diff --git a/libc/include/threads.h b/libc/include/threads.h
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+++ b/libc/include/threads.h
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+/*
+ * Copyright (C) 2019 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.
+ */
+
+#pragma once
+
+/**
+ * @file threads.h
+ * @brief C11 threads.
+ */
+
+#include <sys/cdefs.h>
+
+#include <pthread.h>
+#include <time.h>
+
+#define ONCE_FLAG_INIT PTHREAD_ONCE_INIT
+#define TSS_DTOR_ITERATIONS PTHREAD_DESTRUCTOR_ITERATIONS
+
+/** The type for a condition variable. */
+typedef pthread_cond_t cnd_t;
+/** The type for a thread. */
+typedef pthread_t thrd_t;
+/** The type for a thread-specific storage key. */
+typedef pthread_key_t tss_t;
+/** The type for a mutex. */
+typedef pthread_mutex_t mtx_t;
+
+/** The type for a thread-specific storage destructor. */
+typedef void (*tss_dtor_t)(void*);
+/** The type of the function passed to thrd_create() to create a new thread. */
+typedef int (*thrd_start_t)(void*);
+
+/** The type used by call_once(). */
+typedef pthread_once_t once_flag;
+
+enum {
+  mtx_plain = 0x1,
+  mtx_recursive = 0x2,
+  mtx_timed = 0x4,
+};
+
+enum {
+  thrd_success = 0,
+  thrd_busy = 1,
+  thrd_error = 2,
+  thrd_nomem = 3,
+  thrd_timedout = 4,
+};
+
+#if !defined(__cplusplus)
+#define thread_local _Thread_local
+#endif
+
+__BEGIN_DECLS
+
+#if __ANDROID_API__ >= __ANDROID_API_R__
+// This file is implemented as static inlines before API level 30.
+
+/** Uses `__flag` to ensure that `__function` is called exactly once. */
+void call_once(once_flag* __flag, void (*__function)(void));
+
+
+
+/**
+ * Unblocks all threads blocked on `__cond`.
+ */
+int cnd_broadcast(cnd_t* __cond);
+
+/**
+ * Destroys a condition variable.
+ */
+void cnd_destroy(cnd_t* __cond);
+
+/**
+ * Creates a condition variable.
+ */
+int cnd_init(cnd_t* __cond);
+
+/**
+ * Unblocks one thread blocked on `__cond`.
+ */
+int cnd_signal(cnd_t* __cond);
+
+/**
+ * Unlocks `__mutex` and blocks until `__cond` is signaled or `__timeout` occurs.
+ */
+int cnd_timedwait(cnd_t* __cond, mtx_t* __mutex, const struct timespec* __timeout);
+
+/**
+ * Unlocks `__mutex` and blocks until `__cond` is signaled.
+ */
+int cnd_wait(cnd_t* __cond, mtx_t* __mutex);
+
+
+
+/**
+ * Destroys a mutex.
+ */
+void mtx_destroy(mtx_t* __mutex);
+
+/**
+ * Creates a mutex.
+ */
+int mtx_init(mtx_t* __mutex, int __type);
+
+/**
+ * Blocks until `__mutex` is acquired.
+ */
+int mtx_lock(mtx_t* __mutex);
+
+/**
+ * Blocks until `__mutex` is acquired or `__timeout` expires.
+ */
+int mtx_timedlock(mtx_t* __mutex, const struct timespec* __timeout);
+
+/**
+ * Acquires `__mutex` or returns `thrd_busy`.
+ */
+int mtx_trylock(mtx_t* __mutex);
+
+/**
+ * Unlocks `__mutex`.
+ */
+int mtx_unlock(mtx_t* __mutex);
+
+
+
+/**
+ * Creates a new thread running `__function(__arg)`, and sets `*__thrd` to
+ * the new thread.
+ */
+int thrd_create(thrd_t* __thrd, thrd_start_t __function, void* __arg);
+
+/**
+ * Returns the `thrd_t` corresponding to the caller.
+ */
+thrd_t thrd_current(void);
+
+/**
+ * Tells the OS to automatically dispose of `__thrd` when it exits.
+ */
+int thrd_detach(thrd_t __thrd);
+
+/**
+ * Tests whether two threads are the same thread.
+ */
+int thrd_equal(thrd_t __lhs, thrd_t __rhs);
+
+/**
+ * Terminates the calling thread, setting its result to `__result`.
+ */
+void thrd_exit(int __result) __noreturn;
+
+/**
+ * Blocks until `__thrd` terminates. If `__result` is not null, `*__result`
+ * is set to the exiting thread's result.
+ */
+int thrd_join(thrd_t __thrd, int* __result);
+
+/**
+ * Blocks the caller for at least `__duration` unless a signal is delivered.
+ * If a signal causes the sleep to end early and `__remaining` is not null,
+ * `*__remaining` is set to the time remaining.
+ *
+ * Returns 0 on success, or -1 if a signal was delivered.
+ */
+int thrd_sleep(const struct timespec* __duration, struct timespec* __remaining);
+
+/**
+ * Request that other threads should be scheduled.
+ */
+void thrd_yield(void);
+
+
+
+/**
+ * Creates a thread-specific storage key with the associated destructor (which
+ * may be null).
+ */
+int tss_create(tss_t* __key, tss_dtor_t __dtor);
+
+/**
+ * Destroys a thread-specific storage key.
+ */
+void tss_delete(tss_t __key);
+
+/**
+ * Returns the value for the current thread held in the thread-specific storage
+ * identified by `__key`.
+ */
+void* tss_get(tss_t __key);
+
+/**
+ * Sets the current thread's value for the thread-specific storage identified
+ * by `__key` to `__value`.
+ */
+int tss_set(tss_t __key, void* __value);
+
+#endif
+
+__END_DECLS
+
+#include <android/legacy_threads_inlines.h>