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qbatomic.h
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/*
* Copyright (C) 2003 Sebastian Wilhelmi
*
* This file is part of libqb.
*
* libqb 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.
*
* libqb 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 libqb. If not, see <http://www.gnu.org/licenses/>.
*/
/*
* Copied from the glib code base (glib/gatomic.h) and namespaced
* for libqb.
*/
#ifndef QB_ATOMIC_DEFINED
#define QB_ATOMIC_DEFINED
#include <stdint.h>
#include <qb/qbdefs.h>
/**
* @file
* Basic atomic integer and pointer operations
*
* The following functions can be used to atomically access integers and
* pointers. They are implemented as inline assembler function on most
* platforms and use slower fall-backs otherwise. Using them can sometimes
* save you from using a performance-expensive pthread_mutex to protect the
* integer or pointer.
*
* The most important usage is reference counting. Using
* qb_atomic_int_inc() and qb_atomic_int_dec_and_test() makes reference
* counting a very fast operation.
*
* You must not directly read integers or pointers concurrently
* accessed by multiple threads, but use the atomic accessor functions
* instead. That is, always use qb_atomic_int_get() and qb_atomic_pointer_get()
* for read outs. They provide the neccessary synchonization mechanisms
* like memory barriers to access memory locations concurrently.
*
* If you are using those functions for anything apart from
* simple reference counting, you should really be aware of the implications
* of doing that. There are literally thousands of ways to shoot yourself
* in the foot. So if in doubt, use a pthread_mutex. If you don't know, what
* memory barriers are, do not use anything but qb_atomic_int_inc() and
* qb_atomic_int_dec_and_test().
*
* It is not safe to set an integer or pointer just by assigning
* to it, when it is concurrently accessed by other threads with the following
* functions. Use qb_atomic_int_compare_and_exchange() or
* qb_atomic_pointer_compare_and_exchange() respectively.
*/
/* *INDENT-OFF* */
#ifdef __cplusplus
extern "C" {
#endif
/* *INDENT-ON* */
void qb_atomic_init(void);
/**
* Atomically adds val to the integer pointed to by atomic.
* It returns the value of *atomic just before the addition
* took place. Also acts as a memory barrier.
*
* @param atomic a pointer to an integer
* @param val the value to add to *atomic
* @return the value of *atomic before the addition.
*/
int32_t qb_atomic_int_exchange_and_add(volatile int32_t QB_GNUC_MAY_ALIAS *
atomic, int32_t val);
/**
* Atomically adds val to the integer pointed to by atomic.
* Also acts as a memory barrier.
*
* @param atomic a pointer to an integer
* @param val the value to add to *atomic
*/
void qb_atomic_int_add(volatile int32_t QB_GNUC_MAY_ALIAS * atomic, int32_t val);
/**
* Compares oldval with the integer pointed to by atomic and
* if they are equal, atomically exchanges *atomic with newval.
* Also acts as a memory barrier.
*
* @param atomic a pointer to an integer
* @param oldval the assumed old value of *atomic
* @param newval the new value of *atomic
*
* @return QB_TRUE, if *atomic was equal oldval. QB_FALSE otherwise.
*/
int32_t qb_atomic_int_compare_and_exchange(volatile int32_t QB_GNUC_MAY_ALIAS *
atomic, int32_t oldval,
int32_t newval);
/**
* Compares oldval with the pointer pointed to by atomic and
* if they are equal, atomically exchanges *atomic with newval.
* Also acts as a memory barrier.
*
* @param atomic a pointer to a void*
* @param oldval the assumed old value of *atomic
* @param newval the new value of *atomic
*
* @return QB_TRUE if atomic was equal oldval, else QB_FALSE.
*/
int32_t qb_atomic_pointer_compare_and_exchange(volatile void* QB_GNUC_MAY_ALIAS
* atomic, void* oldval,
void* newval);
/**
* Reads the value of the integer pointed to by atomic.
* Also acts as a memory barrier.
*
* @param atomic a pointer to an integer
*
* @return the value of atomic
*/
int32_t qb_atomic_int_get(volatile int32_t QB_GNUC_MAY_ALIAS * atomic);
/**
* Sets the value of the integer pointed to by atomic.
* Also acts as a memory barrier.
*
* @param atomic a pointer to an integer
* @param newval the new value
*/
void qb_atomic_int_set(volatile int32_t QB_GNUC_MAY_ALIAS * atomic,
int32_t newval);
/**
* Reads the value of the pointer pointed to by atomic.
* Also acts as a memory barrier.
*
* @param atomic a pointer to a void*.
* @return the value to add to atomic.
*/
void* qb_atomic_pointer_get(volatile void* QB_GNUC_MAY_ALIAS * atomic);
/**
* Sets the value of the pointer pointed to by atomic.
* Also acts as a memory barrier.
*
* @param atomic a pointer to a void*
* @param newval the new value
*
*/
void qb_atomic_pointer_set(volatile void* QB_GNUC_MAY_ALIAS * atomic,
void* newval);
#ifndef QB_ATOMIC_OP_MEMORY_BARRIER_NEEDED
#define qb_atomic_int_get(atomic) ((int32_t)*(atomic))
#define qb_atomic_int_set(atomic, newval) ((void) (*(atomic) = (newval)))
#define qb_atomic_pointer_get(atomic) ((void*)*(atomic))
#define qb_atomic_pointer_set(atomic, newval) ((void) (*(atomic) = (newval)))
#else
#define qb_atomic_int_get(atomic) \
((void) sizeof (char* [sizeof (*(atomic)) == sizeof (int32_t) ? 1 : -1]), \
(qb_atomic_int_get) ((volatile int32_t QB_GNUC_MAY_ALIAS *) (volatile void *) (atomic)))
#define qb_atomic_int_set(atomic, newval) \
((void) sizeof (char* [sizeof (*(atomic)) == sizeof (int32_t) ? 1 : -1]), \
(qb_atomic_int_set) ((volatile int32_t QB_GNUC_MAY_ALIAS *) (volatile void *) (atomic), (newval)))
#define qb_atomic_pointer_get(atomic) \
((void) sizeof (char* [sizeof (*(atomic)) == sizeof (void*) ? 1 : -1]), \
(qb_atomic_pointer_get) ((volatile void QB_GNUC_MAY_ALIAS *) (volatile void *) (atomic)))
#define qb_atomic_pointer_set(atomic, newval) \
((void) sizeof (char* [sizeof (*(atomic)) == sizeof (void*) ? 1 : -1]), \
(qb_atomic_pointer_set) ((volatile void QB_GNUC_MAY_ALIAS *) (volatile void *) (atomic), (newval)))
#endif /* QB_ATOMIC_OP_MEMORY_BARRIER_NEEDED */
/**
* Atomically increments the integer pointed to by atomic by 1.
*
* @param atomic a pointer to an integer.
*/
#define qb_atomic_int_inc(atomic) (qb_atomic_int_add ((atomic), 1))
/**
* Atomically decrements the integer pointed to by atomic by 1.
*
* @param atomic a pointer to an integer
*
* @return QB_TRUE if the integer pointed to by atomic is 0
* after decrementing it
*/
#define qb_atomic_int_dec_and_test(atomic) \
(qb_atomic_int_exchange_and_add ((atomic), -1) == 1)
/* *INDENT-OFF* */
#ifdef __cplusplus
}
#endif
/* *INDENT-ON* */
#endif /* QB_ATOMIC_DEFINED */
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