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// Copyright (c) 2005, 2006, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// ---
// Author: Sanjay Ghemawat <opensource@google.com>
#ifndef TCMALLOC_INTERNAL_SPINLOCK_H__
#define TCMALLOC_INTERNAL_SPINLOCK_H__
#if (CPU(X86) || CPU(X86_64) || CPU(PPC)) && (COMPILER(GCC) || COMPILER(MSVC))
#include <time.h> /* For nanosleep() */
#include <sched.h> /* For sched_yield() */
#if HAVE(STDINT_H)
#include <stdint.h>
#elif HAVE(INTTYPES_H)
#include <inttypes.h>
#else
#include <sys/types.h>
#endif
#if OS(WINDOWS)
#ifndef WIN32_LEAN_AND_MEAN
#define WIN32_LEAN_AND_MEAN
#endif
#include <windows.h>
#endif
static void TCMalloc_SlowLock(volatile unsigned int* lockword);
// The following is a struct so that it can be initialized at compile time
struct TCMalloc_SpinLock {
inline void Lock() {
int r;
#if COMPILER(GCC)
#if CPU(X86) || CPU(X86_64)
__asm__ __volatile__
("xchgl %0, %1"
: "=r"(r), "=m"(lockword_)
: "0"(1), "m"(lockword_)
: "memory");
#else
volatile unsigned int *lockword_ptr = &lockword_;
__asm__ __volatile__
("1: lwarx %0, 0, %1\n\t"
"stwcx. %2, 0, %1\n\t"
"bne- 1b\n\t"
"isync"
: "=&r" (r), "=r" (lockword_ptr)
: "r" (1), "1" (lockword_ptr)
: "memory");
#endif
#elif COMPILER(MSVC)
__asm {
mov eax, this ; store &lockword_ (which is this+0) in eax
mov ebx, 1 ; store 1 in ebx
xchg [eax], ebx ; exchange lockword_ and 1
mov r, ebx ; store old value of lockword_ in r
}
#endif
if (r) TCMalloc_SlowLock(&lockword_);
}
inline void Unlock() {
#if COMPILER(GCC)
#if CPU(X86) || CPU(X86_64)
__asm__ __volatile__
("movl $0, %0"
: "=m"(lockword_)
: "m" (lockword_)
: "memory");
#else
__asm__ __volatile__
("isync\n\t"
"eieio\n\t"
"stw %1, %0"
#if OS(DARWIN) || CPU(PPC)
: "=o" (lockword_)
#else
: "=m" (lockword_)
#endif
: "r" (0)
: "memory");
#endif
#elif COMPILER(MSVC)
__asm {
mov eax, this ; store &lockword_ (which is this+0) in eax
mov [eax], 0 ; set lockword_ to 0
}
#endif
}
// Report if we think the lock can be held by this thread.
// When the lock is truly held by the invoking thread
// we will always return true.
// Indended to be used as CHECK(lock.IsHeld());
inline bool IsHeld() const {
return lockword_ != 0;
}
inline void Init() { lockword_ = 0; }
volatile unsigned int lockword_;
};
#define SPINLOCK_INITIALIZER { 0 }
static void TCMalloc_SlowLock(volatile unsigned int* lockword) {
sched_yield(); // Yield immediately since fast path failed
while (true) {
int r;
#if COMPILER(GCC)
#if CPU(X86) || CPU(X86_64)
__asm__ __volatile__
("xchgl %0, %1"
: "=r"(r), "=m"(*lockword)
: "0"(1), "m"(*lockword)
: "memory");
#else
int tmp = 1;
__asm__ __volatile__
("1: lwarx %0, 0, %1\n\t"
"stwcx. %2, 0, %1\n\t"
"bne- 1b\n\t"
"isync"
: "=&r" (r), "=r" (lockword)
: "r" (tmp), "1" (lockword)
: "memory");
#endif
#elif COMPILER(MSVC)
__asm {
mov eax, lockword ; assign lockword into eax
mov ebx, 1 ; assign 1 into ebx
xchg [eax], ebx ; exchange *lockword and 1
mov r, ebx ; store old value of *lockword in r
}
#endif
if (!r) {
return;
}
// This code was adapted from the ptmalloc2 implementation of
// spinlocks which would sched_yield() upto 50 times before
// sleeping once for a few milliseconds. Mike Burrows suggested
// just doing one sched_yield() outside the loop and always
// sleeping after that. This change helped a great deal on the
// performance of spinlocks under high contention. A test program
// with 10 threads on a dual Xeon (four virtual processors) went
// from taking 30 seconds to 16 seconds.
// Sleep for a few milliseconds
#if OS(WINDOWS)
Sleep(2);
#else
struct timespec tm;
tm.tv_sec = 0;
tm.tv_nsec = 2000001;
nanosleep(&tm, NULL);
#endif
}
}
#else
#include <pthread.h>
// Portable version
struct TCMalloc_SpinLock {
pthread_mutex_t private_lock_;
inline void Init() {
if (pthread_mutex_init(&private_lock_, NULL) != 0) CRASH();
}
inline void Finalize() {
if (pthread_mutex_destroy(&private_lock_) != 0) CRASH();
}
inline void Lock() {
if (pthread_mutex_lock(&private_lock_) != 0) CRASH();
}
inline void Unlock() {
if (pthread_mutex_unlock(&private_lock_) != 0) CRASH();
}
bool IsHeld() {
if (pthread_mutex_trylock(&private_lock_))
return true;
Unlock();
return false;
}
};
#define SPINLOCK_INITIALIZER { PTHREAD_MUTEX_INITIALIZER }
#endif
// Corresponding locker object that arranges to acquire a spinlock for
// the duration of a C++ scope.
class TCMalloc_SpinLockHolder {
private:
TCMalloc_SpinLock* lock_;
public:
inline explicit TCMalloc_SpinLockHolder(TCMalloc_SpinLock* l)
: lock_(l) { l->Lock(); }
inline ~TCMalloc_SpinLockHolder() { lock_->Unlock(); }
};
// Short-hands for convenient use by tcmalloc.cc
typedef TCMalloc_SpinLock SpinLock;
typedef TCMalloc_SpinLockHolder SpinLockHolder;
#endif // TCMALLOC_INTERNAL_SPINLOCK_H__
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