split SmallLocks.h to get a larger portion of folly compiled on 32bit platforms

[folly.git] / folly / MicroSpinLock.h

diff --git a/folly/MicroSpinLock.h b/folly/MicroSpinLock.h
new file mode 100644 (file)
index 0000000..cccba15
--- /dev/null
+++ b/folly/MicroSpinLock.h
@@ -0,0 +1,143 @@
+/*
+ * Copyright 2015 Facebook, 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
+
+/*
+ * @author Keith Adams <kma@fb.com>
+ * @author Jordan DeLong <delong.j@fb.com>
+ */
+
+#include <array>
+#include <cinttypes>
+#include <type_traits>
+#include <boost/noncopyable.hpp>
+#include <cstdlib>
+#include <pthread.h>
+#include <mutex>
+#include <atomic>
+
+#include <glog/logging.h>
+#include <folly/detail/Sleeper.h>
+#include <folly/Portability.h>
+
+namespace folly {
+
+/*
+ * A really, *really* small spinlock for fine-grained locking of lots
+ * of teeny-tiny data.
+ *
+ * Zero initializing these is guaranteed to be as good as calling
+ * init(), since the free state is guaranteed to be all-bits zero.
+ *
+ * This class should be kept a POD, so we can used it in other packed
+ * structs (gcc does not allow __attribute__((__packed__)) on structs that
+ * contain non-POD data).  This means avoid adding a constructor, or
+ * making some members private, etc.
+ */
+struct MicroSpinLock {
+  enum { FREE = 0, LOCKED = 1 };
+  // lock_ can't be std::atomic<> to preserve POD-ness.
+  uint8_t lock_;
+
+  // Initialize this MSL.  It is unnecessary to call this if you
+  // zero-initialize the MicroSpinLock.
+  void init() {
+    payload()->store(FREE);
+  }
+
+  bool try_lock() {
+    return cas(FREE, LOCKED);
+  }
+
+  void lock() {
+    detail::Sleeper sleeper;
+    do {
+      while (payload()->load() != FREE) {
+        sleeper.wait();
+      }
+    } while (!try_lock());
+    DCHECK(payload()->load() == LOCKED);
+  }
+
+  void unlock() {
+    CHECK(payload()->load() == LOCKED);
+    payload()->store(FREE, std::memory_order_release);
+  }
+
+ private:
+  std::atomic<uint8_t>* payload() {
+    return reinterpret_cast<std::atomic<uint8_t>*>(&this->lock_);
+  }
+
+  bool cas(uint8_t compare, uint8_t newVal) {
+    return std::atomic_compare_exchange_strong_explicit(payload(), &compare, newVal,
+                                                        std::memory_order_acquire,
+                                                        std::memory_order_relaxed);
+  }
+};
+
+//////////////////////////////////////////////////////////////////////
+
+/**
+ * Array of spinlocks where each one is padded to prevent false sharing.
+ * Useful for shard-based locking implementations in environments where
+ * contention is unlikely.
+ */
+
+// TODO: generate it from configure (`getconf LEVEL1_DCACHE_LINESIZE`)
+#define FOLLY_CACHE_LINE_SIZE 64
+
+template <class T, size_t N>
+struct SpinLockArray {
+  T& operator[](size_t i) {
+    return data_[i].lock;
+  }
+
+  const T& operator[](size_t i) const {
+    return data_[i].lock;
+  }
+
+  constexpr size_t size() const { return N; }
+
+ private:
+  struct PaddedSpinLock {
+    PaddedSpinLock() : lock() {}
+    T lock;
+    char padding[FOLLY_CACHE_LINE_SIZE - sizeof(T)];
+  };
+  static_assert(sizeof(PaddedSpinLock) == FOLLY_CACHE_LINE_SIZE,
+                "Invalid size of PaddedSpinLock");
+
+  // Check if T can theoretically cross a cache line.
+  // NOTE: It should be alignof(std::max_align_t), but max_align_t
+  // isn't supported by gcc 4.6.2.
+  static_assert(alignof(MaxAlign) > 0 &&
+                FOLLY_CACHE_LINE_SIZE % alignof(MaxAlign) == 0 &&
+                sizeof(T) <= alignof(MaxAlign),
+                "T can cross cache line boundaries");
+
+  char padding_[FOLLY_CACHE_LINE_SIZE];
+  std::array<PaddedSpinLock, N> data_;
+} __attribute__((__aligned__));
+
+//////////////////////////////////////////////////////////////////////
+
+typedef std::lock_guard<MicroSpinLock> MSLGuard;
+
+//////////////////////////////////////////////////////////////////////
+
+}