upload android base code part3

android/bionic/libc/private/bionic_lock.h

@@ -0,0 +1,79 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ * 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.
+ *
+ * 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.
+ */
+#ifndef _BIONIC_LOCK_H
+#define _BIONIC_LOCK_H
+
+#include <stdatomic.h>
+#include "private/bionic_futex.h"
+#include "private/bionic_macros.h"
+
+// Lock is used in places like pthread_rwlock_t, which can be initialized without calling
+// an initialization function. So make sure Lock can be initialized by setting its memory to 0.
+class Lock {
+ private:
+  enum LockState {
+    Unlocked = 0,
+    LockedWithoutWaiter,
+    LockedWithWaiter,
+  };
+  _Atomic(LockState) state;
+  bool process_shared;
+
+ public:
+  void init(bool process_shared) {
+    atomic_init(&state, Unlocked);
+    this->process_shared = process_shared;
+  }
+
+  bool trylock() {
+    LockState old_state = Unlocked;
+    return __predict_true(atomic_compare_exchange_strong_explicit(&state, &old_state,
+                        LockedWithoutWaiter, memory_order_acquire, memory_order_relaxed));
+  }
+
+  void lock() {
+    LockState old_state = Unlocked;
+    if (__predict_true(atomic_compare_exchange_strong_explicit(&state, &old_state,
+                         LockedWithoutWaiter, memory_order_acquire, memory_order_relaxed))) {
+      return;
+    }
+    while (atomic_exchange_explicit(&state, LockedWithWaiter, memory_order_acquire) != Unlocked) {
+      // TODO: As the critical section is brief, it is a better choice to spin a few times befor sleeping.
+      __futex_wait_ex(&state, process_shared, LockedWithWaiter, false, nullptr);
+    }
+    return;
+  }
+
+  void unlock() {
+    if (atomic_exchange_explicit(&state, Unlocked, memory_order_release) == LockedWithWaiter) {
+      __futex_wake_ex(&state, process_shared, 1);
+    }
+  }
+};
+
+#endif  // _BIONIC_LOCK_H