internal/poll: don't return from Close until descriptor is closed

This permits the program to reliably know that when the Close method
returns, the descriptor has definitely been closed. This matters at
least for listeners.

Fixes #21856
Updates #7970

Change-Id: I1fd0cfd2333649e6e67c6ae956e19fdff3a35a83
Reviewed-on: https://go-review.googlesource.com/66150
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Joe Tsai <joetsai@google.com>

diff --git a/src/internal/poll/fd_unix.go b/src/internal/poll/fd_unix.go
index d9538e364b3a73817899ea93c4b5bec9b3e2f2bf..c51370a682470b399dfdd1c6efec247e3da23ac2 100644 (file)
--- a/src/internal/poll/fd_unix.go
+++ b/src/internal/poll/fd_unix.go
@@ -26,6 +26,9 @@ type FD struct {
        // Writev cache.
        iovecs *[]syscall.Iovec
 
+       // Semaphore signaled when file is closed.
+       csema uint32
+
        // Whether this is a streaming descriptor, as opposed to a
        // packet-based descriptor like a UDP socket. Immutable.
        IsStream bool
@@ -62,6 +65,7 @@ func (fd *FD) destroy() error {
        fd.pd.close()
        err := CloseFunc(fd.Sysfd)
        fd.Sysfd = -1
+       runtime_Semrelease(&fd.csema)
        return err
 }
 
@@ -79,7 +83,11 @@ func (fd *FD) Close() error {
        fd.pd.evict()
        // The call to decref will call destroy if there are no other
        // references.
-       return fd.decref()
+       err := fd.decref()
+       // Wait until the descriptor is closed. If this was the only
+       // reference, it is already closed.
+       runtime_Semacquire(&fd.csema)
+       return err
 }
 
 // Shutdown wraps the shutdown network call.

diff --git a/src/internal/poll/fd_windows.go b/src/internal/poll/fd_windows.go
index b0991a29f237745cda8a498032c1363c6ea13ed4..5118e3f7690d2febe013ce7b6650cf67337dd9d7 100644 (file)
--- a/src/internal/poll/fd_windows.go
+++ b/src/internal/poll/fd_windows.go
@@ -278,6 +278,9 @@ type FD struct {
        readbyte       []byte   // buffer to hold decoding of readuint16 from utf16 to utf8
        readbyteOffset int      // readbyte[readOffset:] is yet to be consumed with file.Read
 
+       // Semaphore signaled when file is closed.
+       csema uint32
+
        skipSyncNotif bool
 
        // Whether this is a streaming descriptor, as opposed to a
@@ -399,6 +402,7 @@ func (fd *FD) destroy() error {
                err = CloseFunc(fd.Sysfd)
        }
        fd.Sysfd = syscall.InvalidHandle
+       runtime_Semrelease(&fd.csema)
        return err
 }
 
@@ -410,7 +414,11 @@ func (fd *FD) Close() error {
        }
        // unblock pending reader and writer
        fd.pd.evict()
-       return fd.decref()
+       err := fd.decref()
+       // Wait until the descriptor is closed. If this was the only
+       // reference, it is already closed.
+       runtime_Semacquire(&fd.csema)
+       return err
 }
 
 // Shutdown wraps the shutdown network call.

diff --git a/src/net/listen_test.go b/src/net/listen_test.go
index 21ad4462f68f16355027b2259fa1b795a417a849..63fb144fdc16be6342c39eb39e82aeaea9b697d5 100644 (file)
--- a/src/net/listen_test.go
+++ b/src/net/listen_test.go
@@ -13,6 +13,7 @@ import (
        "runtime"
        "syscall"
        "testing"
+       "time"
 )
 
 func (ln *TCPListener) port() string {
@@ -696,3 +697,34 @@ func multicastRIBContains(ip IP) (bool, error) {
        }
        return false, nil
 }
+
+// Issue 21856.
+func TestClosingListener(t *testing.T) {
+       listener, err := Listen("tcp", ":0")
+       if err != nil {
+               t.Fatal(err)
+       }
+       addr := listener.Addr()
+
+       go func() {
+               for {
+                       c, err := listener.Accept()
+                       if err != nil {
+                               return
+                       }
+                       c.Close()
+               }
+       }()
+
+       // Let the goroutine start. We don't sleep long: if the
+       // goroutine doesn't start, the test will pass without really
+       // testing anything, which is OK.
+       time.Sleep(time.Millisecond)
+
+       listener.Close()
+
+       _, err = Listen("tcp", addr.String())
+       if err != nil {
+               t.Error(err)
+       }
+}