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