base/mac/close_nocancel.cc

   1 // Copyright 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 // http://crbug.com/269623
   6 // http://openradar.appspot.com/14999594
   7 //
   8 // When the default version of close used on Mac OS X fails with EINTR, the
   9 // file descriptor is not in a deterministic state. It may have been closed,
  10 // or it may not have been. This makes it impossible to gracefully recover
  11 // from the error. If the close is retried after the FD has been closed, the
  12 // subsequent close can report EBADF, or worse, it can close an unrelated FD
  13 // opened by another thread. If the close is not retried after the FD has been
  14 // left open, the FD is leaked. Neither of these are good options.
  15 //
  16 // Mac OS X provides an alternate version of close, close$NOCANCEL. This
  17 // version will never fail with EINTR before the FD is actually closed. With
  18 // this version, it is thus safe to call close without checking for EINTR (as
  19 // the HANDLE_EINTR macro does) and not risk leaking the FD. In fact, mixing
  20 // this verison of close with HANDLE_EINTR is hazardous.
  21 //
  22 // The $NOCANCEL variants of various system calls are activated by compiling
  23 // with __DARWIN_NON_CANCELABLE, which prevents them from being pthread
  24 // cancellation points. Rather than taking such a heavy-handed approach, this
  25 // file implements an alternative: to use the $NOCANCEL variant of close (thus
  26 // preventing it from being a pthread cancellation point) without affecting
  27 // any other system calls.
  28 //
  29 // This file operates by providing a close function with the non-$NOCANCEL
  30 // symbol name expected for the compilation environment as set by <unistd.h>
  31 // and <sys/cdefs.h> (the DARWIN_ALIAS_C macro). That name is set by an asm
  32 // label on the declaration of the close function, so the definition of that
  33 // function receives that name. The function calls the $NOCANCEL variant, which
  34 // is resolved from libsyscall. By linking with this version of close prior to
  35 // the libsyscall version, close's implementation is overridden.
  36
  37 #include <sys/cdefs.h>
  38 #include <unistd.h>
  39
  40 // If the non-cancelable variants of all system calls have already been
  41 // chosen, do nothing.
  42 #if !__DARWIN_NON_CANCELABLE
  43
  44 extern "C" {
  45
  46 #if !__DARWIN_ONLY_UNIX_CONFORMANCE
  47
  48 // When there's a choice between UNIX2003 and pre-UNIX2003. There's no
  49 // close$NOCANCEL symbol in this case, so use close$NOCANCEL$UNIX2003 as the
  50 // implementation. It does the same thing that close$NOCANCEL would do.
  51 #define close_implementation close$NOCANCEL$UNIX2003
  52
  53 #else  // __DARWIN_ONLY_UNIX_CONFORMANCE
  54
  55 // When only UNIX2003 is supported:
  56 #define close_implementation close$NOCANCEL
  57
  58 #endif
  59
  60 int close_implementation(int fd);
  61
  62 int close(int fd) {
  63   return close_implementation(fd);
  64 }
  65
  66 #undef close_implementation
  67
  68 }  // extern "C"
  69
  70 #endif  // !__DARWIN_NON_CANCELABLE