/*
- * Copyright 2015 Facebook, Inc.
+ * Copyright 2017 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 MicroSpinLock 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
/*
*/
#include <array>
-#include <cinttypes>
-#include <type_traits>
-#include <boost/noncopyable.hpp>
-#include <cstdlib>
-#include <pthread.h>
-#include <mutex>
#include <atomic>
+#include <cassert>
+#include <cstdint>
+#include <mutex>
+#include <type_traits>
-#include <glog/logging.h>
-#include <folly/detail/Sleeper.h>
#include <folly/Portability.h>
+#include <folly/lang/Align.h>
+#include <folly/synchronization/detail/Sleeper.h>
namespace folly {
sleeper.wait();
}
} while (!try_lock());
- DCHECK(payload()->load() == LOCKED);
+ assert(payload()->load() == LOCKED);
}
void unlock() {
- CHECK(payload()->load() == LOCKED);
+ assert(payload()->load() == LOCKED);
payload()->store(FREE, std::memory_order_release);
}
std::memory_order_relaxed);
}
};
+static_assert(
+ std::is_pod<MicroSpinLock>::value,
+ "MicroSpinLock must be kept a POD type.");
//////////////////////////////////////////////////////////////////////
#define FOLLY_CACHE_LINE_SIZE 64
template <class T, size_t N>
-struct FOLLY_ALIGNED_MAX SpinLockArray {
+struct alignas(max_align_v) SpinLockArray {
T& operator[](size_t i) {
return data_[i].lock;
}
"Invalid size of PaddedSpinLock");
// Check if T can theoretically cross a cache line.
- static_assert(alignof(std::max_align_t) > 0 &&
- FOLLY_CACHE_LINE_SIZE % alignof(std::max_align_t) == 0 &&
- sizeof(T) <= alignof(std::max_align_t),
- "T can cross cache line boundaries");
+ static_assert(
+ max_align_v > 0 && FOLLY_CACHE_LINE_SIZE % max_align_v == 0 &&
+ sizeof(T) <= max_align_v,
+ "T can cross cache line boundaries");
char padding_[FOLLY_CACHE_LINE_SIZE];
std::array<PaddedSpinLock, N> data_;
//////////////////////////////////////////////////////////////////////
-}
+} // namespace folly