27761a1042
Current implementation (sysdeps/nptl/fork.c) replicates the atfork handlers list backward to invoke the child handlers after fork/clone syscall. The internal atfork handlers is implemented as a single-linked list so a lock-free algorithm can be used, trading fork mulithread call performance for some code complexity and dynamic stack allocation (since the backwards list should not fail). This patch refactor it to use a dynarary instead of a linked list. It simplifies the external variables need to be exported and also the internal atfork handler member definition. The downside is a serialization of fork call in multithread, since to operate on the dynarray the internal lock should be used. However as noted by Florian, it already acquires external locks for malloc and libio so it is already hitting some lock contention. Besides, posix_spawn should be faster and more scalable to run external programs in multithread environments. Checked on x86_64-linux-gnu. * nptl/Makefile (routines): Remove unregister-atfork. * nptl/register-atfork.c (fork_handler_pool): Remove variable. (fork_handler_alloc): Remove function. (fork_handlers, fork_handler_init): New variables. (__fork_lock): Rename to atfork_lock. (__register_atfork, __unregister_atfork, libc_freeres_fn): Rewrite to use a dynamic array to add/remove atfork handlers. * sysdeps/nptl/fork.c (__libc_fork): Likewise. * sysdeps/nptl/fork.h (__fork_lock, __fork_handlers, __linkin_atfork): Remove declaration. (fork_handler): Remove next, refcntr, and need_signal member. (__run_fork_handler_type): New enum. (__run_fork_handlers): New prototype. * sysdeps/nptl/libc-lockP.h (__libc_atfork): Remove declaration.
65 lines
2.3 KiB
C
65 lines
2.3 KiB
C
/* Copyright (C) 2002-2018 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 <lowlevellock.h>
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/* The fork generation counter, defined in libpthread. */
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extern unsigned long int __fork_generation attribute_hidden;
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/* Pointer to the fork generation counter in the thread library. */
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extern unsigned long int *__fork_generation_pointer attribute_hidden;
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/* Elements of the fork handler lists. */
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struct fork_handler
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{
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void (*prepare_handler) (void);
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void (*parent_handler) (void);
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void (*child_handler) (void);
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void *dso_handle;
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};
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/* Function to call to unregister fork handlers. */
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extern void __unregister_atfork (void *dso_handle) attribute_hidden;
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#define UNREGISTER_ATFORK(dso_handle) __unregister_atfork (dso_handle)
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enum __run_fork_handler_type
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{
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atfork_run_prepare,
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atfork_run_child,
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atfork_run_parent
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};
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/* Run the atfork handlers and lock/unlock the internal lock depending
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of the WHO argument:
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- atfork_run_prepare: run all the PREPARE_HANDLER in reverse order of
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insertion and locks the internal lock.
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- atfork_run_child: run all the CHILD_HANDLER and unlocks the internal
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lock.
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- atfork_run_parent: run all the PARENT_HANDLER and unlocks the internal
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lock. */
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extern void __run_fork_handlers (enum __run_fork_handler_type who)
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attribute_hidden;
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/* C library side function to register new fork handlers. */
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extern int __register_atfork (void (*__prepare) (void),
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void (*__parent) (void),
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void (*__child) (void),
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void *dso_handle);
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libc_hidden_proto (__register_atfork)
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