Always use CLOCK_MONOTONIC for pthreads and semaphores
pthread's and semaphore's default behavior is to use CLOCK_REALTIME,
however this behavior is essentially never intended, as that clock is
prone to change discontinuously.
What users really intend is to use CLOCK_MONOTONIC, however only
pthread_cond_timedwait() provides this as an option and even there, a
large amount of existing code does not opt into CLOCK_MONOTONIC.
We have seen numerous bugs directly attributable to this difference.
Therefore, we provide this general workaround to always use
CLOCK_MONOTONIC for waiting, regardless of what the input timespec
is.
Specifically this impacts the below APIs:
pthread_mutex_timedlock()
pthread_cond_timedwait()
pthread_rwlock_timedrdlock()
pthread_rwlock_timedwrlock()
sem_timedwait()
Test: boot bullhead, boot sailfish
Test: bionic pthread/semaphore unit tests
Test: check that pthread_cond_timedwait() timeouts are uneffected by
CLOCK_REALTIME time changes
Bug: 64694413
Bug: 64623895
Bug: 35756266
Bug: 35678943
Change-Id: Ibba98f5d88be1c306d14e9b9366302ecbef6d534
diff --git a/libc/bionic/bionic_futex.cpp b/libc/bionic/bionic_futex.cpp
new file mode 100644
index 0000000..dd66e40
--- /dev/null
+++ b/libc/bionic/bionic_futex.cpp
@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2017 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 "private/bionic_futex.h"
+
+#include <time.h>
+
+#include "private/bionic_time_conversions.h"
+
+int __futex_wait_ex(volatile void* ftx, bool shared, int value, bool use_realtime_clock,
+ const timespec* abs_timeout) {
+ const timespec* futex_abs_timeout = abs_timeout;
+ // pthread's and semaphore's default behavior is to use CLOCK_REALTIME, however this behavior is
+ // essentially never intended, as that clock is prone to change discontinuously.
+ //
+ // What users really intend is to use CLOCK_MONOTONIC, however only pthread_cond_timedwait()
+ // provides this as an option and even there, a large amount of existing code does not opt into
+ // CLOCK_MONOTONIC.
+ //
+ // We have seen numerous bugs directly attributable to this difference. Therefore, we provide
+ // this general workaround to always use CLOCK_MONOTONIC for waiting, regardless of what the input
+ // timespec is.
+ timespec converted_monotonic_abs_timeout;
+ if (abs_timeout && use_realtime_clock) {
+ monotonic_time_from_realtime_time(converted_monotonic_abs_timeout, *abs_timeout);
+ if (converted_monotonic_abs_timeout.tv_sec < 0) {
+ return -ETIMEDOUT;
+ }
+ futex_abs_timeout = &converted_monotonic_abs_timeout;
+ }
+
+ return __futex(ftx, (shared ? FUTEX_WAIT_BITSET : FUTEX_WAIT_BITSET_PRIVATE), value,
+ futex_abs_timeout, FUTEX_BITSET_MATCH_ANY);
+}