/*
- * Copyright 2015 Facebook, Inc.
+ * Copyright 2015-present Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* limitations under the License.
*/
+/*
+ * N.B. You most likely do _not_ want to use PicoSpinLock or any other
+ * kind of spinlock. Consider MicroLock instead.
+ *
+ * In short, spinlocks in preemptive multi-tasking operating systems
+ * have serious problems and fast mutexes like std::mutex are almost
+ * certainly the better choice, because letting the OS scheduler put a
+ * thread to sleep is better for system responsiveness and throughput
+ * than wasting a timeslice repeatedly querying a lock held by a
+ * thread that's blocked, and you can't prevent userspace
+ * programs blocking.
+ *
+ * Spinlocks in an operating system kernel make much more sense than
+ * they do in userspace.
+ */
+
#pragma once
+#define FOLLY_PICO_SPIN_LOCK_H_
/*
* @author Keith Adams <kma@fb.com>
*/
#include <array>
+#include <atomic>
#include <cinttypes>
-#include <type_traits>
#include <cstdlib>
-#include <pthread.h>
#include <mutex>
-#include <atomic>
+#include <type_traits>
#include <glog/logging.h>
-#include <folly/detail/Sleeper.h>
+
#include <folly/Portability.h>
+#include <folly/synchronization/detail/Sleeper.h>
-#if !FOLLY_X64 && !FOLLY_A64 && !FOLLY_PPC64
-# error "PicoSpinLock.h is currently x64, aarch64 and ppc64 only."
+#if !FOLLY_X64 && !FOLLY_AARCH64 && !FOLLY_PPC64
+#error "PicoSpinLock.h is currently x64, aarch64 and ppc64 only."
#endif
namespace folly {
* have a real constructor because we want this to be a POD type so we
* can put it into packed structs.
*/
-template<class IntType, int Bit = sizeof(IntType) * 8 - 1>
+template <class IntType, int Bit = sizeof(IntType) * 8 - 1>
struct PicoSpinLock {
// Internally we deal with the unsigned version of the type.
typedef typename std::make_unsigned<IntType>::type UIntType;
public:
static const UIntType kLockBitMask_ = UIntType(1) << Bit;
- UIntType lock_;
+ mutable UIntType lock_;
/*
* You must call this function before using this class, if you
*/
void init(IntType initialValue = 0) {
CHECK(!(initialValue & kLockBitMask_));
- lock_ = initialValue;
+ reinterpret_cast<std::atomic<UIntType>*>(&lock_)->store(
+ UIntType(initialValue), std::memory_order_release);
}
/*
* as you normally get.)
*/
IntType getData() const {
- return static_cast<IntType>(lock_ & ~kLockBitMask_);
+ auto res = reinterpret_cast<std::atomic<UIntType>*>(&lock_)->load(
+ std::memory_order_relaxed) &
+ ~kLockBitMask_;
+ return res;
}
/*
*/
void setData(IntType w) {
CHECK(!(w & kLockBitMask_));
- lock_ = (lock_ & kLockBitMask_) | w;
+ auto l = reinterpret_cast<std::atomic<UIntType>*>(&lock_);
+ l->store(
+ (l->load(std::memory_order_relaxed) & kLockBitMask_) | w,
+ std::memory_order_relaxed);
}
/*
bool try_lock() const {
bool ret = false;
-#if FOLLY_X64
+#if defined(FOLLY_SANITIZE_THREAD)
+ // TODO: Might be able to fully move to std::atomic when gcc emits lock btr:
+ // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49244
+ ret =
+ !(reinterpret_cast<std::atomic<UIntType>*>(&lock_)->fetch_or(
+ kLockBitMask_, std::memory_order_acquire) &
+ kLockBitMask_);
+#elif _MSC_VER
+ switch (sizeof(IntType)) {
+ case 2:
+ // There is no _interlockedbittestandset16 for some reason :(
+ ret = _InterlockedOr16(
+ (volatile short*)&lock_, (short)kLockBitMask_) & kLockBitMask_;
+ break;
+ case 4:
+ ret = _interlockedbittestandset((volatile long*)&lock_, Bit);
+ break;
+ case 8:
+ ret = _interlockedbittestandset64((volatile long long*)&lock_, Bit);
+ break;
+ }
+#elif FOLLY_X64
#define FB_DOBTS(size) \
asm volatile("lock; bts" #size " %1, (%2); setnc %0" \
: "=r" (ret) \
}
#undef FB_DOBTS
-#elif FOLLY_A64
- ret = __atomic_fetch_or(&lock_, 1 << Bit, __ATOMIC_SEQ_CST);
+#elif FOLLY_AARCH64
+ using SIntType = typename std::make_signed<UIntType>::type;
+ auto const lock = reinterpret_cast<SIntType*>(&lock_);
+ auto const mask = static_cast<SIntType>(kLockBitMask_);
+ return !(mask & __atomic_fetch_or(lock, mask, __ATOMIC_ACQUIRE));
#elif FOLLY_PPC64
#define FB_DOBTS(size) \
asm volatile("\teieio\n" \
* integer.
*/
void unlock() const {
-#if FOLLY_X64
+#ifdef _MSC_VER
+ switch (sizeof(IntType)) {
+ case 2:
+ // There is no _interlockedbittestandreset16 for some reason :(
+ _InterlockedAnd16((volatile short*)&lock_, (short)~kLockBitMask_);
+ break;
+ case 4:
+ _interlockedbittestandreset((volatile long*)&lock_, Bit);
+ break;
+ case 8:
+ _interlockedbittestandreset64((volatile long long*)&lock_, Bit);
+ break;
+ }
+#elif FOLLY_X64
#define FB_DOBTR(size) \
asm volatile("lock; btr" #size " %0, (%1)" \
: \
}
#undef FB_DOBTR
-#elif FOLLY_A64
- __atomic_fetch_and(&lock_, ~(1 << Bit), __ATOMIC_SEQ_CST);
+#elif FOLLY_AARCH64
+ using SIntType = typename std::make_signed<UIntType>::type;
+ auto const lock = reinterpret_cast<SIntType*>(&lock_);
+ auto const mask = static_cast<SIntType>(kLockBitMask_);
+ __atomic_fetch_and(lock, ~mask, __ATOMIC_RELEASE);
#elif FOLLY_PPC64
#define FB_DOBTR(size) \
asm volatile("\teieio\n" \
}
};
-}
+} // namespace folly
projects / folly.git / blobdiff