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glibc/sysdeps/nptl/libc-lockP.h
Adhemerval Zanella 27761a1042 Refactor atfork handlers 
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.
2018-02-22 16:43:59 -03:00

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/* Private libc-internal interface for mutex locks. NPTL version.
Copyright (C) 1996-2018 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation; either version 2.1 of the
License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; see the file COPYING.LIB. If
not, see <http://www.gnu.org/licenses/>. */
#ifndef _LIBC_LOCKP_H
#define _LIBC_LOCKP_H 1
#include <pthread.h>
#define __need_NULL
#include <stddef.h>
/* Fortunately Linux now has a mean to do locking which is realtime
safe without the aid of the thread library. We also need no fancy
options like error checking mutexes etc. We only need simple
locks, maybe recursive. This can be easily and cheaply implemented
using futexes. We will use them everywhere except in ld.so since
ld.so might be used on old kernels with a different libc.so. */
#include <lowlevellock.h>
#include <tls.h>
#include <pthread-functions.h>
#if IS_IN (libpthread)
/* This gets us the declarations of the __pthread_* internal names,
and hidden_proto for them. */
# include <nptl/pthreadP.h>
#endif
/* Mutex type. */
#if !IS_IN (libc) && !IS_IN (libpthread)
typedef pthread_mutex_t __libc_lock_t;
#else
typedef int __libc_lock_t;
#endif
typedef struct { pthread_mutex_t mutex; } __rtld_lock_recursive_t;
typedef pthread_rwlock_t __libc_rwlock_t;
/* Type for key to thread-specific data. */
typedef pthread_key_t __libc_key_t;
/* Define a lock variable NAME with storage class CLASS. The lock must be
initialized with __libc_lock_init before it can be used (or define it
with __libc_lock_define_initialized, below). Use `extern' for CLASS to
declare a lock defined in another module. In public structure
definitions you must use a pointer to the lock structure (i.e., NAME
begins with a `*'), because its storage size will not be known outside
of libc. */
#define __libc_lock_define(CLASS,NAME) \
CLASS __libc_lock_t NAME;
#define __libc_rwlock_define(CLASS,NAME) \
CLASS __libc_rwlock_t NAME;
#define __rtld_lock_define_recursive(CLASS,NAME) \
CLASS __rtld_lock_recursive_t NAME;
/* Define an initialized lock variable NAME with storage class CLASS.
For the C library we take a deeper look at the initializer. For
this implementation all fields are initialized to zero. Therefore
we don't initialize the variable which allows putting it into the
BSS section. (Except on PA-RISC and other odd architectures, where
initialized locks must be set to one due to the lack of normal
atomic operations.) */
#define _LIBC_LOCK_INITIALIZER LLL_LOCK_INITIALIZER
#if IS_IN (libc) || IS_IN (libpthread)
# if LLL_LOCK_INITIALIZER == 0
# define __libc_lock_define_initialized(CLASS,NAME) \
CLASS __libc_lock_t NAME;
# else
# define __libc_lock_define_initialized(CLASS,NAME) \
CLASS __libc_lock_t NAME = LLL_LOCK_INITIALIZER;
# endif
#else
# define __libc_lock_define_initialized(CLASS,NAME) \
CLASS __libc_lock_t NAME;
#endif
#define __libc_rwlock_define_initialized(CLASS,NAME) \
CLASS __libc_rwlock_t NAME = PTHREAD_RWLOCK_INITIALIZER;
#define __rtld_lock_define_initialized_recursive(CLASS,NAME) \
CLASS __rtld_lock_recursive_t NAME = _RTLD_LOCK_RECURSIVE_INITIALIZER;
#define _RTLD_LOCK_RECURSIVE_INITIALIZER \
{PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP}
#define __rtld_lock_initialize(NAME) \
(void) ((NAME) = (__rtld_lock_recursive_t) _RTLD_LOCK_RECURSIVE_INITIALIZER)
/* If we check for a weakly referenced symbol and then perform a
normal jump to it te code generated for some platforms in case of
PIC is unnecessarily slow. What would happen is that the function
is first referenced as data and then it is called indirectly
through the PLT. We can make this a direct jump. */
#ifdef __PIC__
# define __libc_maybe_call(FUNC, ARGS, ELSE) \
(__extension__ ({ __typeof (FUNC) *_fn = (FUNC); \
_fn != NULL ? (*_fn) ARGS : ELSE; }))
#else
# define __libc_maybe_call(FUNC, ARGS, ELSE) \
(FUNC != NULL ? FUNC ARGS : ELSE)
#endif
/* Call thread functions through the function pointer table. */
#if defined SHARED && IS_IN (libc)
# define PTFAVAIL(NAME) __libc_pthread_functions_init
# define __libc_ptf_call(FUNC, ARGS, ELSE) \
(__libc_pthread_functions_init ? PTHFCT_CALL (ptr_##FUNC, ARGS) : ELSE)
# define __libc_ptf_call_always(FUNC, ARGS) \
PTHFCT_CALL (ptr_##FUNC, ARGS)
#elif IS_IN (libpthread)
# define PTFAVAIL(NAME) 1
# define __libc_ptf_call(FUNC, ARGS, ELSE) \
FUNC ARGS
# define __libc_ptf_call_always(FUNC, ARGS) \
FUNC ARGS
#else
# define PTFAVAIL(NAME) (NAME != NULL)
# define __libc_ptf_call(FUNC, ARGS, ELSE) \
__libc_maybe_call (FUNC, ARGS, ELSE)
# define __libc_ptf_call_always(FUNC, ARGS) \
FUNC ARGS
#endif
/* Initialize the named lock variable, leaving it in a consistent, unlocked
state. */
#if IS_IN (libc) || IS_IN (libpthread)
# define __libc_lock_init(NAME) \
((void) ((NAME) = LLL_LOCK_INITIALIZER))
#else
# define __libc_lock_init(NAME) \
__libc_maybe_call (__pthread_mutex_init, (&(NAME), NULL), 0)
#endif
#if defined SHARED && IS_IN (libc)
/* ((NAME) = (__libc_rwlock_t) PTHREAD_RWLOCK_INITIALIZER) is inefficient. */
# define __libc_rwlock_init(NAME) \
((void) __builtin_memset (&(NAME), '\0', sizeof (NAME)))
#else
# define __libc_rwlock_init(NAME) \
__libc_maybe_call (__pthread_rwlock_init, (&(NAME), NULL), 0)
#endif
/* Finalize the named lock variable, which must be locked. It cannot be
used again until __libc_lock_init is called again on it. This must be
called on a lock variable before the containing storage is reused. */
#if IS_IN (libc) || IS_IN (libpthread)
# define __libc_lock_fini(NAME) ((void) 0)
#else
# define __libc_lock_fini(NAME) \
__libc_maybe_call (__pthread_mutex_destroy, (&(NAME)), 0)
#endif
#if defined SHARED && IS_IN (libc)
# define __libc_rwlock_fini(NAME) ((void) 0)
#else
# define __libc_rwlock_fini(NAME) \
__libc_maybe_call (__pthread_rwlock_destroy, (&(NAME)), 0)
#endif
/* Lock the named lock variable. */
#if IS_IN (libc) || IS_IN (libpthread)
# ifndef __libc_lock_lock
# define __libc_lock_lock(NAME) \
({ lll_lock (NAME, LLL_PRIVATE); 0; })
# endif
#else
# undef __libc_lock_lock
# define __libc_lock_lock(NAME) \
__libc_maybe_call (__pthread_mutex_lock, (&(NAME)), 0)
#endif
#define __libc_rwlock_rdlock(NAME) \
__libc_ptf_call (__pthread_rwlock_rdlock, (&(NAME)), 0)
#define __libc_rwlock_wrlock(NAME) \
__libc_ptf_call (__pthread_rwlock_wrlock, (&(NAME)), 0)
/* Try to lock the named lock variable. */
#if IS_IN (libc) || IS_IN (libpthread)
# ifndef __libc_lock_trylock
# define __libc_lock_trylock(NAME) \
lll_trylock (NAME)
# endif
#else
# undef __libc_lock_trylock
# define __libc_lock_trylock(NAME) \
__libc_maybe_call (__pthread_mutex_trylock, (&(NAME)), 0)
#endif
#define __libc_rwlock_tryrdlock(NAME) \
__libc_maybe_call (__pthread_rwlock_tryrdlock, (&(NAME)), 0)
#define __libc_rwlock_trywrlock(NAME) \
__libc_maybe_call (__pthread_rwlock_trywrlock, (&(NAME)), 0)
#define __rtld_lock_trylock_recursive(NAME) \
__libc_maybe_call (__pthread_mutex_trylock, (&(NAME).mutex), 0)
/* Unlock the named lock variable. */
#if IS_IN (libc) || IS_IN (libpthread)
# define __libc_lock_unlock(NAME) \
lll_unlock (NAME, LLL_PRIVATE)
#else
# define __libc_lock_unlock(NAME) \
__libc_maybe_call (__pthread_mutex_unlock, (&(NAME)), 0)
#endif
#define __libc_rwlock_unlock(NAME) \
__libc_ptf_call (__pthread_rwlock_unlock, (&(NAME)), 0)
#ifdef SHARED
# define __rtld_lock_default_lock_recursive(lock) \
++((pthread_mutex_t *)(lock))->__data.__count;
# define __rtld_lock_default_unlock_recursive(lock) \
--((pthread_mutex_t *)(lock))->__data.__count;
# define __rtld_lock_lock_recursive(NAME) \
GL(dl_rtld_lock_recursive) (&(NAME).mutex)
# define __rtld_lock_unlock_recursive(NAME) \
GL(dl_rtld_unlock_recursive) (&(NAME).mutex)
#else
# define __rtld_lock_lock_recursive(NAME) \
__libc_maybe_call (__pthread_mutex_lock, (&(NAME).mutex), 0)
# define __rtld_lock_unlock_recursive(NAME) \
__libc_maybe_call (__pthread_mutex_unlock, (&(NAME).mutex), 0)
#endif
/* Define once control variable. */
#if PTHREAD_ONCE_INIT == 0
/* Special case for static variables where we can avoid the initialization
if it is zero. */
# define __libc_once_define(CLASS, NAME) \
CLASS pthread_once_t NAME
#else
# define __libc_once_define(CLASS, NAME) \
CLASS pthread_once_t NAME = PTHREAD_ONCE_INIT
#endif
/* Call handler iff the first call. */
#define __libc_once(ONCE_CONTROL, INIT_FUNCTION) \
do { \
if (PTFAVAIL (__pthread_once)) \
__libc_ptf_call_always (__pthread_once, (&(ONCE_CONTROL), \
INIT_FUNCTION)); \
else if ((ONCE_CONTROL) == PTHREAD_ONCE_INIT) { \
INIT_FUNCTION (); \
(ONCE_CONTROL) |= 2; \
} \
} while (0)
/* Get once control variable. */
#define __libc_once_get(ONCE_CONTROL) ((ONCE_CONTROL) != PTHREAD_ONCE_INIT)
/* Note that for I/O cleanup handling we are using the old-style
cancel handling. It does not have to be integrated with C++ snce
no C++ code is called in the middle. The old-style handling is
faster and the support is not going away. */
extern void _pthread_cleanup_push (struct _pthread_cleanup_buffer *buffer,
void (*routine) (void *), void *arg);
extern void _pthread_cleanup_pop (struct _pthread_cleanup_buffer *buffer,
int execute);
extern void _pthread_cleanup_push_defer (struct _pthread_cleanup_buffer *buffer,
void (*routine) (void *), void *arg);
extern void _pthread_cleanup_pop_restore (struct _pthread_cleanup_buffer *buffer,
int execute);
/* Sometimes we have to exit the block in the middle. */
#define __libc_cleanup_end(DOIT) \
if (_avail) { \
__libc_ptf_call_always (_pthread_cleanup_pop_restore, (&_buffer, DOIT));\
} else if (DOIT) \
_buffer.__routine (_buffer.__arg)
/* Normal cleanup handling, based on C cleanup attribute. */
__extern_inline void
__libc_cleanup_routine (struct __pthread_cleanup_frame *f)
{
if (f->__do_it)
f->__cancel_routine (f->__cancel_arg);
}
#define __libc_cleanup_push(fct, arg) \
do { \
struct __pthread_cleanup_frame __clframe \
__attribute__ ((__cleanup__ (__libc_cleanup_routine))) \
= { .__cancel_routine = (fct), .__cancel_arg = (arg), \
.__do_it = 1 };
#define __libc_cleanup_pop(execute) \
__clframe.__do_it = (execute); \
} while (0)
/* Create thread-specific key. */
#define __libc_key_create(KEY, DESTRUCTOR) \
__libc_ptf_call (__pthread_key_create, (KEY, DESTRUCTOR), 1)
/* Get thread-specific data. */
#define __libc_getspecific(KEY) \
__libc_ptf_call (__pthread_getspecific, (KEY), NULL)
/* Set thread-specific data. */
#define __libc_setspecific(KEY, VALUE) \
__libc_ptf_call (__pthread_setspecific, (KEY, VALUE), 0)
/* Register handlers to execute before and after `fork'. Note that the
last parameter is NULL. The handlers registered by the libc are
never removed so this is OK. */
extern int __register_atfork (void (*__prepare) (void),
void (*__parent) (void),
void (*__child) (void),
void *__dso_handle);
/* Functions that are used by this file and are internal to the GNU C
library. */
extern int __pthread_mutex_init (pthread_mutex_t *__mutex,
const pthread_mutexattr_t *__mutex_attr);
extern int __pthread_mutex_destroy (pthread_mutex_t *__mutex);
extern int __pthread_mutex_trylock (pthread_mutex_t *__mutex);
extern int __pthread_mutex_lock (pthread_mutex_t *__mutex);
extern int __pthread_mutex_unlock (pthread_mutex_t *__mutex);
extern int __pthread_mutexattr_init (pthread_mutexattr_t *__attr);
extern int __pthread_mutexattr_destroy (pthread_mutexattr_t *__attr);
extern int __pthread_mutexattr_settype (pthread_mutexattr_t *__attr,
int __kind);
extern int __pthread_rwlock_init (pthread_rwlock_t *__rwlock,
const pthread_rwlockattr_t *__attr);
extern int __pthread_rwlock_destroy (pthread_rwlock_t *__rwlock);
extern int __pthread_rwlock_rdlock (pthread_rwlock_t *__rwlock);
extern int __pthread_rwlock_tryrdlock (pthread_rwlock_t *__rwlock);
extern int __pthread_rwlock_wrlock (pthread_rwlock_t *__rwlock);
extern int __pthread_rwlock_trywrlock (pthread_rwlock_t *__rwlock);
extern int __pthread_rwlock_unlock (pthread_rwlock_t *__rwlock);
extern int __pthread_key_create (pthread_key_t *__key,
void (*__destr_function) (void *));
extern int __pthread_setspecific (pthread_key_t __key,
const void *__pointer);
extern void *__pthread_getspecific (pthread_key_t __key);
extern int __pthread_once (pthread_once_t *__once_control,
void (*__init_routine) (void));
extern int __pthread_atfork (void (*__prepare) (void),
void (*__parent) (void),
void (*__child) (void));
extern int __pthread_setcancelstate (int state, int *oldstate);
/* Make the pthread functions weak so that we can elide them from
single-threaded processes. */
#ifndef __NO_WEAK_PTHREAD_ALIASES
# ifdef weak_extern
weak_extern (__pthread_mutex_init)
weak_extern (__pthread_mutex_destroy)
weak_extern (__pthread_mutex_lock)
weak_extern (__pthread_mutex_trylock)
weak_extern (__pthread_mutex_unlock)
weak_extern (__pthread_mutexattr_init)
weak_extern (__pthread_mutexattr_destroy)
weak_extern (__pthread_mutexattr_settype)
weak_extern (__pthread_rwlock_init)
weak_extern (__pthread_rwlock_destroy)
weak_extern (__pthread_rwlock_rdlock)
weak_extern (__pthread_rwlock_tryrdlock)
weak_extern (__pthread_rwlock_wrlock)
weak_extern (__pthread_rwlock_trywrlock)
weak_extern (__pthread_rwlock_unlock)
weak_extern (__pthread_key_create)
weak_extern (__pthread_setspecific)
weak_extern (__pthread_getspecific)
weak_extern (__pthread_once)
weak_extern (__pthread_initialize)
weak_extern (__pthread_atfork)
weak_extern (__pthread_setcancelstate)
weak_extern (_pthread_cleanup_push_defer)
weak_extern (_pthread_cleanup_pop_restore)
# else
# pragma weak __pthread_mutex_init
# pragma weak __pthread_mutex_destroy
# pragma weak __pthread_mutex_lock
# pragma weak __pthread_mutex_trylock
# pragma weak __pthread_mutex_unlock
# pragma weak __pthread_mutexattr_init
# pragma weak __pthread_mutexattr_destroy
# pragma weak __pthread_mutexattr_settype
# pragma weak __pthread_rwlock_destroy
# pragma weak __pthread_rwlock_rdlock
# pragma weak __pthread_rwlock_tryrdlock
# pragma weak __pthread_rwlock_wrlock
# pragma weak __pthread_rwlock_trywrlock
# pragma weak __pthread_rwlock_unlock
# pragma weak __pthread_key_create
# pragma weak __pthread_setspecific
# pragma weak __pthread_getspecific
# pragma weak __pthread_once
# pragma weak __pthread_initialize
# pragma weak __pthread_atfork
# pragma weak __pthread_setcancelstate
# pragma weak _pthread_cleanup_push_defer
# pragma weak _pthread_cleanup_pop_restore
# endif
#endif
#endif /* libc-lockP.h */
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