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Diffstat (limited to 'src/runtime/chan.go')
| -rw-r--r-- | src/runtime/chan.go | 851 |
1 files changed, 851 insertions, 0 deletions
diff --git a/src/runtime/chan.go b/src/runtime/chan.go new file mode 100644 index 0000000..ff9e2a9 --- /dev/null +++ b/src/runtime/chan.go @@ -0,0 +1,851 @@ +// Copyright 2014 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package runtime + +// This file contains the implementation of Go channels. + +// Invariants: +// At least one of c.sendq and c.recvq is empty, +// except for the case of an unbuffered channel with a single goroutine +// blocked on it for both sending and receiving using a select statement, +// in which case the length of c.sendq and c.recvq is limited only by the +// size of the select statement. +// +// For buffered channels, also: +// c.qcount > 0 implies that c.recvq is empty. +// c.qcount < c.dataqsiz implies that c.sendq is empty. + +import ( + "internal/abi" + "runtime/internal/atomic" + "runtime/internal/math" + "unsafe" +) + +const ( + maxAlign = 8 + hchanSize = unsafe.Sizeof(hchan{}) + uintptr(-int(unsafe.Sizeof(hchan{}))&(maxAlign-1)) + debugChan = false +) + +type hchan struct { + qcount uint // total data in the queue + dataqsiz uint // size of the circular queue + buf unsafe.Pointer // points to an array of dataqsiz elements + elemsize uint16 + closed uint32 + elemtype *_type // element type + sendx uint // send index + recvx uint // receive index + recvq waitq // list of recv waiters + sendq waitq // list of send waiters + + // lock protects all fields in hchan, as well as several + // fields in sudogs blocked on this channel. + // + // Do not change another G's status while holding this lock + // (in particular, do not ready a G), as this can deadlock + // with stack shrinking. + lock mutex +} + +type waitq struct { + first *sudog + last *sudog +} + +//go:linkname reflect_makechan reflect.makechan +func reflect_makechan(t *chantype, size int) *hchan { + return makechan(t, size) +} + +func makechan64(t *chantype, size int64) *hchan { + if int64(int(size)) != size { + panic(plainError("makechan: size out of range")) + } + + return makechan(t, int(size)) +} + +func makechan(t *chantype, size int) *hchan { + elem := t.Elem + + // compiler checks this but be safe. + if elem.Size_ >= 1<<16 { + throw("makechan: invalid channel element type") + } + if hchanSize%maxAlign != 0 || elem.Align_ > maxAlign { + throw("makechan: bad alignment") + } + + mem, overflow := math.MulUintptr(elem.Size_, uintptr(size)) + if overflow || mem > maxAlloc-hchanSize || size < 0 { + panic(plainError("makechan: size out of range")) + } + + // Hchan does not contain pointers interesting for GC when elements stored in buf do not contain pointers. + // buf points into the same allocation, elemtype is persistent. + // SudoG's are referenced from their owning thread so they can't be collected. + // TODO(dvyukov,rlh): Rethink when collector can move allocated objects. + var c *hchan + switch { + case mem == 0: + // Queue or element size is zero. + c = (*hchan)(mallocgc(hchanSize, nil, true)) + // Race detector uses this location for synchronization. + c.buf = c.raceaddr() + case elem.PtrBytes == 0: + // Elements do not contain pointers. + // Allocate hchan and buf in one call. + c = (*hchan)(mallocgc(hchanSize+mem, nil, true)) + c.buf = add(unsafe.Pointer(c), hchanSize) + default: + // Elements contain pointers. + c = new(hchan) + c.buf = mallocgc(mem, elem, true) + } + + c.elemsize = uint16(elem.Size_) + c.elemtype = elem + c.dataqsiz = uint(size) + lockInit(&c.lock, lockRankHchan) + + if debugChan { + print("makechan: chan=", c, "; elemsize=", elem.Size_, "; dataqsiz=", size, "\n") + } + return c +} + +// chanbuf(c, i) is pointer to the i'th slot in the buffer. +func chanbuf(c *hchan, i uint) unsafe.Pointer { + return add(c.buf, uintptr(i)*uintptr(c.elemsize)) +} + +// full reports whether a send on c would block (that is, the channel is full). +// It uses a single word-sized read of mutable state, so although +// the answer is instantaneously true, the correct answer may have changed +// by the time the calling function receives the return value. +func full(c *hchan) bool { + // c.dataqsiz is immutable (never written after the channel is created) + // so it is safe to read at any time during channel operation. + if c.dataqsiz == 0 { + // Assumes that a pointer read is relaxed-atomic. + return c.recvq.first == nil + } + // Assumes that a uint read is relaxed-atomic. + return c.qcount == c.dataqsiz +} + +// entry point for c <- x from compiled code. +// +//go:nosplit +func chansend1(c *hchan, elem unsafe.Pointer) { + chansend(c, elem, true, getcallerpc()) +} + +/* + * generic single channel send/recv + * If block is not nil, + * then the protocol will not + * sleep but return if it could + * not complete. + * + * sleep can wake up with g.param == nil + * when a channel involved in the sleep has + * been closed. it is easiest to loop and re-run + * the operation; we'll see that it's now closed. + */ +func chansend(c *hchan, ep unsafe.Pointer, block bool, callerpc uintptr) bool { + if c == nil { + if !block { + return false + } + gopark(nil, nil, waitReasonChanSendNilChan, traceBlockForever, 2) + throw("unreachable") + } + + if debugChan { + print("chansend: chan=", c, "\n") + } + + if raceenabled { + racereadpc(c.raceaddr(), callerpc, abi.FuncPCABIInternal(chansend)) + } + + // Fast path: check for failed non-blocking operation without acquiring the lock. + // + // After observing that the channel is not closed, we observe that the channel is + // not ready for sending. Each of these observations is a single word-sized read + // (first c.closed and second full()). + // Because a closed channel cannot transition from 'ready for sending' to + // 'not ready for sending', even if the channel is closed between the two observations, + // they imply a moment between the two when the channel was both not yet closed + // and not ready for sending. We behave as if we observed the channel at that moment, + // and report that the send cannot proceed. + // + // It is okay if the reads are reordered here: if we observe that the channel is not + // ready for sending and then observe that it is not closed, that implies that the + // channel wasn't closed during the first observation. However, nothing here + // guarantees forward progress. We rely on the side effects of lock release in + // chanrecv() and closechan() to update this thread's view of c.closed and full(). + if !block && c.closed == 0 && full(c) { + return false + } + + var t0 int64 + if blockprofilerate > 0 { + t0 = cputicks() + } + + lock(&c.lock) + + if c.closed != 0 { + unlock(&c.lock) + panic(plainError("send on closed channel")) + } + + if sg := c.recvq.dequeue(); sg != nil { + // Found a waiting receiver. We pass the value we want to send + // directly to the receiver, bypassing the channel buffer (if any). + send(c, sg, ep, func() { unlock(&c.lock) }, 3) + return true + } + + if c.qcount < c.dataqsiz { + // Space is available in the channel buffer. Enqueue the element to send. + qp := chanbuf(c, c.sendx) + if raceenabled { + racenotify(c, c.sendx, nil) + } + typedmemmove(c.elemtype, qp, ep) + c.sendx++ + if c.sendx == c.dataqsiz { + c.sendx = 0 + } + c.qcount++ + unlock(&c.lock) + return true + } + + if !block { + unlock(&c.lock) + return false + } + + // Block on the channel. Some receiver will complete our operation for us. + gp := getg() + mysg := acquireSudog() + mysg.releasetime = 0 + if t0 != 0 { + mysg.releasetime = -1 + } + // No stack splits between assigning elem and enqueuing mysg + // on gp.waiting where copystack can find it. + mysg.elem = ep + mysg.waitlink = nil + mysg.g = gp + mysg.isSelect = false + mysg.c = c + gp.waiting = mysg + gp.param = nil + c.sendq.enqueue(mysg) + // Signal to anyone trying to shrink our stack that we're about + // to park on a channel. The window between when this G's status + // changes and when we set gp.activeStackChans is not safe for + // stack shrinking. + gp.parkingOnChan.Store(true) + gopark(chanparkcommit, unsafe.Pointer(&c.lock), waitReasonChanSend, traceBlockChanSend, 2) + // Ensure the value being sent is kept alive until the + // receiver copies it out. The sudog has a pointer to the + // stack object, but sudogs aren't considered as roots of the + // stack tracer. + KeepAlive(ep) + + // someone woke us up. + if mysg != gp.waiting { + throw("G waiting list is corrupted") + } + gp.waiting = nil + gp.activeStackChans = false + closed := !mysg.success + gp.param = nil + if mysg.releasetime > 0 { + blockevent(mysg.releasetime-t0, 2) + } + mysg.c = nil + releaseSudog(mysg) + if closed { + if c.closed == 0 { + throw("chansend: spurious wakeup") + } + panic(plainError("send on closed channel")) + } + return true +} + +// send processes a send operation on an empty channel c. +// The value ep sent by the sender is copied to the receiver sg. +// The receiver is then woken up to go on its merry way. +// Channel c must be empty and locked. send unlocks c with unlockf. +// sg must already be dequeued from c. +// ep must be non-nil and point to the heap or the caller's stack. +func send(c *hchan, sg *sudog, ep unsafe.Pointer, unlockf func(), skip int) { + if raceenabled { + if c.dataqsiz == 0 { + racesync(c, sg) + } else { + // Pretend we go through the buffer, even though + // we copy directly. Note that we need to increment + // the head/tail locations only when raceenabled. + racenotify(c, c.recvx, nil) + racenotify(c, c.recvx, sg) + c.recvx++ + if c.recvx == c.dataqsiz { + c.recvx = 0 + } + c.sendx = c.recvx // c.sendx = (c.sendx+1) % c.dataqsiz + } + } + if sg.elem != nil { + sendDirect(c.elemtype, sg, ep) + sg.elem = nil + } + gp := sg.g + unlockf() + gp.param = unsafe.Pointer(sg) + sg.success = true + if sg.releasetime != 0 { + sg.releasetime = cputicks() + } + goready(gp, skip+1) +} + +// Sends and receives on unbuffered or empty-buffered channels are the +// only operations where one running goroutine writes to the stack of +// another running goroutine. The GC assumes that stack writes only +// happen when the goroutine is running and are only done by that +// goroutine. Using a write barrier is sufficient to make up for +// violating that assumption, but the write barrier has to work. +// typedmemmove will call bulkBarrierPreWrite, but the target bytes +// are not in the heap, so that will not help. We arrange to call +// memmove and typeBitsBulkBarrier instead. + +func sendDirect(t *_type, sg *sudog, src unsafe.Pointer) { + // src is on our stack, dst is a slot on another stack. + + // Once we read sg.elem out of sg, it will no longer + // be updated if the destination's stack gets copied (shrunk). + // So make sure that no preemption points can happen between read & use. + dst := sg.elem + typeBitsBulkBarrier(t, uintptr(dst), uintptr(src), t.Size_) + // No need for cgo write barrier checks because dst is always + // Go memory. + memmove(dst, src, t.Size_) +} + +func recvDirect(t *_type, sg *sudog, dst unsafe.Pointer) { + // dst is on our stack or the heap, src is on another stack. + // The channel is locked, so src will not move during this + // operation. + src := sg.elem + typeBitsBulkBarrier(t, uintptr(dst), uintptr(src), t.Size_) + memmove(dst, src, t.Size_) +} + +func closechan(c *hchan) { + if c == nil { + panic(plainError("close of nil channel")) + } + + lock(&c.lock) + if c.closed != 0 { + unlock(&c.lock) + panic(plainError("close of closed channel")) + } + + if raceenabled { + callerpc := getcallerpc() + racewritepc(c.raceaddr(), callerpc, abi.FuncPCABIInternal(closechan)) + racerelease(c.raceaddr()) + } + + c.closed = 1 + + var glist gList + + // release all readers + for { + sg := c.recvq.dequeue() + if sg == nil { + break + } + if sg.elem != nil { + typedmemclr(c.elemtype, sg.elem) + sg.elem = nil + } + if sg.releasetime != 0 { + sg.releasetime = cputicks() + } + gp := sg.g + gp.param = unsafe.Pointer(sg) + sg.success = false + if raceenabled { + raceacquireg(gp, c.raceaddr()) + } + glist.push(gp) + } + + // release all writers (they will panic) + for { + sg := c.sendq.dequeue() + if sg == nil { + break + } + sg.elem = nil + if sg.releasetime != 0 { + sg.releasetime = cputicks() + } + gp := sg.g + gp.param = unsafe.Pointer(sg) + sg.success = false + if raceenabled { + raceacquireg(gp, c.raceaddr()) + } + glist.push(gp) + } + unlock(&c.lock) + + // Ready all Gs now that we've dropped the channel lock. + for !glist.empty() { + gp := glist.pop() + gp.schedlink = 0 + goready(gp, 3) + } +} + +// empty reports whether a read from c would block (that is, the channel is +// empty). It uses a single atomic read of mutable state. +func empty(c *hchan) bool { + // c.dataqsiz is immutable. + if c.dataqsiz == 0 { + return atomic.Loadp(unsafe.Pointer(&c.sendq.first)) == nil + } + return atomic.Loaduint(&c.qcount) == 0 +} + +// entry points for <- c from compiled code. +// +//go:nosplit +func chanrecv1(c *hchan, elem unsafe.Pointer) { + chanrecv(c, elem, true) +} + +//go:nosplit +func chanrecv2(c *hchan, elem unsafe.Pointer) (received bool) { + _, received = chanrecv(c, elem, true) + return +} + +// chanrecv receives on channel c and writes the received data to ep. +// ep may be nil, in which case received data is ignored. +// If block == false and no elements are available, returns (false, false). +// Otherwise, if c is closed, zeros *ep and returns (true, false). +// Otherwise, fills in *ep with an element and returns (true, true). +// A non-nil ep must point to the heap or the caller's stack. +func chanrecv(c *hchan, ep unsafe.Pointer, block bool) (selected, received bool) { + // raceenabled: don't need to check ep, as it is always on the stack + // or is new memory allocated by reflect. + + if debugChan { + print("chanrecv: chan=", c, "\n") + } + + if c == nil { + if !block { + return + } + gopark(nil, nil, waitReasonChanReceiveNilChan, traceBlockForever, 2) + throw("unreachable") + } + + // Fast path: check for failed non-blocking operation without acquiring the lock. + if !block && empty(c) { + // After observing that the channel is not ready for receiving, we observe whether the + // channel is closed. + // + // Reordering of these checks could lead to incorrect behavior when racing with a close. + // For example, if the channel was open and not empty, was closed, and then drained, + // reordered reads could incorrectly indicate "open and empty". To prevent reordering, + // we use atomic loads for both checks, and rely on emptying and closing to happen in + // separate critical sections under the same lock. This assumption fails when closing + // an unbuffered channel with a blocked send, but that is an error condition anyway. + if atomic.Load(&c.closed) == 0 { + // Because a channel cannot be reopened, the later observation of the channel + // being not closed implies that it was also not closed at the moment of the + // first observation. We behave as if we observed the channel at that moment + // and report that the receive cannot proceed. + return + } + // The channel is irreversibly closed. Re-check whether the channel has any pending data + // to receive, which could have arrived between the empty and closed checks above. + // Sequential consistency is also required here, when racing with such a send. + if empty(c) { + // The channel is irreversibly closed and empty. + if raceenabled { + raceacquire(c.raceaddr()) + } + if ep != nil { + typedmemclr(c.elemtype, ep) + } + return true, false + } + } + + var t0 int64 + if blockprofilerate > 0 { + t0 = cputicks() + } + + lock(&c.lock) + + if c.closed != 0 { + if c.qcount == 0 { + if raceenabled { + raceacquire(c.raceaddr()) + } + unlock(&c.lock) + if ep != nil { + typedmemclr(c.elemtype, ep) + } + return true, false + } + // The channel has been closed, but the channel's buffer have data. + } else { + // Just found waiting sender with not closed. + if sg := c.sendq.dequeue(); sg != nil { + // Found a waiting sender. If buffer is size 0, receive value + // directly from sender. Otherwise, receive from head of queue + // and add sender's value to the tail of the queue (both map to + // the same buffer slot because the queue is full). + recv(c, sg, ep, func() { unlock(&c.lock) }, 3) + return true, true + } + } + + if c.qcount > 0 { + // Receive directly from queue + qp := chanbuf(c, c.recvx) + if raceenabled { + racenotify(c, c.recvx, nil) + } + if ep != nil { + typedmemmove(c.elemtype, ep, qp) + } + typedmemclr(c.elemtype, qp) + c.recvx++ + if c.recvx == c.dataqsiz { + c.recvx = 0 + } + c.qcount-- + unlock(&c.lock) + return true, true + } + + if !block { + unlock(&c.lock) + return false, false + } + + // no sender available: block on this channel. + gp := getg() + mysg := acquireSudog() + mysg.releasetime = 0 + if t0 != 0 { + mysg.releasetime = -1 + } + // No stack splits between assigning elem and enqueuing mysg + // on gp.waiting where copystack can find it. + mysg.elem = ep + mysg.waitlink = nil + gp.waiting = mysg + mysg.g = gp + mysg.isSelect = false + mysg.c = c + gp.param = nil + c.recvq.enqueue(mysg) + // Signal to anyone trying to shrink our stack that we're about + // to park on a channel. The window between when this G's status + // changes and when we set gp.activeStackChans is not safe for + // stack shrinking. + gp.parkingOnChan.Store(true) + gopark(chanparkcommit, unsafe.Pointer(&c.lock), waitReasonChanReceive, traceBlockChanRecv, 2) + + // someone woke us up + if mysg != gp.waiting { + throw("G waiting list is corrupted") + } + gp.waiting = nil + gp.activeStackChans = false + if mysg.releasetime > 0 { + blockevent(mysg.releasetime-t0, 2) + } + success := mysg.success + gp.param = nil + mysg.c = nil + releaseSudog(mysg) + return true, success +} + +// recv processes a receive operation on a full channel c. +// There are 2 parts: +// 1. The value sent by the sender sg is put into the channel +// and the sender is woken up to go on its merry way. +// 2. The value received by the receiver (the current G) is +// written to ep. +// +// For synchronous channels, both values are the same. +// For asynchronous channels, the receiver gets its data from +// the channel buffer and the sender's data is put in the +// channel buffer. +// Channel c must be full and locked. recv unlocks c with unlockf. +// sg must already be dequeued from c. +// A non-nil ep must point to the heap or the caller's stack. +func recv(c *hchan, sg *sudog, ep unsafe.Pointer, unlockf func(), skip int) { + if c.dataqsiz == 0 { + if raceenabled { + racesync(c, sg) + } + if ep != nil { + // copy data from sender + recvDirect(c.elemtype, sg, ep) + } + } else { + // Queue is full. Take the item at the + // head of the queue. Make the sender enqueue + // its item at the tail of the queue. Since the + // queue is full, those are both the same slot. + qp := chanbuf(c, c.recvx) + if raceenabled { + racenotify(c, c.recvx, nil) + racenotify(c, c.recvx, sg) + } + // copy data from queue to receiver + if ep != nil { + typedmemmove(c.elemtype, ep, qp) + } + // copy data from sender to queue + typedmemmove(c.elemtype, qp, sg.elem) + c.recvx++ + if c.recvx == c.dataqsiz { + c.recvx = 0 + } + c.sendx = c.recvx // c.sendx = (c.sendx+1) % c.dataqsiz + } + sg.elem = nil + gp := sg.g + unlockf() + gp.param = unsafe.Pointer(sg) + sg.success = true + if sg.releasetime != 0 { + sg.releasetime = cputicks() + } + goready(gp, skip+1) +} + +func chanparkcommit(gp *g, chanLock unsafe.Pointer) bool { + // There are unlocked sudogs that point into gp's stack. Stack + // copying must lock the channels of those sudogs. + // Set activeStackChans here instead of before we try parking + // because we could self-deadlock in stack growth on the + // channel lock. + gp.activeStackChans = true + // Mark that it's safe for stack shrinking to occur now, + // because any thread acquiring this G's stack for shrinking + // is guaranteed to observe activeStackChans after this store. + gp.parkingOnChan.Store(false) + // Make sure we unlock after setting activeStackChans and + // unsetting parkingOnChan. The moment we unlock chanLock + // we risk gp getting readied by a channel operation and + // so gp could continue running before everything before + // the unlock is visible (even to gp itself). + unlock((*mutex)(chanLock)) + return true +} + +// compiler implements +// +// select { +// case c <- v: +// ... foo +// default: +// ... bar +// } +// +// as +// +// if selectnbsend(c, v) { +// ... foo +// } else { +// ... bar +// } +func selectnbsend(c *hchan, elem unsafe.Pointer) (selected bool) { + return chansend(c, elem, false, getcallerpc()) +} + +// compiler implements +// +// select { +// case v, ok = <-c: +// ... foo +// default: +// ... bar +// } +// +// as +// +// if selected, ok = selectnbrecv(&v, c); selected { +// ... foo +// } else { +// ... bar +// } +func selectnbrecv(elem unsafe.Pointer, c *hchan) (selected, received bool) { + return chanrecv(c, elem, false) +} + +//go:linkname reflect_chansend reflect.chansend0 +func reflect_chansend(c *hchan, elem unsafe.Pointer, nb bool) (selected bool) { + return chansend(c, elem, !nb, getcallerpc()) +} + +//go:linkname reflect_chanrecv reflect.chanrecv +func reflect_chanrecv(c *hchan, nb bool, elem unsafe.Pointer) (selected bool, received bool) { + return chanrecv(c, elem, !nb) +} + +//go:linkname reflect_chanlen reflect.chanlen +func reflect_chanlen(c *hchan) int { + if c == nil { + return 0 + } + return int(c.qcount) +} + +//go:linkname reflectlite_chanlen internal/reflectlite.chanlen +func reflectlite_chanlen(c *hchan) int { + if c == nil { + return 0 + } + return int(c.qcount) +} + +//go:linkname reflect_chancap reflect.chancap +func reflect_chancap(c *hchan) int { + if c == nil { + return 0 + } + return int(c.dataqsiz) +} + +//go:linkname reflect_chanclose reflect.chanclose +func reflect_chanclose(c *hchan) { + closechan(c) +} + +func (q *waitq) enqueue(sgp *sudog) { + sgp.next = nil + x := q.last + if x == nil { + sgp.prev = nil + q.first = sgp + q.last = sgp + return + } + sgp.prev = x + x.next = sgp + q.last = sgp +} + +func (q *waitq) dequeue() *sudog { + for { + sgp := q.first + if sgp == nil { + return nil + } + y := sgp.next + if y == nil { + q.first = nil + q.last = nil + } else { + y.prev = nil + q.first = y + sgp.next = nil // mark as removed (see dequeueSudoG) + } + + // if a goroutine was put on this queue because of a + // select, there is a small window between the goroutine + // being woken up by a different case and it grabbing the + // channel locks. Once it has the lock + // it removes itself from the queue, so we won't see it after that. + // We use a flag in the G struct to tell us when someone + // else has won the race to signal this goroutine but the goroutine + // hasn't removed itself from the queue yet. + if sgp.isSelect && !sgp.g.selectDone.CompareAndSwap(0, 1) { + continue + } + + return sgp + } +} + +func (c *hchan) raceaddr() unsafe.Pointer { + // Treat read-like and write-like operations on the channel to + // happen at this address. Avoid using the address of qcount + // or dataqsiz, because the len() and cap() builtins read + // those addresses, and we don't want them racing with + // operations like close(). + return unsafe.Pointer(&c.buf) +} + +func racesync(c *hchan, sg *sudog) { + racerelease(chanbuf(c, 0)) + raceacquireg(sg.g, chanbuf(c, 0)) + racereleaseg(sg.g, chanbuf(c, 0)) + raceacquire(chanbuf(c, 0)) +} + +// Notify the race detector of a send or receive involving buffer entry idx +// and a channel c or its communicating partner sg. +// This function handles the special case of c.elemsize==0. +func racenotify(c *hchan, idx uint, sg *sudog) { + // We could have passed the unsafe.Pointer corresponding to entry idx + // instead of idx itself. However, in a future version of this function, + // we can use idx to better handle the case of elemsize==0. + // A future improvement to the detector is to call TSan with c and idx: + // this way, Go will continue to not allocating buffer entries for channels + // of elemsize==0, yet the race detector can be made to handle multiple + // sync objects underneath the hood (one sync object per idx) + qp := chanbuf(c, idx) + // When elemsize==0, we don't allocate a full buffer for the channel. + // Instead of individual buffer entries, the race detector uses the + // c.buf as the only buffer entry. This simplification prevents us from + // following the memory model's happens-before rules (rules that are + // implemented in racereleaseacquire). Instead, we accumulate happens-before + // information in the synchronization object associated with c.buf. + if c.elemsize == 0 { + if sg == nil { + raceacquire(qp) + racerelease(qp) + } else { + raceacquireg(sg.g, qp) + racereleaseg(sg.g, qp) + } + } else { + if sg == nil { + racereleaseacquire(qp) + } else { + racereleaseacquireg(sg.g, qp) + } + } +} |