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 package runtime 6 7 import ( 8 "internal/abi" 9 "internal/chacha8rand" 10 "internal/goarch" 11 "runtime/internal/atomic" 12 "runtime/internal/sys" 13 "unsafe" 14 ) 15 16 // defined constants 17 const ( 18 // G status 19 // 20 // Beyond indicating the general state of a G, the G status 21 // acts like a lock on the goroutine's stack (and hence its 22 // ability to execute user code). 23 // 24 // If you add to this list, add to the list 25 // of "okay during garbage collection" status 26 // in mgcmark.go too. 27 // 28 // TODO(austin): The _Gscan bit could be much lighter-weight. 29 // For example, we could choose not to run _Gscanrunnable 30 // goroutines found in the run queue, rather than CAS-looping 31 // until they become _Grunnable. And transitions like 32 // _Gscanwaiting -> _Gscanrunnable are actually okay because 33 // they don't affect stack ownership. 34 35 // _Gidle means this goroutine was just allocated and has not 36 // yet been initialized. 37 _Gidle = iota // 0 38 39 // _Grunnable means this goroutine is on a run queue. It is 40 // not currently executing user code. The stack is not owned. 41 _Grunnable // 1 42 43 // _Grunning means this goroutine may execute user code. The 44 // stack is owned by this goroutine. It is not on a run queue. 45 // It is assigned an M and a P (g.m and g.m.p are valid). 46 _Grunning // 2 47 48 // _Gsyscall means this goroutine is executing a system call. 49 // It is not executing user code. The stack is owned by this 50 // goroutine. It is not on a run queue. It is assigned an M. 51 _Gsyscall // 3 52 53 // _Gwaiting means this goroutine is blocked in the runtime. 54 // It is not executing user code. It is not on a run queue, 55 // but should be recorded somewhere (e.g., a channel wait 56 // queue) so it can be ready()d when necessary. The stack is 57 // not owned *except* that a channel operation may read or 58 // write parts of the stack under the appropriate channel 59 // lock. Otherwise, it is not safe to access the stack after a 60 // goroutine enters _Gwaiting (e.g., it may get moved). 61 _Gwaiting // 4 62 63 // _Gmoribund_unused is currently unused, but hardcoded in gdb 64 // scripts. 65 _Gmoribund_unused // 5 66 67 // _Gdead means this goroutine is currently unused. It may be 68 // just exited, on a free list, or just being initialized. It 69 // is not executing user code. It may or may not have a stack 70 // allocated. The G and its stack (if any) are owned by the M 71 // that is exiting the G or that obtained the G from the free 72 // list. 73 _Gdead // 6 74 75 // _Genqueue_unused is currently unused. 76 _Genqueue_unused // 7 77 78 // _Gcopystack means this goroutine's stack is being moved. It 79 // is not executing user code and is not on a run queue. The 80 // stack is owned by the goroutine that put it in _Gcopystack. 81 _Gcopystack // 8 82 83 // _Gpreempted means this goroutine stopped itself for a 84 // suspendG preemption. It is like _Gwaiting, but nothing is 85 // yet responsible for ready()ing it. Some suspendG must CAS 86 // the status to _Gwaiting to take responsibility for 87 // ready()ing this G. 88 _Gpreempted // 9 89 90 // _Gscan combined with one of the above states other than 91 // _Grunning indicates that GC is scanning the stack. The 92 // goroutine is not executing user code and the stack is owned 93 // by the goroutine that set the _Gscan bit. 94 // 95 // _Gscanrunning is different: it is used to briefly block 96 // state transitions while GC signals the G to scan its own 97 // stack. This is otherwise like _Grunning. 98 // 99 // atomicstatus&~Gscan gives the state the goroutine will 100 // return to when the scan completes. 101 _Gscan = 0x1000 102 _Gscanrunnable = _Gscan + _Grunnable // 0x1001 103 _Gscanrunning = _Gscan + _Grunning // 0x1002 104 _Gscansyscall = _Gscan + _Gsyscall // 0x1003 105 _Gscanwaiting = _Gscan + _Gwaiting // 0x1004 106 _Gscanpreempted = _Gscan + _Gpreempted // 0x1009 107 ) 108 109 const ( 110 // P status 111 112 // _Pidle means a P is not being used to run user code or the 113 // scheduler. Typically, it's on the idle P list and available 114 // to the scheduler, but it may just be transitioning between 115 // other states. 116 // 117 // The P is owned by the idle list or by whatever is 118 // transitioning its state. Its run queue is empty. 119 _Pidle = iota 120 121 // _Prunning means a P is owned by an M and is being used to 122 // run user code or the scheduler. Only the M that owns this P 123 // is allowed to change the P's status from _Prunning. The M 124 // may transition the P to _Pidle (if it has no more work to 125 // do), _Psyscall (when entering a syscall), or _Pgcstop (to 126 // halt for the GC). The M may also hand ownership of the P 127 // off directly to another M (e.g., to schedule a locked G). 128 _Prunning 129 130 // _Psyscall means a P is not running user code. It has 131 // affinity to an M in a syscall but is not owned by it and 132 // may be stolen by another M. This is similar to _Pidle but 133 // uses lightweight transitions and maintains M affinity. 134 // 135 // Leaving _Psyscall must be done with a CAS, either to steal 136 // or retake the P. Note that there's an ABA hazard: even if 137 // an M successfully CASes its original P back to _Prunning 138 // after a syscall, it must understand the P may have been 139 // used by another M in the interim. 140 _Psyscall 141 142 // _Pgcstop means a P is halted for STW and owned by the M 143 // that stopped the world. The M that stopped the world 144 // continues to use its P, even in _Pgcstop. Transitioning 145 // from _Prunning to _Pgcstop causes an M to release its P and 146 // park. 147 // 148 // The P retains its run queue and startTheWorld will restart 149 // the scheduler on Ps with non-empty run queues. 150 _Pgcstop 151 152 // _Pdead means a P is no longer used (GOMAXPROCS shrank). We 153 // reuse Ps if GOMAXPROCS increases. A dead P is mostly 154 // stripped of its resources, though a few things remain 155 // (e.g., trace buffers). 156 _Pdead 157 ) 158 159 // Mutual exclusion locks. In the uncontended case, 160 // as fast as spin locks (just a few user-level instructions), 161 // but on the contention path they sleep in the kernel. 162 // A zeroed Mutex is unlocked (no need to initialize each lock). 163 // Initialization is helpful for static lock ranking, but not required. 164 type mutex struct { 165 // Empty struct if lock ranking is disabled, otherwise includes the lock rank 166 lockRankStruct 167 // Futex-based impl treats it as uint32 key, 168 // while sema-based impl as M* waitm. 169 // Used to be a union, but unions break precise GC. 170 key uintptr 171 } 172 173 // sleep and wakeup on one-time events. 174 // before any calls to notesleep or notewakeup, 175 // must call noteclear to initialize the Note. 176 // then, exactly one thread can call notesleep 177 // and exactly one thread can call notewakeup (once). 178 // once notewakeup has been called, the notesleep 179 // will return. future notesleep will return immediately. 180 // subsequent noteclear must be called only after 181 // previous notesleep has returned, e.g. it's disallowed 182 // to call noteclear straight after notewakeup. 183 // 184 // notetsleep is like notesleep but wakes up after 185 // a given number of nanoseconds even if the event 186 // has not yet happened. if a goroutine uses notetsleep to 187 // wake up early, it must wait to call noteclear until it 188 // can be sure that no other goroutine is calling 189 // notewakeup. 190 // 191 // notesleep/notetsleep are generally called on g0, 192 // notetsleepg is similar to notetsleep but is called on user g. 193 type note struct { 194 // Futex-based impl treats it as uint32 key, 195 // while sema-based impl as M* waitm. 196 // Used to be a union, but unions break precise GC. 197 key uintptr 198 } 199 200 type funcval struct { 201 fn uintptr 202 // variable-size, fn-specific data here 203 } 204 205 type iface struct { 206 tab *itab 207 data unsafe.Pointer 208 } 209 210 type eface struct { 211 _type *_type 212 data unsafe.Pointer 213 } 214 215 func efaceOf(ep *any) *eface { 216 return (*eface)(unsafe.Pointer(ep)) 217 } 218 219 // The guintptr, muintptr, and puintptr are all used to bypass write barriers. 220 // It is particularly important to avoid write barriers when the current P has 221 // been released, because the GC thinks the world is stopped, and an 222 // unexpected write barrier would not be synchronized with the GC, 223 // which can lead to a half-executed write barrier that has marked the object 224 // but not queued it. If the GC skips the object and completes before the 225 // queuing can occur, it will incorrectly free the object. 226 // 227 // We tried using special assignment functions invoked only when not 228 // holding a running P, but then some updates to a particular memory 229 // word went through write barriers and some did not. This breaks the 230 // write barrier shadow checking mode, and it is also scary: better to have 231 // a word that is completely ignored by the GC than to have one for which 232 // only a few updates are ignored. 233 // 234 // Gs and Ps are always reachable via true pointers in the 235 // allgs and allp lists or (during allocation before they reach those lists) 236 // from stack variables. 237 // 238 // Ms are always reachable via true pointers either from allm or 239 // freem. Unlike Gs and Ps we do free Ms, so it's important that 240 // nothing ever hold an muintptr across a safe point. 241 242 // A guintptr holds a goroutine pointer, but typed as a uintptr 243 // to bypass write barriers. It is used in the Gobuf goroutine state 244 // and in scheduling lists that are manipulated without a P. 245 // 246 // The Gobuf.g goroutine pointer is almost always updated by assembly code. 247 // In one of the few places it is updated by Go code - func save - it must be 248 // treated as a uintptr to avoid a write barrier being emitted at a bad time. 249 // Instead of figuring out how to emit the write barriers missing in the 250 // assembly manipulation, we change the type of the field to uintptr, 251 // so that it does not require write barriers at all. 252 // 253 // Goroutine structs are published in the allg list and never freed. 254 // That will keep the goroutine structs from being collected. 255 // There is never a time that Gobuf.g's contain the only references 256 // to a goroutine: the publishing of the goroutine in allg comes first. 257 // Goroutine pointers are also kept in non-GC-visible places like TLS, 258 // so I can't see them ever moving. If we did want to start moving data 259 // in the GC, we'd need to allocate the goroutine structs from an 260 // alternate arena. Using guintptr doesn't make that problem any worse. 261 // Note that pollDesc.rg, pollDesc.wg also store g in uintptr form, 262 // so they would need to be updated too if g's start moving. 263 type guintptr uintptr 264 265 //go:nosplit 266 func (gp guintptr) ptr() *g { return (*g)(unsafe.Pointer(gp)) } 267 268 //go:nosplit 269 func (gp *guintptr) set(g *g) { *gp = guintptr(unsafe.Pointer(g)) } 270 271 //go:nosplit 272 func (gp *guintptr) cas(old, new guintptr) bool { 273 return atomic.Casuintptr((*uintptr)(unsafe.Pointer(gp)), uintptr(old), uintptr(new)) 274 } 275 276 //go:nosplit 277 func (gp *g) guintptr() guintptr { 278 return guintptr(unsafe.Pointer(gp)) 279 } 280 281 // setGNoWB performs *gp = new without a write barrier. 282 // For times when it's impractical to use a guintptr. 283 // 284 //go:nosplit 285 //go:nowritebarrier 286 func setGNoWB(gp **g, new *g) { 287 (*guintptr)(unsafe.Pointer(gp)).set(new) 288 } 289 290 type puintptr uintptr 291 292 //go:nosplit 293 func (pp puintptr) ptr() *p { return (*p)(unsafe.Pointer(pp)) } 294 295 //go:nosplit 296 func (pp *puintptr) set(p *p) { *pp = puintptr(unsafe.Pointer(p)) } 297 298 // muintptr is a *m that is not tracked by the garbage collector. 299 // 300 // Because we do free Ms, there are some additional constrains on 301 // muintptrs: 302 // 303 // 1. Never hold an muintptr locally across a safe point. 304 // 305 // 2. Any muintptr in the heap must be owned by the M itself so it can 306 // ensure it is not in use when the last true *m is released. 307 type muintptr uintptr 308 309 //go:nosplit 310 func (mp muintptr) ptr() *m { return (*m)(unsafe.Pointer(mp)) } 311 312 //go:nosplit 313 func (mp *muintptr) set(m *m) { *mp = muintptr(unsafe.Pointer(m)) } 314 315 // setMNoWB performs *mp = new without a write barrier. 316 // For times when it's impractical to use an muintptr. 317 // 318 //go:nosplit 319 //go:nowritebarrier 320 func setMNoWB(mp **m, new *m) { 321 (*muintptr)(unsafe.Pointer(mp)).set(new) 322 } 323 324 type gobuf struct { 325 // The offsets of sp, pc, and g are known to (hard-coded in) libmach. 326 // 327 // ctxt is unusual with respect to GC: it may be a 328 // heap-allocated funcval, so GC needs to track it, but it 329 // needs to be set and cleared from assembly, where it's 330 // difficult to have write barriers. However, ctxt is really a 331 // saved, live register, and we only ever exchange it between 332 // the real register and the gobuf. Hence, we treat it as a 333 // root during stack scanning, which means assembly that saves 334 // and restores it doesn't need write barriers. It's still 335 // typed as a pointer so that any other writes from Go get 336 // write barriers. 337 sp uintptr 338 pc uintptr 339 g guintptr 340 ctxt unsafe.Pointer 341 ret uintptr 342 lr uintptr 343 bp uintptr // for framepointer-enabled architectures 344 } 345 346 // sudog (pseudo-g) represents a g in a wait list, such as for sending/receiving 347 // on a channel. 348 // 349 // sudog is necessary because the g ↔ synchronization object relation 350 // is many-to-many. A g can be on many wait lists, so there may be 351 // many sudogs for one g; and many gs may be waiting on the same 352 // synchronization object, so there may be many sudogs for one object. 353 // 354 // sudogs are allocated from a special pool. Use acquireSudog and 355 // releaseSudog to allocate and free them. 356 type sudog struct { 357 // The following fields are protected by the hchan.lock of the 358 // channel this sudog is blocking on. shrinkstack depends on 359 // this for sudogs involved in channel ops. 360 361 g *g 362 363 next *sudog 364 prev *sudog 365 elem unsafe.Pointer // data element (may point to stack) 366 367 // The following fields are never accessed concurrently. 368 // For channels, waitlink is only accessed by g. 369 // For semaphores, all fields (including the ones above) 370 // are only accessed when holding a semaRoot lock. 371 372 acquiretime int64 373 releasetime int64 374 ticket uint32 375 376 // isSelect indicates g is participating in a select, so 377 // g.selectDone must be CAS'd to win the wake-up race. 378 isSelect bool 379 380 // success indicates whether communication over channel c 381 // succeeded. It is true if the goroutine was awoken because a 382 // value was delivered over channel c, and false if awoken 383 // because c was closed. 384 success bool 385 386 // waiters is a count of semaRoot waiting list other than head of list, 387 // clamped to a uint16 to fit in unused space. 388 // Only meaningful at the head of the list. 389 // (If we wanted to be overly clever, we could store a high 16 bits 390 // in the second entry in the list.) 391 waiters uint16 392 393 parent *sudog // semaRoot binary tree 394 waitlink *sudog // g.waiting list or semaRoot 395 waittail *sudog // semaRoot 396 c *hchan // channel 397 } 398 399 type libcall struct { 400 fn uintptr 401 n uintptr // number of parameters 402 args uintptr // parameters 403 r1 uintptr // return values 404 r2 uintptr 405 err uintptr // error number 406 } 407 408 // Stack describes a Go execution stack. 409 // The bounds of the stack are exactly [lo, hi), 410 // with no implicit data structures on either side. 411 type stack struct { 412 lo uintptr 413 hi uintptr 414 } 415 416 // heldLockInfo gives info on a held lock and the rank of that lock 417 type heldLockInfo struct { 418 lockAddr uintptr 419 rank lockRank 420 } 421 422 type g struct { 423 // Stack parameters. 424 // stack describes the actual stack memory: [stack.lo, stack.hi). 425 // stackguard0 is the stack pointer compared in the Go stack growth prologue. 426 // It is stack.lo+StackGuard normally, but can be StackPreempt to trigger a preemption. 427 // stackguard1 is the stack pointer compared in the //go:systemstack stack growth prologue. 428 // It is stack.lo+StackGuard on g0 and gsignal stacks. 429 // It is ~0 on other goroutine stacks, to trigger a call to morestackc (and crash). 430 stack stack // offset known to runtime/cgo 431 stackguard0 uintptr // offset known to liblink 432 stackguard1 uintptr // offset known to liblink 433 434 _panic *_panic // innermost panic - offset known to liblink 435 _defer *_defer // innermost defer 436 m *m // current m; offset known to arm liblink 437 sched gobuf 438 syscallsp uintptr // if status==Gsyscall, syscallsp = sched.sp to use during gc 439 syscallpc uintptr // if status==Gsyscall, syscallpc = sched.pc to use during gc 440 stktopsp uintptr // expected sp at top of stack, to check in traceback 441 // param is a generic pointer parameter field used to pass 442 // values in particular contexts where other storage for the 443 // parameter would be difficult to find. It is currently used 444 // in four ways: 445 // 1. When a channel operation wakes up a blocked goroutine, it sets param to 446 // point to the sudog of the completed blocking operation. 447 // 2. By gcAssistAlloc1 to signal back to its caller that the goroutine completed 448 // the GC cycle. It is unsafe to do so in any other way, because the goroutine's 449 // stack may have moved in the meantime. 450 // 3. By debugCallWrap to pass parameters to a new goroutine because allocating a 451 // closure in the runtime is forbidden. 452 // 4. When a panic is recovered and control returns to the respective frame, 453 // param may point to a savedOpenDeferState. 454 param unsafe.Pointer 455 atomicstatus atomic.Uint32 456 stackLock uint32 // sigprof/scang lock; TODO: fold in to atomicstatus 457 goid uint64 458 schedlink guintptr 459 waitsince int64 // approx time when the g become blocked 460 waitreason waitReason // if status==Gwaiting 461 462 preempt bool // preemption signal, duplicates stackguard0 = stackpreempt 463 preemptStop bool // transition to _Gpreempted on preemption; otherwise, just deschedule 464 preemptShrink bool // shrink stack at synchronous safe point 465 466 // asyncSafePoint is set if g is stopped at an asynchronous 467 // safe point. This means there are frames on the stack 468 // without precise pointer information. 469 asyncSafePoint bool 470 471 paniconfault bool // panic (instead of crash) on unexpected fault address 472 gcscandone bool // g has scanned stack; protected by _Gscan bit in status 473 throwsplit bool // must not split stack 474 // activeStackChans indicates that there are unlocked channels 475 // pointing into this goroutine's stack. If true, stack 476 // copying needs to acquire channel locks to protect these 477 // areas of the stack. 478 activeStackChans bool 479 // parkingOnChan indicates that the goroutine is about to 480 // park on a chansend or chanrecv. Used to signal an unsafe point 481 // for stack shrinking. 482 parkingOnChan atomic.Bool 483 // inMarkAssist indicates whether the goroutine is in mark assist. 484 // Used by the execution tracer. 485 inMarkAssist bool 486 coroexit bool // argument to coroswitch_m 487 488 raceignore int8 // ignore race detection events 489 nocgocallback bool // whether disable callback from C 490 tracking bool // whether we're tracking this G for sched latency statistics 491 trackingSeq uint8 // used to decide whether to track this G 492 trackingStamp int64 // timestamp of when the G last started being tracked 493 runnableTime int64 // the amount of time spent runnable, cleared when running, only used when tracking 494 lockedm muintptr 495 sig uint32 496 writebuf []byte 497 sigcode0 uintptr 498 sigcode1 uintptr 499 sigpc uintptr 500 parentGoid uint64 // goid of goroutine that created this goroutine 501 gopc uintptr // pc of go statement that created this goroutine 502 ancestors *[]ancestorInfo // ancestor information goroutine(s) that created this goroutine (only used if debug.tracebackancestors) 503 startpc uintptr // pc of goroutine function 504 racectx uintptr 505 waiting *sudog // sudog structures this g is waiting on (that have a valid elem ptr); in lock order 506 cgoCtxt []uintptr // cgo traceback context 507 labels unsafe.Pointer // profiler labels 508 timer *timer // cached timer for time.Sleep 509 selectDone atomic.Uint32 // are we participating in a select and did someone win the race? 510 511 coroarg *coro // argument during coroutine transfers 512 513 // goroutineProfiled indicates the status of this goroutine's stack for the 514 // current in-progress goroutine profile 515 goroutineProfiled goroutineProfileStateHolder 516 517 // Per-G tracer state. 518 trace gTraceState 519 520 // Per-G GC state 521 522 // gcAssistBytes is this G's GC assist credit in terms of 523 // bytes allocated. If this is positive, then the G has credit 524 // to allocate gcAssistBytes bytes without assisting. If this 525 // is negative, then the G must correct this by performing 526 // scan work. We track this in bytes to make it fast to update 527 // and check for debt in the malloc hot path. The assist ratio 528 // determines how this corresponds to scan work debt. 529 gcAssistBytes int64 530 } 531 532 // gTrackingPeriod is the number of transitions out of _Grunning between 533 // latency tracking runs. 534 const gTrackingPeriod = 8 535 536 const ( 537 // tlsSlots is the number of pointer-sized slots reserved for TLS on some platforms, 538 // like Windows. 539 tlsSlots = 6 540 tlsSize = tlsSlots * goarch.PtrSize 541 ) 542 543 // Values for m.freeWait. 544 const ( 545 freeMStack = 0 // M done, free stack and reference. 546 freeMRef = 1 // M done, free reference. 547 freeMWait = 2 // M still in use. 548 ) 549 550 type m struct { 551 g0 *g // goroutine with scheduling stack 552 morebuf gobuf // gobuf arg to morestack 553 divmod uint32 // div/mod denominator for arm - known to liblink 554 _ uint32 // align next field to 8 bytes 555 556 // Fields not known to debuggers. 557 procid uint64 // for debuggers, but offset not hard-coded 558 gsignal *g // signal-handling g 559 goSigStack gsignalStack // Go-allocated signal handling stack 560 sigmask sigset // storage for saved signal mask 561 tls [tlsSlots]uintptr // thread-local storage (for x86 extern register) 562 mstartfn func() 563 curg *g // current running goroutine 564 caughtsig guintptr // goroutine running during fatal signal 565 p puintptr // attached p for executing go code (nil if not executing go code) 566 nextp puintptr 567 oldp puintptr // the p that was attached before executing a syscall 568 id int64 569 mallocing int32 570 throwing throwType 571 preemptoff string // if != "", keep curg running on this m 572 locks int32 573 dying int32 574 profilehz int32 575 spinning bool // m is out of work and is actively looking for work 576 blocked bool // m is blocked on a note 577 newSigstack bool // minit on C thread called sigaltstack 578 printlock int8 579 incgo bool // m is executing a cgo call 580 isextra bool // m is an extra m 581 isExtraInC bool // m is an extra m that is not executing Go code 582 isExtraInSig bool // m is an extra m in a signal handler 583 freeWait atomic.Uint32 // Whether it is safe to free g0 and delete m (one of freeMRef, freeMStack, freeMWait) 584 needextram bool 585 traceback uint8 586 ncgocall uint64 // number of cgo calls in total 587 ncgo int32 // number of cgo calls currently in progress 588 cgoCallersUse atomic.Uint32 // if non-zero, cgoCallers in use temporarily 589 cgoCallers *cgoCallers // cgo traceback if crashing in cgo call 590 park note 591 alllink *m // on allm 592 schedlink muintptr 593 lockedg guintptr 594 createstack [32]uintptr // stack that created this thread, it's used for StackRecord.Stack0, so it must align with it. 595 lockedExt uint32 // tracking for external LockOSThread 596 lockedInt uint32 // tracking for internal lockOSThread 597 nextwaitm muintptr // next m waiting for lock 598 599 mLockProfile mLockProfile // fields relating to runtime.lock contention 600 601 // wait* are used to carry arguments from gopark into park_m, because 602 // there's no stack to put them on. That is their sole purpose. 603 waitunlockf func(*g, unsafe.Pointer) bool 604 waitlock unsafe.Pointer 605 waitTraceBlockReason traceBlockReason 606 waitTraceSkip int 607 608 syscalltick uint32 609 freelink *m // on sched.freem 610 trace mTraceState 611 612 // these are here because they are too large to be on the stack 613 // of low-level NOSPLIT functions. 614 libcall libcall 615 libcallpc uintptr // for cpu profiler 616 libcallsp uintptr 617 libcallg guintptr 618 syscall libcall // stores syscall parameters on windows 619 620 vdsoSP uintptr // SP for traceback while in VDSO call (0 if not in call) 621 vdsoPC uintptr // PC for traceback while in VDSO call 622 623 // preemptGen counts the number of completed preemption 624 // signals. This is used to detect when a preemption is 625 // requested, but fails. 626 preemptGen atomic.Uint32 627 628 // Whether this is a pending preemption signal on this M. 629 signalPending atomic.Uint32 630 631 // pcvalue lookup cache 632 pcvalueCache pcvalueCache 633 634 dlogPerM 635 636 mOS 637 638 chacha8 chacha8rand.State 639 cheaprand uint64 640 641 // Up to 10 locks held by this m, maintained by the lock ranking code. 642 locksHeldLen int 643 locksHeld [10]heldLockInfo 644 } 645 646 type p struct { 647 id int32 648 status uint32 // one of pidle/prunning/... 649 link puintptr 650 schedtick uint32 // incremented on every scheduler call 651 syscalltick uint32 // incremented on every system call 652 sysmontick sysmontick // last tick observed by sysmon 653 m muintptr // back-link to associated m (nil if idle) 654 mcache *mcache 655 pcache pageCache 656 raceprocctx uintptr 657 658 deferpool []*_defer // pool of available defer structs (see panic.go) 659 deferpoolbuf [32]*_defer 660 661 // Cache of goroutine ids, amortizes accesses to runtime·sched.goidgen. 662 goidcache uint64 663 goidcacheend uint64 664 665 // Queue of runnable goroutines. Accessed without lock. 666 runqhead uint32 667 runqtail uint32 668 runq [256]guintptr 669 // runnext, if non-nil, is a runnable G that was ready'd by 670 // the current G and should be run next instead of what's in 671 // runq if there's time remaining in the running G's time 672 // slice. It will inherit the time left in the current time 673 // slice. If a set of goroutines is locked in a 674 // communicate-and-wait pattern, this schedules that set as a 675 // unit and eliminates the (potentially large) scheduling 676 // latency that otherwise arises from adding the ready'd 677 // goroutines to the end of the run queue. 678 // 679 // Note that while other P's may atomically CAS this to zero, 680 // only the owner P can CAS it to a valid G. 681 runnext guintptr 682 683 // Available G's (status == Gdead) 684 gFree struct { 685 gList 686 n int32 687 } 688 689 sudogcache []*sudog 690 sudogbuf [128]*sudog 691 692 // Cache of mspan objects from the heap. 693 mspancache struct { 694 // We need an explicit length here because this field is used 695 // in allocation codepaths where write barriers are not allowed, 696 // and eliminating the write barrier/keeping it eliminated from 697 // slice updates is tricky, more so than just managing the length 698 // ourselves. 699 len int 700 buf [128]*mspan 701 } 702 703 // Cache of a single pinner object to reduce allocations from repeated 704 // pinner creation. 705 pinnerCache *pinner 706 707 trace pTraceState 708 709 palloc persistentAlloc // per-P to avoid mutex 710 711 // The when field of the first entry on the timer heap. 712 // This is 0 if the timer heap is empty. 713 timer0When atomic.Int64 714 715 // The earliest known nextwhen field of a timer with 716 // timerModifiedEarlier status. Because the timer may have been 717 // modified again, there need not be any timer with this value. 718 // This is 0 if there are no timerModifiedEarlier timers. 719 timerModifiedEarliest atomic.Int64 720 721 // Per-P GC state 722 gcAssistTime int64 // Nanoseconds in assistAlloc 723 gcFractionalMarkTime int64 // Nanoseconds in fractional mark worker (atomic) 724 725 // limiterEvent tracks events for the GC CPU limiter. 726 limiterEvent limiterEvent 727 728 // gcMarkWorkerMode is the mode for the next mark worker to run in. 729 // That is, this is used to communicate with the worker goroutine 730 // selected for immediate execution by 731 // gcController.findRunnableGCWorker. When scheduling other goroutines, 732 // this field must be set to gcMarkWorkerNotWorker. 733 gcMarkWorkerMode gcMarkWorkerMode 734 // gcMarkWorkerStartTime is the nanotime() at which the most recent 735 // mark worker started. 736 gcMarkWorkerStartTime int64 737 738 // gcw is this P's GC work buffer cache. The work buffer is 739 // filled by write barriers, drained by mutator assists, and 740 // disposed on certain GC state transitions. 741 gcw gcWork 742 743 // wbBuf is this P's GC write barrier buffer. 744 // 745 // TODO: Consider caching this in the running G. 746 wbBuf wbBuf 747 748 runSafePointFn uint32 // if 1, run sched.safePointFn at next safe point 749 750 // statsSeq is a counter indicating whether this P is currently 751 // writing any stats. Its value is even when not, odd when it is. 752 statsSeq atomic.Uint32 753 754 // Lock for timers. We normally access the timers while running 755 // on this P, but the scheduler can also do it from a different P. 756 timersLock mutex 757 758 // Actions to take at some time. This is used to implement the 759 // standard library's time package. 760 // Must hold timersLock to access. 761 timers []*timer 762 763 // Number of timers in P's heap. 764 numTimers atomic.Uint32 765 766 // Number of timerDeleted timers in P's heap. 767 deletedTimers atomic.Uint32 768 769 // Race context used while executing timer functions. 770 timerRaceCtx uintptr 771 772 // maxStackScanDelta accumulates the amount of stack space held by 773 // live goroutines (i.e. those eligible for stack scanning). 774 // Flushed to gcController.maxStackScan once maxStackScanSlack 775 // or -maxStackScanSlack is reached. 776 maxStackScanDelta int64 777 778 // gc-time statistics about current goroutines 779 // Note that this differs from maxStackScan in that this 780 // accumulates the actual stack observed to be used at GC time (hi - sp), 781 // not an instantaneous measure of the total stack size that might need 782 // to be scanned (hi - lo). 783 scannedStackSize uint64 // stack size of goroutines scanned by this P 784 scannedStacks uint64 // number of goroutines scanned by this P 785 786 // preempt is set to indicate that this P should be enter the 787 // scheduler ASAP (regardless of what G is running on it). 788 preempt bool 789 790 // pageTraceBuf is a buffer for writing out page allocation/free/scavenge traces. 791 // 792 // Used only if GOEXPERIMENT=pagetrace. 793 pageTraceBuf pageTraceBuf 794 795 // Padding is no longer needed. False sharing is now not a worry because p is large enough 796 // that its size class is an integer multiple of the cache line size (for any of our architectures). 797 } 798 799 type schedt struct { 800 goidgen atomic.Uint64 801 lastpoll atomic.Int64 // time of last network poll, 0 if currently polling 802 pollUntil atomic.Int64 // time to which current poll is sleeping 803 804 lock mutex 805 806 // When increasing nmidle, nmidlelocked, nmsys, or nmfreed, be 807 // sure to call checkdead(). 808 809 midle muintptr // idle m's waiting for work 810 nmidle int32 // number of idle m's waiting for work 811 nmidlelocked int32 // number of locked m's waiting for work 812 mnext int64 // number of m's that have been created and next M ID 813 maxmcount int32 // maximum number of m's allowed (or die) 814 nmsys int32 // number of system m's not counted for deadlock 815 nmfreed int64 // cumulative number of freed m's 816 817 ngsys atomic.Int32 // number of system goroutines 818 819 pidle puintptr // idle p's 820 npidle atomic.Int32 821 nmspinning atomic.Int32 // See "Worker thread parking/unparking" comment in proc.go. 822 needspinning atomic.Uint32 // See "Delicate dance" comment in proc.go. Boolean. Must hold sched.lock to set to 1. 823 824 // Global runnable queue. 825 runq gQueue 826 runqsize int32 827 828 // disable controls selective disabling of the scheduler. 829 // 830 // Use schedEnableUser to control this. 831 // 832 // disable is protected by sched.lock. 833 disable struct { 834 // user disables scheduling of user goroutines. 835 user bool 836 runnable gQueue // pending runnable Gs 837 n int32 // length of runnable 838 } 839 840 // Global cache of dead G's. 841 gFree struct { 842 lock mutex 843 stack gList // Gs with stacks 844 noStack gList // Gs without stacks 845 n int32 846 } 847 848 // Central cache of sudog structs. 849 sudoglock mutex 850 sudogcache *sudog 851 852 // Central pool of available defer structs. 853 deferlock mutex 854 deferpool *_defer 855 856 // freem is the list of m's waiting to be freed when their 857 // m.exited is set. Linked through m.freelink. 858 freem *m 859 860 gcwaiting atomic.Bool // gc is waiting to run 861 stopwait int32 862 stopnote note 863 sysmonwait atomic.Bool 864 sysmonnote note 865 866 // safePointFn should be called on each P at the next GC 867 // safepoint if p.runSafePointFn is set. 868 safePointFn func(*p) 869 safePointWait int32 870 safePointNote note 871 872 profilehz int32 // cpu profiling rate 873 874 procresizetime int64 // nanotime() of last change to gomaxprocs 875 totaltime int64 // ∫gomaxprocs dt up to procresizetime 876 877 // sysmonlock protects sysmon's actions on the runtime. 878 // 879 // Acquire and hold this mutex to block sysmon from interacting 880 // with the rest of the runtime. 881 sysmonlock mutex 882 883 // timeToRun is a distribution of scheduling latencies, defined 884 // as the sum of time a G spends in the _Grunnable state before 885 // it transitions to _Grunning. 886 timeToRun timeHistogram 887 888 // idleTime is the total CPU time Ps have "spent" idle. 889 // 890 // Reset on each GC cycle. 891 idleTime atomic.Int64 892 893 // totalMutexWaitTime is the sum of time goroutines have spent in _Gwaiting 894 // with a waitreason of the form waitReasonSync{RW,}Mutex{R,}Lock. 895 totalMutexWaitTime atomic.Int64 896 897 // stwStoppingTimeGC/Other are distributions of stop-the-world stopping 898 // latencies, defined as the time taken by stopTheWorldWithSema to get 899 // all Ps to stop. stwStoppingTimeGC covers all GC-related STWs, 900 // stwStoppingTimeOther covers the others. 901 stwStoppingTimeGC timeHistogram 902 stwStoppingTimeOther timeHistogram 903 904 // stwTotalTimeGC/Other are distributions of stop-the-world total 905 // latencies, defined as the total time from stopTheWorldWithSema to 906 // startTheWorldWithSema. This is a superset of 907 // stwStoppingTimeGC/Other. stwTotalTimeGC covers all GC-related STWs, 908 // stwTotalTimeOther covers the others. 909 stwTotalTimeGC timeHistogram 910 stwTotalTimeOther timeHistogram 911 912 // totalRuntimeLockWaitTime (plus the value of lockWaitTime on each M in 913 // allm) is the sum of time goroutines have spent in _Grunnable and with an 914 // M, but waiting for locks within the runtime. This field stores the value 915 // for Ms that have exited. 916 totalRuntimeLockWaitTime atomic.Int64 917 } 918 919 // Values for the flags field of a sigTabT. 920 const ( 921 _SigNotify = 1 << iota // let signal.Notify have signal, even if from kernel 922 _SigKill // if signal.Notify doesn't take it, exit quietly 923 _SigThrow // if signal.Notify doesn't take it, exit loudly 924 _SigPanic // if the signal is from the kernel, panic 925 _SigDefault // if the signal isn't explicitly requested, don't monitor it 926 _SigGoExit // cause all runtime procs to exit (only used on Plan 9). 927 _SigSetStack // Don't explicitly install handler, but add SA_ONSTACK to existing libc handler 928 _SigUnblock // always unblock; see blockableSig 929 _SigIgn // _SIG_DFL action is to ignore the signal 930 ) 931 932 // Layout of in-memory per-function information prepared by linker 933 // See https://golang.org/s/go12symtab. 934 // Keep in sync with linker (../cmd/link/internal/ld/pcln.go:/pclntab) 935 // and with package debug/gosym and with symtab.go in package runtime. 936 type _func struct { 937 sys.NotInHeap // Only in static data 938 939 entryOff uint32 // start pc, as offset from moduledata.text/pcHeader.textStart 940 nameOff int32 // function name, as index into moduledata.funcnametab. 941 942 args int32 // in/out args size 943 deferreturn uint32 // offset of start of a deferreturn call instruction from entry, if any. 944 945 pcsp uint32 946 pcfile uint32 947 pcln uint32 948 npcdata uint32 949 cuOffset uint32 // runtime.cutab offset of this function's CU 950 startLine int32 // line number of start of function (func keyword/TEXT directive) 951 funcID abi.FuncID // set for certain special runtime functions 952 flag abi.FuncFlag 953 _ [1]byte // pad 954 nfuncdata uint8 // must be last, must end on a uint32-aligned boundary 955 956 // The end of the struct is followed immediately by two variable-length 957 // arrays that reference the pcdata and funcdata locations for this 958 // function. 959 960 // pcdata contains the offset into moduledata.pctab for the start of 961 // that index's table. e.g., 962 // &moduledata.pctab[_func.pcdata[_PCDATA_UnsafePoint]] is the start of 963 // the unsafe point table. 964 // 965 // An offset of 0 indicates that there is no table. 966 // 967 // pcdata [npcdata]uint32 968 969 // funcdata contains the offset past moduledata.gofunc which contains a 970 // pointer to that index's funcdata. e.g., 971 // *(moduledata.gofunc + _func.funcdata[_FUNCDATA_ArgsPointerMaps]) is 972 // the argument pointer map. 973 // 974 // An offset of ^uint32(0) indicates that there is no entry. 975 // 976 // funcdata [nfuncdata]uint32 977 } 978 979 // Pseudo-Func that is returned for PCs that occur in inlined code. 980 // A *Func can be either a *_func or a *funcinl, and they are distinguished 981 // by the first uintptr. 982 // 983 // TODO(austin): Can we merge this with inlinedCall? 984 type funcinl struct { 985 ones uint32 // set to ^0 to distinguish from _func 986 entry uintptr // entry of the real (the "outermost") frame 987 name string 988 file string 989 line int32 990 startLine int32 991 } 992 993 // layout of Itab known to compilers 994 // allocated in non-garbage-collected memory 995 // Needs to be in sync with 996 // ../cmd/compile/internal/reflectdata/reflect.go:/^func.WritePluginTable. 997 type itab struct { 998 inter *interfacetype 999 _type *_type 1000 hash uint32 // copy of _type.hash. Used for type switches. 1001 _ [4]byte 1002 fun [1]uintptr // variable sized. fun[0]==0 means _type does not implement inter. 1003 } 1004 1005 // Lock-free stack node. 1006 // Also known to export_test.go. 1007 type lfnode struct { 1008 next uint64 1009 pushcnt uintptr 1010 } 1011 1012 type forcegcstate struct { 1013 lock mutex 1014 g *g 1015 idle atomic.Bool 1016 } 1017 1018 // A _defer holds an entry on the list of deferred calls. 1019 // If you add a field here, add code to clear it in deferProcStack. 1020 // This struct must match the code in cmd/compile/internal/ssagen/ssa.go:deferstruct 1021 // and cmd/compile/internal/ssagen/ssa.go:(*state).call. 1022 // Some defers will be allocated on the stack and some on the heap. 1023 // All defers are logically part of the stack, so write barriers to 1024 // initialize them are not required. All defers must be manually scanned, 1025 // and for heap defers, marked. 1026 type _defer struct { 1027 heap bool 1028 rangefunc bool // true for rangefunc list 1029 sp uintptr // sp at time of defer 1030 pc uintptr // pc at time of defer 1031 fn func() // can be nil for open-coded defers 1032 link *_defer // next defer on G; can point to either heap or stack! 1033 1034 // If rangefunc is true, *head is the head of the atomic linked list 1035 // during a range-over-func execution. 1036 head *atomic.Pointer[_defer] 1037 } 1038 1039 // A _panic holds information about an active panic. 1040 // 1041 // A _panic value must only ever live on the stack. 1042 // 1043 // The argp and link fields are stack pointers, but don't need special 1044 // handling during stack growth: because they are pointer-typed and 1045 // _panic values only live on the stack, regular stack pointer 1046 // adjustment takes care of them. 1047 type _panic struct { 1048 argp unsafe.Pointer // pointer to arguments of deferred call run during panic; cannot move - known to liblink 1049 arg any // argument to panic 1050 link *_panic // link to earlier panic 1051 1052 // startPC and startSP track where _panic.start was called. 1053 startPC uintptr 1054 startSP unsafe.Pointer 1055 1056 // The current stack frame that we're running deferred calls for. 1057 sp unsafe.Pointer 1058 lr uintptr 1059 fp unsafe.Pointer 1060 1061 // retpc stores the PC where the panic should jump back to, if the 1062 // function last returned by _panic.next() recovers the panic. 1063 retpc uintptr 1064 1065 // Extra state for handling open-coded defers. 1066 deferBitsPtr *uint8 1067 slotsPtr unsafe.Pointer 1068 1069 recovered bool // whether this panic has been recovered 1070 goexit bool 1071 deferreturn bool 1072 } 1073 1074 // savedOpenDeferState tracks the extra state from _panic that's 1075 // necessary for deferreturn to pick up where gopanic left off, 1076 // without needing to unwind the stack. 1077 type savedOpenDeferState struct { 1078 retpc uintptr 1079 deferBitsOffset uintptr 1080 slotsOffset uintptr 1081 } 1082 1083 // ancestorInfo records details of where a goroutine was started. 1084 type ancestorInfo struct { 1085 pcs []uintptr // pcs from the stack of this goroutine 1086 goid uint64 // goroutine id of this goroutine; original goroutine possibly dead 1087 gopc uintptr // pc of go statement that created this goroutine 1088 } 1089 1090 // A waitReason explains why a goroutine has been stopped. 1091 // See gopark. Do not re-use waitReasons, add new ones. 1092 type waitReason uint8 1093 1094 const ( 1095 waitReasonZero waitReason = iota // "" 1096 waitReasonGCAssistMarking // "GC assist marking" 1097 waitReasonIOWait // "IO wait" 1098 waitReasonChanReceiveNilChan // "chan receive (nil chan)" 1099 waitReasonChanSendNilChan // "chan send (nil chan)" 1100 waitReasonDumpingHeap // "dumping heap" 1101 waitReasonGarbageCollection // "garbage collection" 1102 waitReasonGarbageCollectionScan // "garbage collection scan" 1103 waitReasonPanicWait // "panicwait" 1104 waitReasonSelect // "select" 1105 waitReasonSelectNoCases // "select (no cases)" 1106 waitReasonGCAssistWait // "GC assist wait" 1107 waitReasonGCSweepWait // "GC sweep wait" 1108 waitReasonGCScavengeWait // "GC scavenge wait" 1109 waitReasonChanReceive // "chan receive" 1110 waitReasonChanSend // "chan send" 1111 waitReasonFinalizerWait // "finalizer wait" 1112 waitReasonForceGCIdle // "force gc (idle)" 1113 waitReasonSemacquire // "semacquire" 1114 waitReasonSleep // "sleep" 1115 waitReasonSyncCondWait // "sync.Cond.Wait" 1116 waitReasonSyncMutexLock // "sync.Mutex.Lock" 1117 waitReasonSyncRWMutexRLock // "sync.RWMutex.RLock" 1118 waitReasonSyncRWMutexLock // "sync.RWMutex.Lock" 1119 waitReasonTraceReaderBlocked // "trace reader (blocked)" 1120 waitReasonWaitForGCCycle // "wait for GC cycle" 1121 waitReasonGCWorkerIdle // "GC worker (idle)" 1122 waitReasonGCWorkerActive // "GC worker (active)" 1123 waitReasonPreempted // "preempted" 1124 waitReasonDebugCall // "debug call" 1125 waitReasonGCMarkTermination // "GC mark termination" 1126 waitReasonStoppingTheWorld // "stopping the world" 1127 waitReasonFlushProcCaches // "flushing proc caches" 1128 waitReasonTraceGoroutineStatus // "trace goroutine status" 1129 waitReasonTraceProcStatus // "trace proc status" 1130 waitReasonPageTraceFlush // "page trace flush" 1131 waitReasonCoroutine // "coroutine" 1132 ) 1133 1134 var waitReasonStrings = [...]string{ 1135 waitReasonZero: "", 1136 waitReasonGCAssistMarking: "GC assist marking", 1137 waitReasonIOWait: "IO wait", 1138 waitReasonChanReceiveNilChan: "chan receive (nil chan)", 1139 waitReasonChanSendNilChan: "chan send (nil chan)", 1140 waitReasonDumpingHeap: "dumping heap", 1141 waitReasonGarbageCollection: "garbage collection", 1142 waitReasonGarbageCollectionScan: "garbage collection scan", 1143 waitReasonPanicWait: "panicwait", 1144 waitReasonSelect: "select", 1145 waitReasonSelectNoCases: "select (no cases)", 1146 waitReasonGCAssistWait: "GC assist wait", 1147 waitReasonGCSweepWait: "GC sweep wait", 1148 waitReasonGCScavengeWait: "GC scavenge wait", 1149 waitReasonChanReceive: "chan receive", 1150 waitReasonChanSend: "chan send", 1151 waitReasonFinalizerWait: "finalizer wait", 1152 waitReasonForceGCIdle: "force gc (idle)", 1153 waitReasonSemacquire: "semacquire", 1154 waitReasonSleep: "sleep", 1155 waitReasonSyncCondWait: "sync.Cond.Wait", 1156 waitReasonSyncMutexLock: "sync.Mutex.Lock", 1157 waitReasonSyncRWMutexRLock: "sync.RWMutex.RLock", 1158 waitReasonSyncRWMutexLock: "sync.RWMutex.Lock", 1159 waitReasonTraceReaderBlocked: "trace reader (blocked)", 1160 waitReasonWaitForGCCycle: "wait for GC cycle", 1161 waitReasonGCWorkerIdle: "GC worker (idle)", 1162 waitReasonGCWorkerActive: "GC worker (active)", 1163 waitReasonPreempted: "preempted", 1164 waitReasonDebugCall: "debug call", 1165 waitReasonGCMarkTermination: "GC mark termination", 1166 waitReasonStoppingTheWorld: "stopping the world", 1167 waitReasonFlushProcCaches: "flushing proc caches", 1168 waitReasonTraceGoroutineStatus: "trace goroutine status", 1169 waitReasonTraceProcStatus: "trace proc status", 1170 waitReasonPageTraceFlush: "page trace flush", 1171 waitReasonCoroutine: "coroutine", 1172 } 1173 1174 func (w waitReason) String() string { 1175 if w < 0 || w >= waitReason(len(waitReasonStrings)) { 1176 return "unknown wait reason" 1177 } 1178 return waitReasonStrings[w] 1179 } 1180 1181 func (w waitReason) isMutexWait() bool { 1182 return w == waitReasonSyncMutexLock || 1183 w == waitReasonSyncRWMutexRLock || 1184 w == waitReasonSyncRWMutexLock 1185 } 1186 1187 var ( 1188 allm *m 1189 gomaxprocs int32 1190 ncpu int32 1191 forcegc forcegcstate 1192 sched schedt 1193 newprocs int32 1194 1195 // allpLock protects P-less reads and size changes of allp, idlepMask, 1196 // and timerpMask, and all writes to allp. 1197 allpLock mutex 1198 // len(allp) == gomaxprocs; may change at safe points, otherwise 1199 // immutable. 1200 allp []*p 1201 // Bitmask of Ps in _Pidle list, one bit per P. Reads and writes must 1202 // be atomic. Length may change at safe points. 1203 // 1204 // Each P must update only its own bit. In order to maintain 1205 // consistency, a P going idle must the idle mask simultaneously with 1206 // updates to the idle P list under the sched.lock, otherwise a racing 1207 // pidleget may clear the mask before pidleput sets the mask, 1208 // corrupting the bitmap. 1209 // 1210 // N.B., procresize takes ownership of all Ps in stopTheWorldWithSema. 1211 idlepMask pMask 1212 // Bitmask of Ps that may have a timer, one bit per P. Reads and writes 1213 // must be atomic. Length may change at safe points. 1214 timerpMask pMask 1215 1216 // Pool of GC parked background workers. Entries are type 1217 // *gcBgMarkWorkerNode. 1218 gcBgMarkWorkerPool lfstack 1219 1220 // Total number of gcBgMarkWorker goroutines. Protected by worldsema. 1221 gcBgMarkWorkerCount int32 1222 1223 // Information about what cpu features are available. 1224 // Packages outside the runtime should not use these 1225 // as they are not an external api. 1226 // Set on startup in asm_{386,amd64}.s 1227 processorVersionInfo uint32 1228 isIntel bool 1229 1230 // set by cmd/link on arm systems 1231 goarm uint8 1232 goarmsoftfp uint8 1233 ) 1234 1235 // Set by the linker so the runtime can determine the buildmode. 1236 var ( 1237 islibrary bool // -buildmode=c-shared 1238 isarchive bool // -buildmode=c-archive 1239 ) 1240 1241 // Must agree with internal/buildcfg.FramePointerEnabled. 1242 const framepointer_enabled = GOARCH == "amd64" || GOARCH == "arm64" 1243