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// atomic_int.h
// atomic wrapper for unsigned
/* Copyright 2009 10gen Inc.
*
* 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.
*/
#pragma once
#if defined(_WIN32)
#include "mongo/platform/windows_basic.h"
#endif
#include "mongo/platform/compiler.h"
namespace mongo {
/**
* An unsigned integer supporting atomic read-modify-write operations.
*
* Many operations on these types depend on natural alignment (4 byte alignment for 4-byte
* words, i.e.).
*/
struct MONGO_COMPILER_ALIGN_TYPE( 4 ) AtomicUInt {
AtomicUInt() : x(0) {}
AtomicUInt(unsigned z) : x(z) { }
operator unsigned() const { return x; }
unsigned get() const { return x; }
inline void set(unsigned newX);
inline AtomicUInt operator++(); // ++prefix
inline AtomicUInt operator++(int);// postfix++
inline AtomicUInt operator--(); // --prefix
inline AtomicUInt operator--(int); // postfix--
inline void signedAdd(int by);
inline void zero() { set(0); }
volatile unsigned x;
};
#if defined(_WIN32)
void AtomicUInt::set(unsigned newX) {
InterlockedExchange((volatile long *)&x, newX);
}
AtomicUInt AtomicUInt::operator++() {
return InterlockedIncrement((volatile long*)&x);
}
AtomicUInt AtomicUInt::operator++(int) {
return InterlockedIncrement((volatile long*)&x)-1;
}
AtomicUInt AtomicUInt::operator--() {
return InterlockedDecrement((volatile long*)&x);
}
AtomicUInt AtomicUInt::operator--(int) {
return InterlockedDecrement((volatile long*)&x)+1;
}
# if defined(_WIN64)
// don't see an InterlockedAdd for _WIN32...hmmm
void AtomicUInt::signedAdd(int by) {
InterlockedAdd((volatile long *)&x,by);
}
# endif
#elif defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4)
// this is in GCC >= 4.1
inline void AtomicUInt::set(unsigned newX) { __sync_synchronize(); x = newX; }
AtomicUInt AtomicUInt::operator++() {
return __sync_add_and_fetch(&x, 1);
}
AtomicUInt AtomicUInt::operator++(int) {
return __sync_fetch_and_add(&x, 1);
}
AtomicUInt AtomicUInt::operator--() {
return __sync_add_and_fetch(&x, -1);
}
AtomicUInt AtomicUInt::operator--(int) {
return __sync_fetch_and_add(&x, -1);
}
void AtomicUInt::signedAdd(int by) {
__sync_fetch_and_add(&x, by);
}
#elif defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
inline void AtomicUInt::set(unsigned newX) {
asm volatile("mfence" ::: "memory");
x = newX;
}
// from boost 1.39 interprocess/detail/atomic.hpp
inline unsigned atomic_int_helper(volatile unsigned *x, int val) {
int r;
asm volatile
(
"lock\n\t"
"xadd %1, %0":
"+m"( *x ), "=r"( r ): // outputs (%0, %1)
"1"( val ): // inputs (%2 == %1)
"memory", "cc" // clobbers
);
return r;
}
AtomicUInt AtomicUInt::operator++() {
return atomic_int_helper(&x, 1)+1;
}
AtomicUInt AtomicUInt::operator++(int) {
return atomic_int_helper(&x, 1);
}
AtomicUInt AtomicUInt::operator--() {
return atomic_int_helper(&x, -1)-1;
}
AtomicUInt AtomicUInt::operator--(int) {
return atomic_int_helper(&x, -1);
}
void AtomicUInt::signedAdd(int by) {
atomic_int_helper(&x, by);
}
#else
# error "unsupported compiler or platform"
#endif
} // namespace mongo
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