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view src/dbinc/atomic.h @ 0:a1985f14b030
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author | chegar |
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date | Fri, 11 May 2012 10:42:02 +0100 |
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/* * See the file LICENSE for redistribution information. * * Copyright (c) 2009, 2012 Oracle and/or its affiliates. All rights reserved. * * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code 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 General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. * * $Id$ */ #ifndef _DB_ATOMIC_H_ #define _DB_ATOMIC_H_ #if defined(__cplusplus) extern "C" { #endif /* * Atomic operation support for Oracle Berkeley DB * * HAVE_ATOMIC_SUPPORT configures whether to use the assembly language * or system calls to perform: * * atomic_inc(env, valueptr) * Adds 1 to the db_atomic_t value, returning the new value. * * atomic_dec(env, valueptr) * Subtracts 1 from the db_atomic_t value, returning the new value. * * atomic_compare_exchange(env, valueptr, oldval, newval) * If the db_atomic_t's value is still oldval, set it to newval. * It returns 1 for success or 0 for failure. * * The ENV * parameter is used only when HAVE_ATOMIC_SUPPORT is undefined. * * If the platform does not natively support any one of these operations, * then atomic operations will be emulated with this sequence: * MUTEX_LOCK() * <op> * MUTEX_UNLOCK(); * Uses where mutexes are not available (e.g. the environment has not yet * attached to the mutex region) must be avoided. */ #if defined(DB_WIN32) typedef DWORD atomic_value_t; #else typedef int32_t atomic_value_t; #endif /* * Windows CE has strange issues using the Interlocked APIs with variables * stored in shared memory. It seems like the page needs to have been written * prior to the API working as expected. Work around this by allocating an * additional 32-bit value that can be harmlessly written for each value * used in Interlocked instructions. */ #if defined(DB_WINCE) typedef struct { volatile atomic_value_t value; volatile atomic_value_t dummy; } db_atomic_t; #else typedef struct { volatile atomic_value_t value; } db_atomic_t; #endif /* * These macro hide the db_atomic_t structure layout and help detect * non-atomic_t actual argument to the atomic_xxx() calls. DB requires * aligned 32-bit reads to be atomic even outside of explicit 'atomic' calls. * These have no memory barriers; the caller must include them when necessary. */ #define atomic_read(p) ((p)->value) #define atomic_init(p, val) ((p)->value = (val)) #ifdef HAVE_ATOMIC_SUPPORT #if defined(DB_WIN32) #if defined(DB_WINCE) #define WINCE_ATOMIC_MAGIC(p) \ /* \ * Memory mapped regions on Windows CE cause problems with \ * InterlockedXXX calls. Each page in a mapped region needs to \ * have been written to prior to an InterlockedXXX call, or the \ * InterlockedXXX call hangs. This does not seem to be \ * documented anywhere. For now, read/write a non-critical \ * piece of memory from the shared region prior to attempting \ * shared region prior to attempting an InterlockedExchange \ * InterlockedXXX operation. \ */ \ (p)->dummy = 0 #else #define WINCE_ATOMIC_MAGIC(p) 0 #endif #if defined(DB_WINCE) || (defined(_MSC_VER) && _MSC_VER < 1300) /* * The Interlocked instructions on Windows CE have different parameter * definitions. The parameters lost their 'volatile' qualifier, * cast it away, to avoid compiler warnings. * These definitions should match those in dbinc/mutex_int.h for tsl_t, except * that the WINCE version drops the volatile qualifier. */ typedef PLONG interlocked_val; #define atomic_inc(env, p) \ (WINCE_ATOMIC_MAGIC(p), \ InterlockedIncrement((interlocked_val)(&(p)->value))) #else typedef LONG volatile *interlocked_val; #define atomic_inc(env, p) \ InterlockedIncrement((interlocked_val)(&(p)->value)) #endif #define atomic_dec(env, p) \ (WINCE_ATOMIC_MAGIC(p), \ InterlockedDecrement((interlocked_val)(&(p)->value))) #if defined(_MSC_VER) && _MSC_VER < 1300 #define atomic_compare_exchange(env, p, oldval, newval) \ (WINCE_ATOMIC_MAGIC(p), \ (InterlockedCompareExchange((PVOID *)(&(p)->value), \ (PVOID)(newval), (PVOID)(oldval)) == (PVOID)(oldval))) #else #define atomic_compare_exchange(env, p, oldval, newval) \ (WINCE_ATOMIC_MAGIC(p), \ (InterlockedCompareExchange((interlocked_val)(&(p)->value), \ (newval), (oldval)) == (oldval))) #endif #endif #if defined(HAVE_ATOMIC_SOLARIS) /* Solaris sparc & x86/64 */ #include <atomic.h> #define atomic_inc(env, p) \ atomic_inc_uint_nv((volatile unsigned int *) &(p)->value) #define atomic_dec(env, p) \ atomic_dec_uint_nv((volatile unsigned int *) &(p)->value) #define atomic_compare_exchange(env, p, oval, nval) \ (atomic_cas_32((volatile unsigned int *) &(p)->value, \ (oval), (nval)) == (oval)) #endif #if defined(HAVE_ATOMIC_X86_GCC_ASSEMBLY) /* x86/x86_64 gcc */ #define atomic_inc(env, p) __atomic_inc(p) #define atomic_dec(env, p) __atomic_dec(p) #define atomic_compare_exchange(env, p, o, n) \ __atomic_compare_exchange((p), (o), (n)) static inline int __atomic_inc(db_atomic_t *p) { int temp; temp = 1; __asm__ __volatile__("lock; xadd %0, (%1)" : "+r"(temp) : "r"(p)); return (temp + 1); } static inline int __atomic_dec(db_atomic_t *p) { int temp; temp = -1; __asm__ __volatile__("lock; xadd %0, (%1)" : "+r"(temp) : "r"(p)); return (temp - 1); } /* * x86/gcc Compare exchange for shared latches. i486+ * Returns 1 for success, 0 for failure * * GCC 4.1+ has an equivalent __sync_bool_compare_and_swap() as well as * __sync_val_compare_and_swap() which returns the value read from *dest * http://gcc.gnu.org/onlinedocs/gcc-4.1.0/gcc/Atomic-Builtins.html * which configure could be changed to use. */ static inline int __atomic_compare_exchange( db_atomic_t *p, atomic_value_t oldval, atomic_value_t newval) { atomic_value_t was; if (p->value != oldval) /* check without expensive cache line locking */ return 0; __asm__ __volatile__("lock; cmpxchgl %1, (%2);" :"=a"(was) :"r"(newval), "r"(p), "a"(oldval) :"memory", "cc"); return (was == oldval); } #endif #else /* * No native hardware support for atomic increment, decrement, and * compare-exchange. Emulate them when mutexes are supported; * do them without concern for atomicity when no mutexes. */ #ifndef HAVE_MUTEX_SUPPORT /* * These minimal versions are correct to use only for single-threaded, * single-process environments. */ #define atomic_inc(env, p) (++(p)->value) #define atomic_dec(env, p) (--(p)->value) #define atomic_compare_exchange(env, p, oldval, newval) \ (DB_ASSERT(env, atomic_read(p) == (oldval)), \ atomic_init(p, (newval)), 1) #else #define atomic_inc(env, p) __atomic_inc(env, p) #define atomic_dec(env, p) __atomic_dec(env, p) #endif #endif #if defined(__cplusplus) } #endif #endif /* !_DB_ATOMIC_H_ */