runtime: change netpoll to take an amount of time to block

This new facility will be used by future CLs in this series.

Change the only blocking call to netpoll to do the right thing when
netpoll returns an empty list.

Updates #6239
Updates #27707

Change-Id: I58b3c2903eda61a3698b1a4729ed0e81382bb1ed
Reviewed-on: https://go-review.googlesource.com/c/go/+/171821
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

1 files changed, 21 insertions, 12 deletions

diff --git a/src/runtime/netpoll_windows.go b/src/runtime/netpoll_windows.go
index 07ef15ce2f..fde413677a 100644
--- a/src/runtime/netpoll_windows.go
+++ b/src/runtime/netpoll_windows.go
@@ -61,9 +61,12 @@ func netpollarm(pd *pollDesc, mode int) {
 	throw("runtime: unused")
 }
 
-// Polls for completed network IO.
+// netpoll checks for ready network connections.
 // Returns list of goroutines that become runnable.
-func netpoll(block bool) gList {
+// delay < 0: blocks indefinitely
+// delay == 0: does not block, just polls
+// delay > 0: block for up to that many nanoseconds
+func netpoll(delay int64) gList {
 	var entries [64]overlappedEntry
 	var wait, qty, key, flags, n, i uint32
 	var errno int32
@@ -75,23 +78,32 @@ func netpoll(block bool) gList {
 	if iocphandle == _INVALID_HANDLE_VALUE {
 		return gList{}
 	}
-	wait = 0
-	if block {
+	if delay < 0 {
 		wait = _INFINITE
+	} else if delay == 0 {
+		wait = 0
+	} else if delay < 1e6 {
+		wait = 1
+	} else if delay < 1e15 {
+		wait = uint32(delay / 1e6)
+	} else {
+		// An arbitrary cap on how long to wait for a timer.
+		// 1e9 ms == ~11.5 days.
+		wait = 1e9
 	}
-retry:
+
 	if _GetQueuedCompletionStatusEx != nil {
 		n = uint32(len(entries) / int(gomaxprocs))
 		if n < 8 {
 			n = 8
 		}
-		if block {
+		if delay != 0 {
 			mp.blocked = true
 		}
 		if stdcall6(_GetQueuedCompletionStatusEx, iocphandle, uintptr(unsafe.Pointer(&entries[0])), uintptr(n), uintptr(unsafe.Pointer(&n)), uintptr(wait), 0) == 0 {
 			mp.blocked = false
 			errno = int32(getlasterror())
-			if !block && errno == _WAIT_TIMEOUT {
+			if errno == _WAIT_TIMEOUT {
 				return gList{}
 			}
 			println("runtime: GetQueuedCompletionStatusEx failed (errno=", errno, ")")
@@ -111,13 +123,13 @@ retry:
 		op = nil
 		errno = 0
 		qty = 0
-		if block {
+		if delay != 0 {
 			mp.blocked = true
 		}
 		if stdcall5(_GetQueuedCompletionStatus, iocphandle, uintptr(unsafe.Pointer(&qty)), uintptr(unsafe.Pointer(&key)), uintptr(unsafe.Pointer(&op)), uintptr(wait)) == 0 {
 			mp.blocked = false
 			errno = int32(getlasterror())
-			if !block && errno == _WAIT_TIMEOUT {
+			if errno == _WAIT_TIMEOUT {
 				return gList{}
 			}
 			if op == nil {
@@ -129,9 +141,6 @@ retry:
 		mp.blocked = false
 		handlecompletion(&toRun, op, errno, qty)
 	}
-	if block && toRun.empty() {
-		goto retry
-	}
 	return toRun
 }