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a2f0363f81
This adds new functions for futex operations, starting with wait, abstimed_wait, reltimed_wait, wake. They add documentation and error checking according to the current draft of the Linux kernel futex manpage. Waiting with absolute or relative timeouts is split into separate functions. This allows for removing a few cases of code duplication in pthreads code, which uses absolute timeouts; also, it allows us to put platform-specific code to go from an absolute to a relative timeout into the platform-specific futex abstractions.. Futex operations that can be canceled are also split out into separate functions suffixed by "_cancelable". There are separate versions for both Linux and NaCl; while they currently differ only slightly, my expectation is that the separate versions of lowlevellock-futex.h will eventually be merged into futex-internal.h when we get to move the lll_ functions over to the new futex API.
123 lines
3.6 KiB
C
123 lines
3.6 KiB
C
/* Copyright (C) 2002-2015 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <errno.h>
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#include <stdlib.h>
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#include <fork.h>
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#include <atomic.h>
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#include <futex-internal.h>
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void
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__unregister_atfork (dso_handle)
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void *dso_handle;
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{
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/* Check whether there is any entry in the list which we have to
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remove. It is likely that this is not the case so don't bother
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getting the lock.
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We do not worry about other threads adding entries for this DSO
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right this moment. If this happens this is a race and we can do
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whatever we please. The program will crash anyway seen. */
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struct fork_handler *runp = __fork_handlers;
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struct fork_handler *lastp = NULL;
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while (runp != NULL)
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if (runp->dso_handle == dso_handle)
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break;
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else
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{
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lastp = runp;
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runp = runp->next;
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}
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if (runp == NULL)
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/* Nothing to do. */
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return;
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/* Get the lock to not conflict with additions or deletions. Note
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that there couldn't have been another thread deleting something.
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The __unregister_atfork function is only called from the
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dlclose() code which itself serializes the operations. */
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lll_lock (__fork_lock, LLL_PRIVATE);
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/* We have to create a new list with all the entries we don't remove. */
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struct deleted_handler
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{
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struct fork_handler *handler;
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struct deleted_handler *next;
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} *deleted = NULL;
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/* Remove the entries for the DSO which is unloaded from the list.
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It's a single linked list so readers are. */
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do
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{
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again:
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if (runp->dso_handle == dso_handle)
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{
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if (lastp == NULL)
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{
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/* We have to use an atomic operation here because
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__linkin_atfork also uses one. */
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if (catomic_compare_and_exchange_bool_acq (&__fork_handlers,
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runp->next, runp)
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!= 0)
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{
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runp = __fork_handlers;
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goto again;
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}
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}
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else
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lastp->next = runp->next;
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/* We cannot overwrite the ->next element now. Put the deleted
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entries in a separate list. */
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struct deleted_handler *newp = alloca (sizeof (*newp));
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newp->handler = runp;
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newp->next = deleted;
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deleted = newp;
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}
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else
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lastp = runp;
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runp = runp->next;
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}
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while (runp != NULL);
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/* Release the lock. */
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lll_unlock (__fork_lock, LLL_PRIVATE);
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/* Walk the list of all entries which have to be deleted. */
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while (deleted != NULL)
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{
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/* We need to be informed by possible current users. */
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deleted->handler->need_signal = 1;
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/* Make sure this gets written out first. */
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atomic_write_barrier ();
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/* Decrement the reference counter. If it does not reach zero
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wait for the last user. */
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atomic_decrement (&deleted->handler->refcntr);
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unsigned int val;
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while ((val = deleted->handler->refcntr) != 0)
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futex_wait_simple (&deleted->handler->refcntr, val, FUTEX_PRIVATE);
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deleted = deleted->next;
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}
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}
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