Use close$NOCANCEL on the Mac

base/mac/close_nocancel.cc

+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// http://crbug.com/269623
+// http://openradar.appspot.com/14999594
+//
+// When the default version of close used on Mac OS X fails with EINTR, the
+// file descriptor is not in a deterministic state. It may have been closed,
+// or it may not have been. This makes it impossible to gracefully recover
+// from the error. If the close is retried after the FD has been closed, the
+// subsequent close can report EBADF, or worse, it can close an unrelated FD
+// opened by another thread. If the close is not retried after the FD has been
+// left open, the FD is leaked. Neither of these are good options.
+//
+// Mac OS X provides an alternate version of close, close$NOCANCEL. This
+// version will never fail with EINTR before the FD is actually closed. With
+// this version, it is thus safe to call close without checking for EINTR (as
+// the HANDLE_EINTR macro does) and not risk leaking the FD. In fact, mixing
+// this verison of close with HANDLE_EINTR is hazardous.
+//
+// The $NOCANCEL variants of various system calls are activated by compiling
+// with __DARWIN_NON_CANCELABLE, which prevents them from being pthread
+// cancellation points. Rather than taking such a heavy-handed approach, this
+// file implements an alternative: to use the $NOCANCEL variant of close (thus
+// preventing it from being a pthread cancellation point) without affecting
+// any other system calls.
+//
+// This file operates by providing a close function with the non-$NOCANCEL
+// symbol name expected for the compilation environment as set by <unistd.h>
+// and <sys/cdefs.h> (the DARWIN_ALIAS_C macro). That function calls the
+// $NOCANCEL variant, which is resolved from libsyscall. By linking with this
+// version of close prior to the libsyscall version, close's implementation is
+// overridden.
+
+#include <sys/cdefs.h>
+
+// If the non-cancelable variants of all system calls have already been
+// chosen, do nothing.
+#if !__DARWIN_NON_CANCELABLE
+
+extern "C" {
+
+#if __DARWIN_UNIX03 && !__DARWIN_ONLY_UNIX_CONFORMANCE
+
+// When there's a choice between UNIX2003 and pre-UNIX2003 and UNIX2003 has
+// been chosen:
+#define close_interface close$UNIX2003
+#define close_implementation close$NOCANCEL$UNIX2003
+
+#elif !__DARWIN_UNIX03 && !__DARWIN_ONLY_UNIX_CONFORMANCE
+
+// When there's a choice between UNIX2003 and pre-UNIX2003 and pre-UNIX2003
+// has been chosen. There's no close$NOCANCEL symbol in this case, so use
+// close$NOCANCEL$UNIX2003 as the implementation. It does the same thing
+// that close$NOCANCEL would do.
+#define close_interface close
+#define close_implementation close$NOCANCEL$UNIX2003
+
+#else  // __DARWIN_ONLY_UNIX_CONFORMANCE
+
+// When only UNIX2003 is supported:
+#define close_interface close
+#define close_implementation close$NOCANCEL
+
+#endif
+
+int close_implementation(int fd);
+
+int close_interface(int fd) {
+  return close_implementation(fd);
+}
+
+#undef close_interface
+#undef close_implementation
+
+}  // extern "C"
+
+#endif  // !__DARWIN_NON_CANCELABLE