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

[folly.git] / folly / detail / Sleeper.h

diff --git a/folly/detail/Sleeper.h b/folly/detail/Sleeper.h
new file mode 100644 (file)
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--- /dev/null
+++ b/folly/detail/Sleeper.h
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+/*
+ * 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 <cinttypes>
+#include <ctime>
+
+#include <folly/Portability.h>
+
+namespace folly {
+
+//////////////////////////////////////////////////////////////////////
+
+namespace detail {
+
+  /*
+   * A helper object for the contended case. Starts off with eager
+   * spinning, and falls back to sleeping for small quantums.
+   */
+  class Sleeper {
+    static const uint32_t kMaxActiveSpin = 4000;
+
+    uint32_t spinCount;
+
+  public:
+    Sleeper() : spinCount(0) {}
+
+    void wait() {
+      if (spinCount < kMaxActiveSpin) {
+        ++spinCount;
+        asm_volatile_pause();
+      } else {
+        /*
+         * Always sleep 0.5ms, assuming this will make the kernel put
+         * us down for whatever its minimum timer resolution is (in
+         * linux this varies by kernel version from 1ms to 10ms).
+         */
+        struct timespec ts = { 0, 500000 };
+        nanosleep(&ts, nullptr);
+      }
+    }
+  };
+
+}
+}