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authorRuss Cox <rsc@golang.org>2014-09-08 00:08:51 -0400
committerRuss Cox <rsc@golang.org>2014-09-08 00:08:51 -0400
commit8528da672cc093d4dd06732819abc1f7b6b5a46e (patch)
tree334be80d4a4c85b77db6f6fdb67cbf0528cba5f5 /src/runtime/chan.go
parent73bcb69f272cbf34ddcc9daa56427a8683b5a95d (diff)
downloadgo-8528da672cc093d4dd06732819abc1f7b6b5a46e.tar.gz
build: move package sources from src/pkg to src
Preparation was in CL 134570043. This CL contains only the effect of 'hg mv src/pkg/* src'. For more about the move, see golang.org/s/go14nopkg.
Diffstat (limited to 'src/runtime/chan.go')
-rw-r--r--src/runtime/chan.go644
1 files changed, 644 insertions, 0 deletions
diff --git a/src/runtime/chan.go b/src/runtime/chan.go
new file mode 100644
index 000000000..91ade4d37
--- /dev/null
+++ b/src/runtime/chan.go
@@ -0,0 +1,644 @@
+// 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.
+
+import "unsafe"
+
+const (
+ maxAlign = 8
+ hchanSize = unsafe.Sizeof(hchan{}) + uintptr(-int(unsafe.Sizeof(hchan{}))&(maxAlign-1))
+ debugChan = false
+)
+
+// TODO(khr): make hchan.buf an unsafe.Pointer, not a *uint8
+
+func makechan(t *chantype, size int64) *hchan {
+ elem := t.elem
+
+ // compiler checks this but be safe.
+ if elem.size >= 1<<16 {
+ gothrow("makechan: invalid channel element type")
+ }
+ if hchanSize%maxAlign != 0 || elem.align > maxAlign {
+ gothrow("makechan: bad alignment")
+ }
+ if size < 0 || int64(uintptr(size)) != size || (elem.size > 0 && uintptr(size) > (maxMem-hchanSize)/uintptr(elem.size)) {
+ panic("makechan: size out of range")
+ }
+
+ var c *hchan
+ if elem.kind&kindNoPointers != 0 || size == 0 {
+ // Allocate memory in one call.
+ // Hchan does not contain pointers interesting for GC in this case:
+ // 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.
+ c = (*hchan)(gomallocgc(hchanSize+uintptr(size)*uintptr(elem.size), nil, flagNoScan))
+ if size > 0 && elem.size != 0 {
+ c.buf = (*uint8)(add(unsafe.Pointer(c), hchanSize))
+ } else {
+ c.buf = (*uint8)(unsafe.Pointer(c)) // race detector uses this location for synchronization
+ }
+ } else {
+ c = new(hchan)
+ c.buf = (*uint8)(newarray(elem, uintptr(size)))
+ }
+ c.elemsize = uint16(elem.size)
+ c.elemtype = elem
+ c.dataqsiz = uint(size)
+
+ if debugChan {
+ print("makechan: chan=", c, "; elemsize=", elem.size, "; elemalg=", elem.alg, "; 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(unsafe.Pointer(c.buf), uintptr(i)*uintptr(c.elemsize))
+}
+
+// entry point for c <- x from compiled code
+//go:nosplit
+func chansend1(t *chantype, c *hchan, elem unsafe.Pointer) {
+ chansend(t, c, elem, true, getcallerpc(unsafe.Pointer(&t)))
+}
+
+/*
+ * 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(t *chantype, c *hchan, ep unsafe.Pointer, block bool, callerpc uintptr) bool {
+ if raceenabled {
+ raceReadObjectPC(t.elem, ep, callerpc, funcPC(chansend))
+ }
+
+ if c == nil {
+ if !block {
+ return false
+ }
+ gopark(nil, nil, "chan send (nil chan)")
+ gothrow("unreachable")
+ }
+
+ if debugChan {
+ print("chansend: chan=", c, "\n")
+ }
+
+ if raceenabled {
+ racereadpc(unsafe.Pointer(c), callerpc, funcPC(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 c.recvq.first or c.qcount depending on kind of channel).
+ // 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.
+ if !block && c.closed == 0 && ((c.dataqsiz == 0 && c.recvq.first == nil) ||
+ (c.dataqsiz > 0 && c.qcount == c.dataqsiz)) {
+ return false
+ }
+
+ var t0 int64
+ if blockprofilerate > 0 {
+ t0 = cputicks()
+ }
+
+ lock(&c.lock)
+ if c.closed != 0 {
+ unlock(&c.lock)
+ panic("send on closed channel")
+ }
+
+ if c.dataqsiz == 0 { // synchronous channel
+ sg := c.recvq.dequeue()
+ if sg != nil { // found a waiting receiver
+ if raceenabled {
+ racesync(c, sg)
+ }
+ unlock(&c.lock)
+
+ recvg := sg.g
+ recvg.param = unsafe.Pointer(sg)
+ if sg.elem != nil {
+ memmove(unsafe.Pointer(sg.elem), ep, uintptr(c.elemsize))
+ }
+ if sg.releasetime != 0 {
+ sg.releasetime = cputicks()
+ }
+ goready(recvg)
+ return true
+ }
+
+ if !block {
+ unlock(&c.lock)
+ return false
+ }
+
+ // no receiver available: block on this channel.
+ gp := getg()
+ mysg := acquireSudog()
+ mysg.releasetime = 0
+ if t0 != 0 {
+ mysg.releasetime = -1
+ }
+ mysg.elem = ep
+ mysg.waitlink = nil
+ gp.waiting = mysg
+ mysg.g = gp
+ mysg.selectdone = nil
+ gp.param = nil
+ c.sendq.enqueue(mysg)
+ goparkunlock(&c.lock, "chan send")
+
+ // someone woke us up.
+ if gp.param == nil {
+ if c.closed == 0 {
+ gothrow("chansend: spurious wakeup")
+ }
+ panic("send on closed channel")
+ }
+ if mysg.releasetime > 0 {
+ blockevent(int64(mysg.releasetime)-t0, 2)
+ }
+ if mysg != gp.waiting {
+ gothrow("G waiting list is corrupted!")
+ }
+ gp.waiting = nil
+ releaseSudog(mysg)
+ return true
+ }
+
+ // asynchronous channel
+ // wait for some space to write our data
+ var t1 int64
+ for c.qcount >= c.dataqsiz {
+ if !block {
+ unlock(&c.lock)
+ return false
+ }
+ gp := getg()
+ mysg := acquireSudog()
+ mysg.releasetime = 0
+ if t0 != 0 {
+ mysg.releasetime = -1
+ }
+ mysg.g = gp
+ mysg.elem = nil
+ mysg.selectdone = nil
+ c.sendq.enqueue(mysg)
+ goparkunlock(&c.lock, "chan send")
+
+ // someone woke us up - try again
+ if mysg.releasetime > 0 {
+ t1 = mysg.releasetime
+ }
+ releaseSudog(mysg)
+ lock(&c.lock)
+ if c.closed != 0 {
+ unlock(&c.lock)
+ panic("send on closed channel")
+ }
+ }
+
+ // write our data into the channel buffer
+ if raceenabled {
+ raceacquire(chanbuf(c, c.sendx))
+ racerelease(chanbuf(c, c.sendx))
+ }
+ memmove(chanbuf(c, c.sendx), ep, uintptr(c.elemsize))
+ c.sendx++
+ if c.sendx == c.dataqsiz {
+ c.sendx = 0
+ }
+ c.qcount++
+
+ // wake up a waiting receiver
+ sg := c.recvq.dequeue()
+ if sg != nil {
+ recvg := sg.g
+ unlock(&c.lock)
+ if sg.releasetime != 0 {
+ sg.releasetime = cputicks()
+ }
+ goready(recvg)
+ } else {
+ unlock(&c.lock)
+ }
+ if t1 > 0 {
+ blockevent(t1-t0, 2)
+ }
+ return true
+}
+
+func closechan(c *hchan) {
+ if c == nil {
+ panic("close of nil channel")
+ }
+
+ lock(&c.lock)
+ if c.closed != 0 {
+ unlock(&c.lock)
+ panic("close of closed channel")
+ }
+
+ if raceenabled {
+ callerpc := getcallerpc(unsafe.Pointer(&c))
+ racewritepc(unsafe.Pointer(c), callerpc, funcPC(closechan))
+ racerelease(unsafe.Pointer(c))
+ }
+
+ c.closed = 1
+
+ // release all readers
+ for {
+ sg := c.recvq.dequeue()
+ if sg == nil {
+ break
+ }
+ gp := sg.g
+ gp.param = nil
+ if sg.releasetime != 0 {
+ sg.releasetime = cputicks()
+ }
+ goready(gp)
+ }
+
+ // release all writers
+ for {
+ sg := c.sendq.dequeue()
+ if sg == nil {
+ break
+ }
+ gp := sg.g
+ gp.param = nil
+ if sg.releasetime != 0 {
+ sg.releasetime = cputicks()
+ }
+ goready(gp)
+ }
+ unlock(&c.lock)
+}
+
+// entry points for <- c from compiled code
+//go:nosplit
+func chanrecv1(t *chantype, c *hchan, elem unsafe.Pointer) {
+ chanrecv(t, c, elem, true)
+}
+
+//go:nosplit
+func chanrecv2(t *chantype, c *hchan, elem unsafe.Pointer) (received bool) {
+ _, received = chanrecv(t, 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).
+func chanrecv(t *chantype, c *hchan, ep unsafe.Pointer, block bool) (selected, received bool) {
+ // raceenabled: don't need to check ep, as it is always on the stack.
+
+ if debugChan {
+ print("chanrecv: chan=", c, "\n")
+ }
+
+ if c == nil {
+ if !block {
+ return
+ }
+ gopark(nil, nil, "chan receive (nil chan)")
+ gothrow("unreachable")
+ }
+
+ // Fast path: check for failed non-blocking operation without acquiring the lock.
+ //
+ // After observing that the channel is not ready for receiving, we observe that the
+ // channel is not closed. Each of these observations is a single word-sized read
+ // (first c.sendq.first or c.qcount, and second c.closed).
+ // 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.
+ //
+ // The order of operations is important here: reversing the operations can lead to
+ // incorrect behavior when racing with a close.
+ if !block && (c.dataqsiz == 0 && c.sendq.first == nil ||
+ c.dataqsiz > 0 && atomicloaduint(&c.qcount) == 0) &&
+ atomicload(&c.closed) == 0 {
+ return
+ }
+
+ var t0 int64
+ if blockprofilerate > 0 {
+ t0 = cputicks()
+ }
+
+ lock(&c.lock)
+ if c.dataqsiz == 0 { // synchronous channel
+ if c.closed != 0 {
+ return recvclosed(c, ep)
+ }
+
+ sg := c.sendq.dequeue()
+ if sg != nil {
+ if raceenabled {
+ racesync(c, sg)
+ }
+ unlock(&c.lock)
+
+ if ep != nil {
+ memmove(ep, sg.elem, uintptr(c.elemsize))
+ }
+ gp := sg.g
+ gp.param = unsafe.Pointer(sg)
+ if sg.releasetime != 0 {
+ sg.releasetime = cputicks()
+ }
+ goready(gp)
+ selected = true
+ received = true
+ return
+ }
+
+ if !block {
+ unlock(&c.lock)
+ return
+ }
+
+ // no sender available: block on this channel.
+ gp := getg()
+ mysg := acquireSudog()
+ mysg.releasetime = 0
+ if t0 != 0 {
+ mysg.releasetime = -1
+ }
+ mysg.elem = ep
+ mysg.waitlink = nil
+ gp.waiting = mysg
+ mysg.g = gp
+ mysg.selectdone = nil
+ gp.param = nil
+ c.recvq.enqueue(mysg)
+ goparkunlock(&c.lock, "chan receive")
+
+ // someone woke us up
+ gp.waiting = nil
+ if mysg.releasetime > 0 {
+ blockevent(mysg.releasetime-t0, 2)
+ }
+ releaseSudog(mysg)
+
+ if gp.param != nil {
+ // a sender sent us some data. It already wrote to ep.
+ selected = true
+ received = true
+ return
+ }
+
+ lock(&c.lock)
+ if c.closed == 0 {
+ gothrow("chanrecv: spurious wakeup")
+ }
+ return recvclosed(c, ep)
+ }
+
+ // asynchronous channel
+ // wait for some data to appear
+ var t1 int64
+ for c.qcount <= 0 {
+ if c.closed != 0 {
+ selected, received = recvclosed(c, ep)
+ if t1 > 0 {
+ blockevent(t1-t0, 2)
+ }
+ return
+ }
+
+ if !block {
+ unlock(&c.lock)
+ return
+ }
+
+ // wait for someone to send an element
+ gp := getg()
+ mysg := acquireSudog()
+ mysg.releasetime = 0
+ if t0 != 0 {
+ mysg.releasetime = -1
+ }
+ mysg.elem = nil
+ mysg.g = gp
+ mysg.selectdone = nil
+
+ c.recvq.enqueue(mysg)
+ goparkunlock(&c.lock, "chan receive")
+
+ // someone woke us up - try again
+ if mysg.releasetime > 0 {
+ t1 = mysg.releasetime
+ }
+ releaseSudog(mysg)
+ lock(&c.lock)
+ }
+
+ if raceenabled {
+ raceacquire(chanbuf(c, c.recvx))
+ racerelease(chanbuf(c, c.recvx))
+ }
+ if ep != nil {
+ memmove(ep, chanbuf(c, c.recvx), uintptr(c.elemsize))
+ }
+ memclr(chanbuf(c, c.recvx), uintptr(c.elemsize))
+
+ c.recvx++
+ if c.recvx == c.dataqsiz {
+ c.recvx = 0
+ }
+ c.qcount--
+
+ // ping a sender now that there is space
+ sg := c.sendq.dequeue()
+ if sg != nil {
+ gp := sg.g
+ unlock(&c.lock)
+ if sg.releasetime != 0 {
+ sg.releasetime = cputicks()
+ }
+ goready(gp)
+ } else {
+ unlock(&c.lock)
+ }
+
+ if t1 > 0 {
+ blockevent(t1-t0, 2)
+ }
+ selected = true
+ received = true
+ return
+}
+
+// recvclosed is a helper function for chanrecv. Handles cleanup
+// when the receiver encounters a closed channel.
+// Caller must hold c.lock, recvclosed will release the lock.
+func recvclosed(c *hchan, ep unsafe.Pointer) (selected, recevied bool) {
+ if raceenabled {
+ raceacquire(unsafe.Pointer(c))
+ }
+ unlock(&c.lock)
+ if ep != nil {
+ memclr(ep, uintptr(c.elemsize))
+ }
+ return true, false
+}
+
+// compiler implements
+//
+// select {
+// case c <- v:
+// ... foo
+// default:
+// ... bar
+// }
+//
+// as
+//
+// if selectnbsend(c, v) {
+// ... foo
+// } else {
+// ... bar
+// }
+//
+func selectnbsend(t *chantype, c *hchan, elem unsafe.Pointer) (selected bool) {
+ return chansend(t, c, elem, false, getcallerpc(unsafe.Pointer(&t)))
+}
+
+// compiler implements
+//
+// select {
+// case v = <-c:
+// ... foo
+// default:
+// ... bar
+// }
+//
+// as
+//
+// if selectnbrecv(&v, c) {
+// ... foo
+// } else {
+// ... bar
+// }
+//
+func selectnbrecv(t *chantype, elem unsafe.Pointer, c *hchan) (selected bool) {
+ selected, _ = chanrecv(t, c, elem, false)
+ return
+}
+
+// compiler implements
+//
+// select {
+// case v, ok = <-c:
+// ... foo
+// default:
+// ... bar
+// }
+//
+// as
+//
+// if c != nil && selectnbrecv2(&v, &ok, c) {
+// ... foo
+// } else {
+// ... bar
+// }
+//
+func selectnbrecv2(t *chantype, elem unsafe.Pointer, received *bool, c *hchan) (selected bool) {
+ // TODO(khr): just return 2 values from this function, now that it is in Go.
+ selected, *received = chanrecv(t, c, elem, false)
+ return
+}
+
+func reflect_chansend(t *chantype, c *hchan, elem unsafe.Pointer, nb bool) (selected bool) {
+ return chansend(t, c, elem, !nb, getcallerpc(unsafe.Pointer(&t)))
+}
+
+func reflect_chanrecv(t *chantype, c *hchan, nb bool, elem unsafe.Pointer) (selected bool, received bool) {
+ return chanrecv(t, c, elem, !nb)
+}
+
+func reflect_chanlen(c *hchan) int {
+ if c == nil {
+ return 0
+ }
+ return int(c.qcount)
+}
+
+func reflect_chancap(c *hchan) int {
+ if c == nil {
+ return 0
+ }
+ return int(c.dataqsiz)
+}
+
+func (q *waitq) enqueue(sgp *sudog) {
+ sgp.next = nil
+ if q.first == nil {
+ q.first = sgp
+ q.last = sgp
+ return
+ }
+ q.last.next = sgp
+ q.last = sgp
+}
+
+func (q *waitq) dequeue() *sudog {
+ for {
+ sgp := q.first
+ if sgp == nil {
+ return nil
+ }
+ q.first = sgp.next
+ if q.last == sgp {
+ q.last = nil
+ }
+
+ // if sgp participates in a select and is already signaled, ignore it
+ if sgp.selectdone != nil {
+ // claim the right to signal
+ if *sgp.selectdone != 0 || !cas(sgp.selectdone, 0, 1) {
+ continue
+ }
+ }
+
+ return sgp
+ }
+}
+
+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))
+}