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 function calls the 32// $NOCANCEL variant, which is resolved from libsyscall. By linking with this 33// version of close prior to the libsyscall version, close's implementation is 34// overridden. 35 36#include <sys/cdefs.h> 37 38// If the non-cancelable variants of all system calls have already been 39// chosen, do nothing. 40#if !__DARWIN_NON_CANCELABLE 41 42extern "C" { 43 44#if __DARWIN_UNIX03 && !__DARWIN_ONLY_UNIX_CONFORMANCE 45 46// When there's a choice between UNIX2003 and pre-UNIX2003 and UNIX2003 has 47// been chosen: 48#define close_interface close$UNIX2003 49#define close_implementation close$NOCANCEL$UNIX2003 50 51#elif !__DARWIN_UNIX03 && !__DARWIN_ONLY_UNIX_CONFORMANCE 52 53// When there's a choice between UNIX2003 and pre-UNIX2003 and pre-UNIX2003 54// has been chosen. There's no close$NOCANCEL symbol in this case, so use 55// close$NOCANCEL$UNIX2003 as the implementation. It does the same thing 56// that close$NOCANCEL would do. 57#define close_interface close 58#define close_implementation close$NOCANCEL$UNIX2003 59 60#else // __DARWIN_ONLY_UNIX_CONFORMANCE 61 62// When only UNIX2003 is supported: 63#define close_interface close 64#define close_implementation close$NOCANCEL 65 66#endif 67 68int close_implementation(int fd); 69 70int close_interface(int fd) { 71 return close_implementation(fd); 72} 73 74#undef close_interface 75#undef close_implementation 76 77} // extern "C" 78 79#endif // !__DARWIN_NON_CANCELABLE 80