runtime: add netpollBreak

The new netpollBreak function can be used to interrupt a blocking netpoll.
This function is not currently used; it will be used by later CLs.

Updates #27707

Change-Id: I5cb936609ba13c3c127ea1368a49194fc58c9f4d
Reviewed-on: https://go-review.googlesource.com/c/go/+/171824
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

1 files changed, 14 insertions, 8 deletions

diff --git a/src/runtime/netpoll_aix.go b/src/runtime/netpoll_aix.go
index 6feda27b80..e1512f826c 100644
--- a/src/runtime/netpoll_aix.go
+++ b/src/runtime/netpoll_aix.go
@@ -63,12 +63,8 @@ func netpollinit() {
 	pds[0] = nil
 }
 
-func netpolldescriptor() uintptr {
-	// Both fd must be returned
-	if rdwake > 0xFFFF || wrwake > 0xFFFF {
-		throw("netpolldescriptor: invalid fd number")
-	}
-	return uintptr(rdwake<<16 | wrwake)
+func netpollIsPollDescriptor(fd uintptr) bool {
+	return fd == uintptr(rdwake) || fd == uintptr(wrwake)
 }
 
 // netpollwakeup writes on wrwake to wakeup poll before any changes.
@@ -132,6 +128,11 @@ func netpollarm(pd *pollDesc, mode int) {
 	unlock(&mtxset)
 }
 
+// netpollBreak interrupts an epollwait.
+func netpollBreak() {
+	netpollwakeup()
+}
+
 // netpoll checks for ready network connections.
 // Returns list of goroutines that become runnable.
 // delay < 0: blocks indefinitely
@@ -176,8 +177,13 @@ retry:
 	}
 	// Check if some descriptors need to be changed
 	if n != 0 && pfds[0].revents&(_POLLIN|_POLLHUP|_POLLERR) != 0 {
-		var b [1]byte
-		for read(rdwake, unsafe.Pointer(&b[0]), 1) == 1 {
+		if delay != 0 {
+			// A netpollwakeup could be picked up by a
+			// non-blocking poll. Only clear the wakeup
+			// if blocking.
+			var b [1]byte
+			for read(rdwake, unsafe.Pointer(&b[0]), 1) == 1 {
+			}
 		}
 		// Do not look at the other fds in this case as the mode may have changed
 		// XXX only additions of flags are made, so maybe it is ok