apr_atomic.h

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/* Copyright 2000-2005 The Apache Software Foundation or its licensors, as
 * applicable.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef APR_ATOMIC_H
#define APR_ATOMIC_H

/**
 * @file apr_atomic.h
 * @brief APR Atomic Operations
 */

#include "apr.h"
#include "apr_pools.h"

/* Platform includes for atomics */
#if defined(NETWARE) || defined(__MVS__) /* OS/390 */
#include <stdlib.h>
#elif defined(__FreeBSD__)
#include <machine/atomic.h>
#endif

#ifdef __cplusplus
extern "C" {
#endif

/**
 * @defgroup apr_atomic Atomic Operations
 * @ingroup APR 
 * @{
 */

/* easiest way to get these documented for the moment */
#if defined(DOXYGEN)
/**
 * structure for holding a atomic value.
 * this number >only< has a 24 bit size on some platforms
 */
typedef apr_atomic_t;

/**
 * this function is required on some platforms to initialize the
 * atomic operation's internal structures
 * @param p pool
 * @return APR_SUCCESS on successful completion
 */
apr_status_t apr_atomic_init(apr_pool_t *p);
/**
 * read the value stored in a atomic variable
 * @param mem the pointer
 * @warning on certain platforms this number is not stored
 * directly in the pointer. in others it is 
 */
apr_uint32_t apr_atomic_read(volatile apr_atomic_t *mem);
/**
 * set the value for atomic.
 * @param mem the pointer
 * @param val the value
 */
void apr_atomic_set(volatile apr_atomic_t *mem, apr_uint32_t val);
/**
 * Add 'val' to the atomic variable
 * @param mem pointer to the atomic value
 * @param val the addition
 */
void apr_atomic_add(volatile apr_atomic_t *mem, apr_uint32_t val);

/**
 * increment the atomic variable by 1
 * @param mem pointer to the atomic value
 */
void apr_atomic_inc(volatile apr_atomic_t *mem);

/**
 * decrement the atomic variable by 1
 * @param mem pointer to the atomic value
 * @return zero if the value is zero, otherwise non-zero
 */
int apr_atomic_dec(volatile apr_atomic_t *mem);

/**
 * compare the atomic's value with cmp.
 * If they are the same swap the value with 'with'
 * @param mem pointer to the atomic value
 * @param with what to swap it with
 * @param cmp the value to compare it to
 * @return the old value of the atomic
 * @warning do not mix apr_atomic's with the CAS function.
 * on some platforms they may be implemented by different mechanisms
 */
apr_uint32_t apr_atomic_cas(volatile apr_uint32_t *mem, long with, long cmp);

/**
 * compare the pointer's value with cmp.
 * If they are the same swap the value with 'with'
 * @param mem pointer to the pointer
 * @param with what to swap it with
 * @param cmp the value to compare it to
 * @return the old value of the pointer
 */
void *apr_atomic_casptr(volatile void **mem, void *with, const void *cmp);
#else /* !DOXYGEN */

/* The following definitions provide optimized, OS-specific
 * implementations of the APR atomic functions on various
 * platforms.  Any atomic operation that isn't redefined as
 * a macro here will be declared as a function later, and
 * apr_atomic.c will provide a mutex-based default implementation.
 */

#if defined(WIN32)

#define apr_atomic_t LONG

#define apr_atomic_add(mem, val)     InterlockedExchangeAdd(mem,val)
#define apr_atomic_dec(mem)          InterlockedDecrement(mem)
#define apr_atomic_inc(mem)          InterlockedIncrement(mem)
#define apr_atomic_set(mem, val)     InterlockedExchange(mem, val)
#define apr_atomic_read(mem)         (*mem)
#define apr_atomic_cas(mem,with,cmp) InterlockedCompareExchange(mem,with,cmp)
#define apr_atomic_init(pool)        APR_SUCCESS
#define apr_atomic_casptr(mem,with,cmp) InterlockedCompareExchangePointer(mem,with,cmp)

#elif defined(NETWARE)

#define apr_atomic_t unsigned long

#define apr_atomic_add(mem, val)     atomic_add(mem,val)
#define apr_atomic_inc(mem)          atomic_inc(mem)
#define apr_atomic_set(mem, val)     (*mem = val)
#define apr_atomic_read(mem)         (*mem)
#define apr_atomic_init(pool)        APR_SUCCESS
#define apr_atomic_cas(mem,with,cmp) atomic_cmpxchg((unsigned long *)(mem),(unsigned long)(cmp),(unsigned long)(with))
    
int apr_atomic_dec(apr_atomic_t *mem);
void *apr_atomic_casptr(void **mem, void *with, const void *cmp);
#define APR_OVERRIDE_ATOMIC_DEC 1
#define APR_OVERRIDE_ATOMIC_CASPTR 1

inline int apr_atomic_dec(apr_atomic_t *mem) 
{
    return (atomic_xchgadd(mem, 0xFFFFFFFF) - 1);
}

inline void *apr_atomic_casptr(void **mem, void *with, const void *cmp)
{
    return (void*)atomic_cmpxchg((unsigned long *)mem,(unsigned long)cmp,(unsigned long)with);
}

#elif defined(__FreeBSD__)

#define apr_atomic_t apr_uint32_t
#define apr_atomic_add(mem, val)     (atomic_add_int(mem,val),mem)
#define apr_atomic_dec(mem)          (atomic_subtract_int(mem,1),mem)
#define apr_atomic_inc(mem)          (atomic_add_int(mem,1),mem)
#define apr_atomic_set(mem, val)     (atomic_set_int(mem, val),mem)
#define apr_atomic_read(mem)         (*mem)

#elif (defined(__linux__) || defined(__EMX__)) && defined(__i386__) && !APR_FORCE_ATOMIC_GENERIC

#define apr_atomic_t apr_uint32_t
#define apr_atomic_cas(mem,with,cmp) \
({ apr_atomic_t prev; \
    asm volatile ("lock; cmpxchgl %1, %2"              \
         : "=a" (prev)               \
         : "r" (with), "m" (*(mem)), "0"(cmp) \
         : "memory"); \
    prev;})

#define apr_atomic_add(mem, val)                                \
({ register apr_atomic_t last;                                  \
   do {                                                         \
       last = *(mem);                                           \
   } while (apr_atomic_cas((mem), last + (val), last) != last); \
  })

#define apr_atomic_dec(mem)                                     \
({ register apr_atomic_t last;                                  \
   do {                                                         \
       last = *(mem);                                           \
   } while (apr_atomic_cas((mem), last - 1, last) != last);     \
  (--last != 0); })

#define apr_atomic_inc(mem)                                     \
({ register apr_atomic_t last;                                  \
   do {                                                         \
       last = *(mem);                                           \
   } while (apr_atomic_cas((mem), last + 1, last) != last);     \
  })

#define apr_atomic_set(mem, val)     (*(mem) = val)
#define apr_atomic_read(mem)        (*(mem))
#define apr_atomic_init(pool)        APR_SUCCESS

#elif defined(__MVS__) /* OS/390 */

#define apr_atomic_t cs_t

apr_int32_t apr_atomic_add(volatile apr_atomic_t *mem, apr_int32_t val);
apr_uint32_t apr_atomic_cas(volatile apr_atomic_t *mem, apr_uint32_t swap, 
                            apr_uint32_t cmp);
#define APR_OVERRIDE_ATOMIC_ADD 1
#define APR_OVERRIDE_ATOMIC_CAS 1

#define apr_atomic_inc(mem)          apr_atomic_add(mem, 1)
#define apr_atomic_dec(mem)          apr_atomic_add(mem, -1)
#define apr_atomic_init(pool)        APR_SUCCESS

/* warning: the following two operations, _read and _set, are atomic
 * if the memory variables are aligned (the usual case).  
 * 
 * If you try really hard and manage to mis-align them, they are not 
 * guaranteed to be atomic on S/390.  But then your program will blow up 
 * with SIGBUS on a sparc, or with a S0C6 abend if you use the mis-aligned 
 * variables with other apr_atomic_* operations on OS/390.
 */

#define apr_atomic_read(p)           (*p)
#define apr_atomic_set(mem, val)     (*mem = val)

#endif /* end big if-elseif switch for platform-specifics */


/* Default implementation of the atomic API
 * The definitions above may override some or all of the
 * atomic functions with optimized, platform-specific versions.
 * Any operation that hasn't been overridden as a macro above
 * is declared as a function here, unless APR_OVERRIDE_ATOMIC_[OPERATION]
 * is defined.  (The purpose of the APR_OVERRIDE_ATOMIC_* is
 * to allow a platform to declare an apr_atomic_*() function
 * with a different signature than the default.)
 */

#if !defined(apr_atomic_t)
#define apr_atomic_t apr_uint32_t
#endif

#if !defined(apr_atomic_init) && !defined(APR_OVERRIDE_ATOMIC_INIT)
apr_status_t apr_atomic_init(apr_pool_t *p);
#endif

#if !defined(apr_atomic_read) && !defined(APR_OVERRIDE_ATOMIC_READ)
#define apr_atomic_read(p)  *p
#endif

#if !defined(apr_atomic_set) && !defined(APR_OVERRIDE_ATOMIC_SET)
void apr_atomic_set(volatile apr_atomic_t *mem, apr_uint32_t val);
#define APR_ATOMIC_NEED_DEFAULT_INIT 1
#endif

#if !defined(apr_atomic_add) && !defined(APR_OVERRIDE_ATOMIC_ADD)
void apr_atomic_add(volatile apr_atomic_t *mem, apr_uint32_t val);
#define APR_ATOMIC_NEED_DEFAULT_INIT 1
#endif

#if !defined(apr_atomic_inc) && !defined(APR_OVERRIDE_ATOMIC_INC)
void apr_atomic_inc(volatile apr_atomic_t *mem);
#define APR_ATOMIC_NEED_DEFAULT_INIT 1
#endif

#if !defined(apr_atomic_dec) && !defined(APR_OVERRIDE_ATOMIC_DEC)
int apr_atomic_dec(volatile apr_atomic_t *mem);
#define APR_ATOMIC_NEED_DEFAULT_INIT 1
#endif

#if !defined(apr_atomic_cas) && !defined(APR_OVERRIDE_ATOMIC_CAS)
apr_uint32_t apr_atomic_cas(volatile apr_uint32_t *mem,long with,long cmp);
#define APR_ATOMIC_NEED_DEFAULT_INIT 1
#endif

#if !defined(apr_atomic_casptr) && !defined(APR_OVERRIDE_ATOMIC_CASPTR)
#if APR_SIZEOF_VOIDP == 4
#define apr_atomic_casptr(mem, with, cmp) (void *)apr_atomic_cas((apr_uint32_t *)(mem), (long)(with), (long)cmp)
#else
void *apr_atomic_casptr(volatile void **mem, void *with, const void *cmp);
#define APR_ATOMIC_NEED_DEFAULT_INIT 1
#endif
#endif

#ifndef APR_ATOMIC_NEED_DEFAULT_INIT
#define APR_ATOMIC_NEED_DEFAULT_INIT 0
#endif

/* If we're using the default versions of any of the atomic functions,
 * we'll need the atomic init to set up mutexes.  If a platform-specific
 * override above has replaced the atomic_init with a macro, it's an error.
 */
#if APR_ATOMIC_NEED_DEFAULT_INIT
#if defined(apr_atomic_init) || defined(APR_OVERRIDE_ATOMIC_INIT)
#error Platform has redefined apr_atomic_init, but other default default atomics require a default apr_atomic_init
#endif
#endif /* APR_ATOMIC_NEED_DEFAULT_INIT */

#endif /* !DOXYGEN */

/** @} */

#ifdef __cplusplus
}
#endif

#endif	/* !APR_ATOMIC_H */