified. That ensures that the 927 // overwrite in Step 2 cannot lose an update: if it does overwrite an update, Step 3 928 // will see the timerModified and do a full lock. 929 ts.minWhenHeap.Store(ts.wakeTime()) 930 ts.minWhenModified.Store(0) 931 932 changed := false 933 for i := 0; i < len(ts.heap); i++ { 934 tw := &ts.heap[i] 935 t := tw.timer 936 if t.ts != ts { 937 throw("bad ts") 938 } 939 940 if t.astate.Load()&(timerModified|timerZombie) == 0 { 941 // Does not need adjustment. 942 continue 943 } 944 945 t.lock() 946 switch { 947 case t.state&timerHeaped == 0: 948 badTimer() 949 950 case t.state&timerZombie != 0: 951 ts.zombies.Add(-1) 952 t.state &^= timerHeaped | timerZombie | timerModified 953 n := len(ts.heap) 954 ts.heap[i] = ts.heap[n-1] 955 ts.heap[n-1] = timerWhen{} 956 ts.heap = ts.heap[:n-1] 957 t.ts = nil 958 i-- 959 changed = true 960 961 case t.state&timerModified != 0: 962 tw.when = t.when 963 t.state &^= timerModified 964 changed = true 965 } 966 t.unlock() 967 } 968 969 if changed { 970 ts.initHeap() 971 } 972 ts.updateMinWhenHeap() 973 974 if verifyTimers { 975 ts.verify() 976 } 977 } 978 979 // wakeTime looks at ts's timers and returns the time when we 980 // should wake up the netpoller. It returns 0 if there are no timers. 981 // This function is invoked when dropping a P, so it must run without 982 // any write barriers. 983 // 984 //go:nowritebarrierrec 985 func (ts *timers) wakeTime() int64 { 986 // Note that the order of these two loads matters: 987 // adjust updates minWhen to make it safe to clear minNextWhen. 988 // We read minWhen after reading minNextWhen so that 989 // if we see a cleared minNextWhen, we are guaranteed to see 990 // the updated minWhen. 991 nextWhen := ts.minWhenModified.Load() 992 when := ts.minWhenHeap.Load() 993 if when == 0 || (nextWhen != 0 && nextWhen < when) { 994 when = nextWhen 995 } 996 return when 997 } 998 999 // check runs any timers in ts that are ready. 1000 // If now is not 0 it is the current time. 1001 // It returns the passed time or the current time if now was passed as 0. 1002 // and the time when the next timer should run or 0 if there is no next timer, 1003 // and reports whether it ran any timers. 1004 // If the time when the next timer should run is not 0, 1005 // it is always larger than the returned time. 1006 // We pass now in and out to avoid extra calls of nanotime. 1007 // 1008 //go:yeswritebarrierrec 1009 func (ts *timers) check(now int64, bubble *synctestBubble) (rnow, pollUntil int64, ran bool) { 1010 ts.trace("check") 1011 // If it's not yet time for the first timer, or the first adjusted 1012 // timer, then there is nothing to do. 1013 next := ts.wakeTime() 1014 if next == 0 { 1015 // No timers to run or adjust. 1016 return now, 0, false 1017 } 1018 1019 if now == 0 { 1020 now = nanotime() 1021 } 1022 1023 // If this is the local P, and there are a lot of deleted timers, 1024 // clear them out. We only do this for the local P to reduce 1025 // lock contention on timersLock. 1026 zombies := ts.zombies.Load() 1027 if zombies < 0 { 1028 badTimer() 1029 } 1030 force := ts == &getg().m.p.ptr().timers && int(zombies) > int(ts.len.Load())/4 1031 1032 if now < next && !force { 1033 // Next timer is not ready to run, and we don't need to clear deleted timers. 1034 return now, next, false 1035 } 1036 1037 ts.lock() 1038 if len(ts.heap) > 0 { 1039 ts.adjust(now, false) 1040 for len(ts.heap) > 0 { 1041 // Note that runtimer may temporarily unlock ts. 1042 if tw := ts.run(now, bubble); tw != 0 { 1043 if tw > 0 { 1044 pollUntil = tw 1045 } 1046 break 1047 } 1048 ran = true 1049 } 1050 1051 // Note: Delaying the forced adjustment until after the ts.run 1052 // (as opposed to calling ts.adjust(now, force) above) 1053 // is significantly faster under contention, such as in 1054 // package time's BenchmarkTimerAdjust10000, 1055 // though we do not fully understand why. 1056 force = ts == &getg().m.p.ptr().timers && int(ts.zombies.Load()) > int(ts.len.Load())/4 1057 if force { 1058 ts.adjust(now, true) 1059 } 1060 } 1061 ts.unlock() 1062 1063 return now, pollUntil, ran 1064 } 1065 1066 // run examines the first timer in ts. If it is ready based on now, 1067 // it runs the timer and removes or updates it. 1068 // Returns 0 if it ran a timer, -1 if there are no more timers, or the time 1069 // when the first timer should run. 1070 // The caller must have locked ts. 1071 // If a timer is run, this will temporarily unlock ts. 1072 // 1073 //go:systemstack 1074 func (ts *timers) run(now int64, bubble *synctestBubble) int64 { 1075 ts.trace("run") 1076 assertLockHeld(&ts.mu) 1077 Redo: 1078 if len(ts.heap) == 0 { 1079 return -1 1080 } 1081 tw := ts.heap[0] 1082 t := tw.timer 1083 if t.ts != ts { 1084 throw("bad ts") 1085 } 1086 1087 if t.astate.Load()&(timerModified|timerZombie) == 0 && tw.when > now { 1088 // Fast path: not ready to run. 1089 return tw.when 1090 } 1091 1092 t.lock() 1093 if t.updateHeap() { 1094 t.unlock() 1095 goto Redo 1096 } 1097 1098 if t.state&timerHeaped == 0 || t.state&timerModified != 0 { 1099 badTimer() 1100 } 1101 1102 if t.when > now { 1103 // Not ready to run. 1104 t.unlock() 1105 return t.when 1106 } 1107 1108 t.unlockAndRun(now, bubble) 1109 assertLockHeld(&ts.mu) // t is unlocked now, but not ts 1110 return 0 1111 } 1112 1113 // unlockAndRun unlocks and runs the timer t (which must be locked). 1114 // If t is in a timer set (t.ts != nil), the caller must also have locked the timer set, 1115 // and this call will temporarily unlock the timer set while running the timer function. 1116 // unlockAndRun returns with t unlocked and t.ts (re-)locked. 1117 // 1118 //go:systemstack 1119 func (t *timer) unlockAndRun(now int64, bubble *synctestBubble) { 1120 t.trace("unlockAndRun") 1121 assertLockHeld(&t.mu) 1122 if t.ts != nil { 1123 assertLockHeld(&t.ts.mu) 1124 } 1125 if raceenabled { 1126 // Note that we are running on a system stack, 1127 // so there is no chance of getg().m being reassigned 1128 // out from under us while this function executes. 1129 tsLocal := &getg().m.p.ptr().timers 1130 if tsLocal.raceCtx == 0 { 1131 tsLocal.raceCtx = racegostart(abi.FuncPCABIInternal((*timers).run) + sys.PCQuantum) 1132 } 1133 raceacquirectx(tsLocal.raceCtx, unsafe.Pointer(t)) 1134 } 1135 1136 if t.state&(timerModified|timerZombie) != 0 { 1137 badTimer() 1138 } 1139 1140 f := t.f 1141 arg := t.arg 1142 seq := t.seq 1143 var next int64 1144 delay := now - t.when 1145 if t.period > 0 { 1146 // Leave in heap but adjust next time to fire. 1147 next = t.when + t.period*(1+delay/t.period) 1148 if next < 0 { // check for overflow. 1149 next = maxWhen 1150 } 1151 } else { 1152 next = 0 1153 } 1154 ts := t.ts 1155 t.when = next 1156 if t.state&timerHeaped != 0 { 1157 t.state |= timerModified 1158 if next == 0 { 1159 t.state |= timerZombie 1160 t.ts.zombies.Add(1) 1161 } 1162 t.updateHeap() 1163 } 1164 1165 async := debug.asynctimerchan.Load() != 0 1166 if !async && t.isChan && t.period == 0 { 1167 // Tell Stop/Reset that we are sending a value. 1168 if t.isSending.Add(1) < 0 { 1169 throw("too many concurrent timer firings") 1170 } 1171 } 1172 1173 t.unlock() 1174 1175 if raceenabled { 1176 // Temporarily use the current P's racectx for g0. 1177 gp := getg() 1178 if gp.racectx != 0 { 1179 throw("unexpected racectx") 1180 } 1181 gp.racectx = gp.m.p.ptr().timers.raceCtx 1182 } 1183 1184 if ts != nil { 1185 ts.unlock() 1186 } 1187 1188 if bubble != nil { 1189 // Temporarily use the timer's synctest group for the G running this timer. 1190 gp := getg() 1191 if gp.bubble != nil { 1192 throw("unexpected syncgroup set") 1193 } 1194 gp.bubble = bubble 1195 bubble.changegstatus(gp, _Gdead, _Grunning) 1196 } 1197 1198 if !async && t.isChan { 1199 // For a timer channel, we want to make sure that no stale sends 1200 // happen after a t.stop or t.modify, but we cannot hold t.mu 1201 // during the actual send (which f does) due to lock ordering. 1202 // It can happen that we are holding t's lock above, we decide 1203 // it's time to send a time value (by calling f), grab the parameters, 1204 // unlock above, and then a t.stop or t.modify changes the timer 1205 // and returns. At that point, the send needs not to happen after all. 1206 // The way we arrange for it not to happen is that t.stop and t.modify 1207 // both increment t.seq while holding both t.mu and t.sendLock. 1208 // We copied the seq value above while holding t.mu. 1209 // Now we can acquire t.sendLock (which will be held across the send) 1210 // and double-check that t.seq is still the seq value we saw above. 1211 // If not, the timer has been updated and we should skip the send. 1212 // We skip the send by reassigning f to a no-op function. 1213 // 1214 // The isSending field tells t.stop or t.modify that we have 1215 // started to send the value. That lets them correctly return 1216 // true meaning that no value was sent. 1217 lock(&t.sendLock) 1218 1219 if t.period == 0 { 1220 // We are committed to possibly sending a value 1221 // based on seq, so no need to keep telling 1222 // stop/modify that we are sending. 1223 if t.isSending.Add(-1) < 0 { 1224 throw("mismatched isSending updates") 1225 } 1226 } 1227 1228 if t.seq != seq { 1229 f = func(any, uintptr, int64) {} 1230 } 1231 } 1232 1233 f(arg, seq, delay) 1234 1235 if !async && t.isChan { 1236 unlock(&t.sendLock) 1237 } 1238 1239 if bubble != nil { 1240 gp := getg() 1241 bubble.changegstatus(gp, _Grunning, _Gdead) 1242 if raceenabled { 1243 // Establish a happens-before between this timer event and 1244 // the next synctest.Wait call. 1245 racereleasemergeg(gp, bubble.raceaddr()) 1246 } 1247 gp.bubble = nil 1248 } 1249 1250 if ts != nil { 1251 ts.lock() 1252 } 1253 1254 if raceenabled { 1255 gp := getg() 1256 gp.racectx = 0 1257 } 1258 } 1259 1260 // verifyTimerHeap verifies that the timers is in a valid state. 1261 // This is only for debugging, and is only called if verifyTimers is true. 1262 // The caller must have locked ts. 1263 func (ts *timers) verify() { 1264 assertLockHeld(&ts.mu) 1265 for i, tw := range ts.heap { 1266 if i == 0 { 1267 // First timer has no parent. 1268 continue 1269 } 1270 1271 // The heap is timerHeapN-ary. See siftupTimer and siftdownTimer. 1272 p := int(uint(i-1) / timerHeapN) 1273 if tw.less(ts.heap[p]) { 1274 print("bad timer heap at ", i, ": ", p, ": ", ts.heap[p].when, ", ", i, ": ", tw.when, "\n") 1275 throw("bad timer heap") 1276 } 1277 } 1278 if n := int(ts.len.Load()); len(ts.heap) != n { 1279 println("timer heap len", len(ts.heap), "!= atomic len", n) 1280 throw("bad timer heap len") 1281 } 1282 } 1283 1284 // updateMinWhenHeap sets ts.minWhenHeap to ts.heap[0].when. 1285 // The caller must have locked ts or the world must be stopped. 1286 func (ts *timers) updateMinWhenHeap() { 1287 assertWorldStoppedOrLockHeld(&ts.mu) 1288 if len(ts.heap) == 0 { 1289 ts.minWhenHeap.Store(0) 1290 } else { 1291 ts.minWhenHeap.Store(ts.heap[0].when) 1292 } 1293 } 1294 1295 // updateMinWhenModified updates ts.minWhenModified to be <= when. 1296 // ts need not be (and usually is not) locked. 1297 func (ts *timers) updateMinWhenModified(when int64) { 1298 for { 1299 old := ts.minWhenModified.Load() 1300 if old != 0 && old < when { 1301 return 1302 } 1303 if ts.minWhenModified.CompareAndSwap(old, when) { 1304 return 1305 } 1306 } 1307 } 1308 1309 // timeSleepUntil returns the time when the next timer should fire. Returns 1310 // maxWhen if there are no timers. 1311 // This is only called by sysmon and checkdead. 1312 func timeSleepUntil() int64 { 1313 next := int64(maxWhen) 1314 1315 // Prevent allp slice changes. This is like retake. 1316 lock(&allpLock) 1317 for _, pp := range allp { 1318 if pp == nil { 1319 // This can happen if procresize has grown 1320 // allp but not yet created new Ps. 1321 continue 1322 } 1323 1324 if w := pp.timers.wakeTime(); w != 0 { 1325 next = min(next, w) 1326 } 1327 } 1328 unlock(&allpLock) 1329 1330 return next 1331 } 1332 1333 const timerHeapN = 4 1334 1335 // Heap maintenance algorithms. 1336 // These algorithms check for slice index errors manually. 1337 // Slice index error can happen if the program is using racy 1338 // access to timers. We don't want to panic here, because 1339 // it will cause the program to crash with a mysterious 1340 // "panic holding locks" message. Instead, we panic while not 1341 // holding a lock. 1342 1343 // siftUp puts the timer at position i in the right place 1344 // in the heap by moving it up toward the top of the heap. 1345 func (ts *timers) siftUp(i int) { 1346 heap := ts.heap 1347 if i >= len(heap) { 1348 badTimer() 1349 } 1350 tw := heap[i] 1351 if tw.when <= 0 { 1352 badTimer() 1353 } 1354 for i > 0 { 1355 p := int(uint(i-1) / timerHeapN) // parent 1356 if !tw.less(heap[p]) { 1357 break 1358 } 1359 heap[i] = heap[p] 1360 i = p 1361 } 1362 if heap[i].timer != tw.timer { 1363 heap[i] = tw 1364 } 1365 } 1366 1367 // siftDown puts the timer at position i in the right place 1368 // in the heap by moving it down toward the bottom of the heap. 1369 func (ts *timers) siftDown(i int) { 1370 heap := ts.heap 1371 n := len(heap) 1372 if i >= n { 1373 badTimer() 1374 } 1375 if i*timerHeapN+1 >= n { 1376 return 1377 } 1378 tw := heap[i] 1379 if tw.when <= 0 { 1380 badTimer() 1381 } 1382 for { 1383 leftChild := i*timerHeapN + 1 1384 if leftChild >= n { 1385 break 1386 } 1387 w := tw 1388 c := -1 1389 for j, tw := range heap[leftChild:min(leftChild+timerHeapN, n)] { 1390 if tw.less(w) { 1391 w = tw 1392 c = leftChild + j 1393 } 1394 } 1395 if c < 0 { 1396 break 1397 } 1398 heap[i] = heap[c] 1399 i = c 1400 } 1401 if heap[i].timer != tw.timer { 1402 heap[i] = tw 1403 } 1404 } 1405 1406 // initHeap reestablishes the heap order in the slice ts.heap. 1407 // It takes O(n) time for n=len(ts.heap), not the O(n log n) of n repeated add operations. 1408 func (ts *timers) initHeap() { 1409 // Last possible element that needs sifting down is parent of last element; 1410 // last element is len(t)-1; parent of last element is (len(t)-1-1)/timerHeapN. 1411 if len(ts.heap) <= 1 { 1412 return 1413 } 1414 for i := int(uint(len(ts.heap)-1-1) / timerHeapN); i >= 0; i-- { 1415 ts.siftDown(i) 1416 } 1417 } 1418 1419 // badTimer is called if the timer data structures have been corrupted, 1420 // presumably due to racy use by the program. We panic here rather than 1421 // panicking due to invalid slice access while holding locks. 1422 // See issue #25686. 1423 func badTimer() { 1424 throw("timer data corruption") 1425 } 1426 1427 // Timer channels. 1428 1429 // maybeRunChan checks whether the timer needs to run 1430 // to send a value to its associated channel. If so, it does. 1431 // The timer must not be locked. 1432 func (t *timer) maybeRunChan(c *hchan) { 1433 if t.isFake && getg().bubble != c.bubble { 1434 // This should have been checked by the caller, but check just in case. 1435 fatal("synctest timer accessed from outside bubble") 1436 } 1437 if t.astate.Load()&timerHeaped != 0 { 1438 // If the timer is in the heap, the ordinary timer code 1439 // is in charge of sending when appropriate. 1440 return 1441 } 1442 1443 t.lock() 1444 now := nanotime() 1445 if t.isFake { 1446 now = getg().bubble.now 1447 } 1448 if t.state&timerHeaped != 0 || t.when == 0 || t.when > now { 1449 t.trace("maybeRunChan-") 1450 // Timer in the heap, or not running at all, or not triggered. 1451 t.unlock() 1452 return 1453 } 1454 t.trace("maybeRunChan+") 1455 systemstack(func() { 1456 t.unlockAndRun(now, c.bubble) 1457 }) 1458 } 1459 1460 // blockTimerChan is called when a channel op has decided to block on c. 1461 // The caller holds the channel lock for c and possibly other channels. 1462 // blockTimerChan makes sure that c is in a timer heap, 1463 // adding it if needed. 1464 func blockTimerChan(c *hchan) { 1465 t := c.timer 1466 if t.isFake && c.bubble != getg().bubble { 1467 // This should have been checked by the caller, but check just in case. 1468 fatal("synctest timer accessed from outside bubble") 1469 } 1470 1471 t.lock() 1472 t.trace("blockTimerChan") 1473 if !t.isChan { 1474 badTimer() 1475 } 1476 1477 t.blocked++ 1478 1479 // If this is the first enqueue after a recent dequeue, 1480 // the timer may still be in the heap but marked as a zombie. 1481 // Unmark it in this case, if the timer is still pending. 1482 if t.state&timerHeaped != 0 && t.state&timerZombie != 0 && t.when > 0 { 1483 t.state &^= timerZombie 1484 t.ts.zombies.Add(-1) 1485 } 1486 1487 // t.maybeAdd must be called with t unlocked, 1488 // because it needs to lock t.ts before t. 1489 // Then it will do nothing if t.needsAdd(state) is false. 1490 // Check that now before the unlock, 1491 // avoiding the extra lock-lock-unlock-unlock 1492 // inside maybeAdd when t does not need to be added. 1493 add := t.needsAdd() 1494 t.unlock() 1495 if add { 1496 t.maybeAdd() 1497 } 1498 } 1499 1500 // unblockTimerChan is called when a channel op that was blocked on c 1501 // is no longer blocked. Every call to blockTimerChan must be paired with 1502 // a call to unblockTimerChan. 1503 // The caller holds the channel lock for c and possibly other channels. 1504 // unblockTimerChan removes c from the timer heap when nothing is 1505 // blocked on it anymore. 1506 func unblockTimerChan(c *hchan) { 1507 t := c.timer 1508 t.lock() 1509 t.trace("unblockTimerChan") 1510 if !t.isChan || t.blocked == 0 { 1511 badTimer() 1512 } 1513 t.blocked-- 1514 if t.blocked == 0 && t.state&timerHeaped != 0 && t.state&timerZombie == 0 { 1515 // Last goroutine that was blocked on this timer. 1516 // Mark for removal from heap but do not clear t.when, 1517 // so that we know what time it is still meant to trigger. 1518 t.state |= timerZombie 1519 t.ts.zombies.Add(1) 1520 } 1521 t.unlock() 1522 } 1523