// 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.
// 此文件包含Go通道的实现。
// Invariants:
// 不变量:
// 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.
// c.sendq和c.recvq中至少有一个是空的,除非是一个没有缓冲区的通道上有一个goroutine被阻塞,用于使用select语句进行发送和接收,
// 在这种情况下,c.sendq和c.recvq的长度仅受select语句的大小限制。
// For buffered channels, also:
// 对于缓冲通道,还应:
// c.qcount > 0 implies that c.recvq is empty.
// c.qcount < c.dataqsiz implies that c.sendq is empty.
// c.qcount>0表示c.recvq为空。
// c.qcount<c.dataqsiz意味着c.sendq为空。
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 队列中的总数据
dataqsiz uint // size of the circular queue 循环队列的大小
buf unsafe.Pointer // points to an array of dataqsiz elements 指向dataqsiz数组的指针
elemsize uint16 // 每个元素的大小
closed uint32 // 是否关闭
elemtype *_type // element type 元素类型
sendx uint // send index 发送索引
recvx uint // receive index 接收索引
recvq waitq // list of recv waiters 接受等待者列表
sendq waitq // list of send waiters 发送等待者列表
// lock protects all fields in hchan, as well as several
// fields in sudogs blocked on this channel.
// 锁保护hchan中的所有字段,以及在该通道上阻塞的sudogs中的几个字段。
// 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.
// 在持有该锁时,不要更改另一个G的状态(特别是,不要准备好一个G),因为这可能会导致堆栈收缩死锁。
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.
// 编译器对此进行检查,但要安全。
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.
// 当存储在buf中的元素不包含指针时,Hchan不包含GC感兴趣的指针。buf指向相同的分配,elemtype是持久的。
// SudoG是从其拥有的线程中引用的,因此无法收集它们。TODO(dvyukov,rlh):重新思考收集器何时可以移动已分配的对象。
var c *hchan
switch {
case mem == 0:
// Queue or element size is zero.
// 队列或元素大小为零。
c = (*hchan)(mallocgc(hchanSize, nil, true))
// Race detector uses this location for synchronization.
// 竞赛检测器使用此位置进行同步。
c.buf = c.raceaddr()
case elem.ptrdata == 0:
// Elements do not contain pointers. 元素不包含指针。
// Allocate hchan and buf in one call. 在一个调用中分配hchan和buf。
c = (*hchan)(mallocgc(hchanSize+mem, nil, true))
c.buf = add(unsafe.Pointer(c), hchanSize)
default:
// Elements contain pointers. 元素包含指针。
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.
// chanbuf(c,i)是指向缓冲区中第i个槽的指针。
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.
// full报告c上的发送是否会阻塞(即通道已满)。
// 它使用可变状态的单个单词大小的读取,因此,尽管答案立即为true,但在调用函数接收到返回值时,正确的答案可能已经更改。
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.
// c.dataqsiz是不可变的(在创建通道后从不写入),因此在通道操作期间的任何时候读取都是安全的。
if c.dataqsiz == 0 {
// Assumes that a pointer read is relaxed-atomic. 假设指针读取是松弛的原子。
return c.recvq.first == nil
}
// Assumes that a uint read is relaxed-atomic. 假设一个uint读取是放松的原子。
return c.qcount == c.dataqsiz
}
// entry point for c <- x from compiled code.
// 编译代码中c<-x的入口点。
//go:nosplit
func chansend1(c *hchan, elem unsafe.Pointer) {
chansend(c, elem, true, getcallerpc())
}
/*
* generic single channel send/recv
* 通用单通道发送/接收
* If block is not nil,
* then the protocol will not
* sleep but return if it could
* not complete.
* 如果块不是零,那么协议将不会休眠,但如果不能完成,则返回。
* 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.
* 当涉及睡眠的通道关闭时,sleep可以用g.param==nil唤醒。循环和重新运行操作是最容易的;我们会看到它现在已经关闭了。
*/
func chansend(c *hchan, ep unsafe.Pointer, block bool, callerpc uintptr) bool {
if c == nil {
if !block {
return false
}
gopark(nil, nil, waitReasonChanSendNilChan, traceEvGoStop, 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.
// 快速路径:在不获取锁的情况下检查失败的非阻塞操作。
// 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()).
// 在观察到通道没有关闭后,我们观察到通道还没有准备好发送。
// 这些观察结果中的每一个都是一个单词大小的读数(第一个是c.closed,第二个是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.
// 由于闭合通道无法从“准备发送”转换为“未准备发送”,即使通道在两次观测之间闭合,它们也意味着通道尚未闭合且未准备发送。
// 我们的行为就像当时观察到了通道,并报告发送无法继续。
// 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().
// 如果在这里重新排序读取,也没关系:如果我们观察到通道没有准备好发送,然后观察到它没有关闭,这意味着在第一次观察期间通道没有关闭。然而,这里没有任何东西可以保证取得进展。
// 我们依靠chanrecv()和closechan()中释放锁的副作用来更新这个线程的c.closed和full()视图。
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).
// 发现一个正在等待的接收器。我们绕过通道缓冲区(如果有的话),将要发送的值直接传递给接收器。
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.
// 通道缓冲区中有可用空间。登记要发送的元素。
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.
// 阻塞通道。某个接收器将为我们完成操作。
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.
// 在分配elem和在gp.waiting上排队mysg之间没有堆栈分割,等待copystack可以找到它。
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.
// 向任何试图缩小我们的堆栈的人发出信号,表明我们即将停在通道上。
// 当这个G的状态改变时和我们设置gp.activeStackChans时之间的窗口对于堆栈收缩是不安全的。
gp.parkingOnChan.Store(true)
gopark(chanparkcommit, unsafe.Pointer(&c.lock), waitReasonChanSend, traceEvGoBlockSend, 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.
// 确保发送的值保持活动状态,直到接收器将其复制出来。sudog有一个指向堆栈对象的指针,但sudog不被视为堆栈跟踪器的根。
KeepAlive(ep)
// someone woke us up.
// 有人把我们唤醒了。
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.
// send处理空通道c上的发送操作。
// 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.
// 发送器发送的值ep被复制到接收器sg。然后接收器被唤醒,继续它的快乐之路。通道c必须为空并锁定。
// send用unlockf解锁c。sg必须已经从c退出队列。ep必须是非nil并指向堆或调用方的堆栈。
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.
// 假设我们通过了缓冲区,即使我们直接复制。请注意,只有在启用race时,我们才需要增加头部/尾部位置。
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.
// 在无缓冲或空缓冲通道上发送和接收是一个运行goroutine写入另一个运行的goroutine的堆栈的唯一操作。
// GC假设堆栈写入仅在goroutine运行时发生,并且仅由该goroutine完成。使用写屏障足以弥补违反该假设的情况,但写屏障必须起作用。
// typedmemmove将调用bulkBarrierPreWrite,但目标字节不在堆中,所以这没有帮助。我们安排调用memmove并键入BitsBulkBarrier。
func sendDirect(t *_type, sg *sudog, src unsafe.Pointer) {
// src is on our stack, dst is a slot on another stack.
// src在我们的堆栈上,dst是另一个堆栈上的插槽。
// 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.
// 一旦我们从sg中读取sg.elem,如果目标堆栈被复制(收缩),它将不再更新。因此,请确保在读取和使用之间不会发生抢占点。
dst := sg.elem
typeBitsBulkBarrier(t, uintptr(dst), uintptr(src), t.size)
// No need for cgo write barrier checks because dst is always
// Go memory.
// 无需进行cgo写入屏障检查,因为dst始终为Go内存。
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.
// dst在我们的堆栈或堆上,src在另一个堆栈上。通道已锁定,因此src在此操作期间不会移动。
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 释放所有读取者
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) 释放所有写入者(他们会惊慌失措)
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. 准备好所有的G,现在我们已经解除了通道锁定。
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.
// empty报告从c读取是否会阻塞(即通道为空)。它使用可变状态的单个原子读取。
func empty(c *hchan) bool {
// c.dataqsiz is immutable.
// c.dataqsiz是不可变的。
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.
// 编译代码中<-c的入口点。
//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.
// chanrecv在通道c上接收并将接收到的数据写入ep。ep可以是nil,在这种情况下,接收到的数据被忽略。
// 如果block==false并且没有可用的元素,则返回(false,false)。否则,如果c是闭合的,则将*ep清零并返回(true,false)。
// 否则,在*ep中填充一个元素并返回(true,true)。非nil ep必须指向堆或调用方的堆栈。
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.
// raceenabled:不需要检查ep,因为它总是在堆栈上,或者是反射分配的新内存。
if debugChan {
print("chanrecv: chan=", c, "\n")
}
if c == nil {
if !block {
return
}
gopark(nil, nil, waitReasonChanReceiveNilChan, traceEvGoStop, 2)
throw("unreachable")
}
// Fast path: check for failed non-blocking operation without acquiring the lock.
// 快速路径:在不获取锁的情况下检查失败的非阻塞操作。
if !block && empty(c) {
// After observing that the channel is not ready for receiving, we observe whether the
// channel is closed.
// 在观察到通道没有准备好接收后,我们观察通道是否关闭。
// 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.
// 重新排序这些检查可能会导致在比赛结束时出现错误行为。例如,如果通道是打开的而不是空的,是关闭的,然后排空,
// 重新排序的读数可能会错误地指示“打开且空”。为了防止重新排序,我们对这两种检查都使用原子加载,并依靠清空和关闭在同一锁下的不同关键部分中进行。
// 当关闭一个发送阻塞的无缓冲通道时,这种假设失败了,但无论如何,这都是一种错误情况。
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.
// 由于通道无法重新打开,因此后来对通道未关闭的观察表明,在第一次观察时,通道也未关闭。我们表现得好像在那一刻观察到了频道,并报告接收无法继续。
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.
// 通道不可逆转地关闭。重新检查通道是否有任何待接收的数据,这些数据可能是在上述空检查和关闭检查之间到达的。当使用这样的发送进行比赛时,这里也需要顺序一致性。
if empty(c) {
// The channel is irreversibly closed and empty. 通道不可逆转地关闭和清空。
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. 通道已关闭,但通道的缓冲区有数据。
} else {
// Just found waiting sender with not closed. 刚找到未关闭的正在等待的发件人。
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).
// 找到一个正在等待的发件人。如果缓冲区大小为0,则直接从发送方接收值。
// 否则,从队列的头部接收并将发送方的值添加到队列的尾部(因为队列已满,所以两者都映射到同一个缓冲区插槽)。
recv(c, sg, ep, func() { unlock(&c.lock) }, 3)
return true, true
}
}
if c.qcount > 0 {
// Receive directly from queue 直接从队列接收
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. 没有可用的发送者:阻塞此通道。
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.
// 在分配elem和在gp.waiting上排队mysg之间没有堆栈分割,等待copystack可以找到它。
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.
// 向任何试图缩小我们的堆栈的人发出信号,表明我们即将停在通道上。当这个G的状态改变时和我们设置gp.activeStackChans时之间的窗口对于堆栈收缩是不安全的。
gp.parkingOnChan.Store(true)
gopark(chanparkcommit, unsafe.Pointer(&c.lock), waitReasonChanReceive, traceEvGoBlockRecv, 2)
// someone woke us up 有人把我们唤醒了
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.
// recv处理全信道c上的接收操作。有两部分:
1.发送器sg发送的值被放入通道中,发送器被唤醒,继续它的快乐之路。
2.接收器接收到的值(当前G)被写入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.
// 对于同步通道,两个值相同。对于异步通道,接收器从通道缓冲区获取数据,发送器的数据被放入通道缓冲区。通道c必须已满并锁定。
// recv用unlock f解锁c。sg必须已经从c退出队列。非零ep必须指向堆或调用方的堆栈。
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 从发送者复制数据
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.
// 队列已满。拿队列最前面的项目。使发件人将其项目排入队列的尾部。由于队列已满,所以这两个都是同一个插槽。
qp := chanbuf(c, c.recvx)
if raceenabled {
racenotify(c, c.recvx, nil)
racenotify(c, c.recvx, sg)
}
// copy data from queue to receiver 将数据从队列复制到接收者
if ep != nil {
typedmemmove(c.elemtype, ep, qp)
}
// copy data from sender to queue 将数据从发送者复制到队列
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.
// 有一些未锁定的sudog指向gp的堆栈。堆栈复制必须锁定那些sudog的通道。
// 在这里设置activeStackChans,而不是在我们尝试停车之前,因为我们可能会在通道锁上的堆栈增长中自死锁。
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.
// 标记现在发生堆栈收缩是安全的,因为任何获取该G的堆栈进行收缩的线程都保证在该存储之后观察activeStackChans。
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).
// 请确保我们在设置activeStackChans和取消设置parkingOnChan后解锁。解锁chanLock的那一刻,我们就有可能让gp为通道操作做好准备,因此gp可以在解锁可见之前(甚至对gp本身)继续运行。
unlock((*mutex)(chanLock))
return true
}
// compiler implements
// 编译器实现
// 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
// 编译器实现
// 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.chansend
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) 标记为已删除(请参阅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.
// 如果一个goroutine因为一个选择而被放在这个队列中,那么在被不同的情况唤醒的goroutine和它获取通道锁之间有一个小窗口。
// 一旦它有了锁,它就会从队列中删除自己,所以在那之后我们就看不到它了。我们在G结构中使用一个标志来告诉我们,
// 当其他人赢得了向这个goroutine发出信号的比赛时,但goroutine还没有从队列中删除自己。
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().
// 将通道上的类似读取和类似写入的操作视为在此地址发生。
// 避免使用qcount或dataqsiz的地址,因为len()和cap()内置读取这些地址,我们不希望它们与close()等操作竞争。
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.
// 将涉及缓冲区条目idx和通道c或其通信伙伴sg的发送或接收通知竞赛检测器。此函数处理c.elemsize==0的特殊情况。
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)
// 我们本可以传递与条目idx相对应的unsafe.Pointer,而不是idx本身。然而,在这个函数的未来版本中,我们可以使用idx来更好地处理elemsize==0的情况。
// 检测器的未来改进是用c和idx调用TSan:这样,Go将继续不为elemsize==0的通道分配缓冲区条目,但竞争检测器可以在引擎盖下处理多个同步对象(每个idx一个同步对象)
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.
// 当elemsize==0时,我们不会为通道分配完整的缓冲区。竞赛检测器使用c.buf作为唯一的缓冲区条目,而不是单个缓冲区条目。
// 这种简化使我们无法遵循内存模型的先发生后规则(raceleaseacquire中实现的规则)。相反,我们在与c.buf关联的同步对象中积累发生在信息之前的信息。
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)
}
}
}
【Golang1.20源码阅读】runtime/chan.go
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