diff --git a/libc/bionic/pthread_once.cpp b/libc/bionic/pthread_once.cpp
new file mode 100644
index 0000000..6d9d7d1
--- /dev/null
+++ b/libc/bionic/pthread_once.cpp
@@ -0,0 +1,100 @@
+/*
+ * Copyright (C) 2008 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.
+ */
+
+#include <pthread.h>
+
+#include "private/bionic_atomic_inline.h"
+#include "private/bionic_futex.h"
+
+#define ONCE_INITIALIZING           (1 << 0)
+#define ONCE_COMPLETED              (1 << 1)
+
+/* NOTE: this implementation doesn't support a init function that throws a C++ exception
+ *       or calls fork()
+ */
+int pthread_once(pthread_once_t* once_control, void (*init_routine)(void)) {
+  volatile pthread_once_t* once_control_ptr = once_control;
+
+  // PTHREAD_ONCE_INIT is 0, we use the following bit flags
+  //   bit 0 set  -> initialization is under way
+  //   bit 1 set  -> initialization is complete
+
+  // First check if the once is already initialized. This will be the common
+  // case and we want to make this as fast as possible. Note that this still
+  // requires a load_acquire operation here to ensure that all the
+  // stores performed by the initialization function are observable on
+  // this CPU after we exit.
+  if (__predict_true((*once_control_ptr & ONCE_COMPLETED) != 0)) {
+    ANDROID_MEMBAR_FULL();
+    return 0;
+  }
+
+  while (true) {
+    // Try to atomically set the INITIALIZING flag.
+    // This requires a cmpxchg loop, and we may need
+    // to exit prematurely if we detect that
+    // COMPLETED is now set.
+    int32_t  old_value, new_value;
+
+    do {
+      old_value = *once_control_ptr;
+      if ((old_value & ONCE_COMPLETED) != 0) {
+        break;
+      }
+
+      new_value = old_value | ONCE_INITIALIZING;
+    } while (__bionic_cmpxchg(old_value, new_value, once_control_ptr) != 0);
+
+    if ((old_value & ONCE_COMPLETED) != 0) {
+      // We detected that COMPLETED was set while in our loop.
+      ANDROID_MEMBAR_FULL();
+      return 0;
+    }
+
+    if ((old_value & ONCE_INITIALIZING) == 0) {
+      // We got there first, we can jump out of the loop to handle the initialization.
+      break;
+    }
+
+    // Another thread is running the initialization and hasn't completed
+    // yet, so wait for it, then try again.
+    __futex_wait_ex(once_control_ptr, 0, old_value, NULL);
+  }
+
+  // Call the initialization function.
+  (*init_routine)();
+
+  // Do a store_release indicating that initialization is complete.
+  ANDROID_MEMBAR_FULL();
+  *once_control_ptr = ONCE_COMPLETED;
+
+  // Wake up any waiters, if any.
+  __futex_wake_ex(once_control_ptr, 0, INT_MAX);
+
+  return 0;
+}