--- /dev/null
+/*
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ *
+ * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * Userspace RCU library - sys_futex compatibility code
+ */
+
+#include <stdio.h>
+#include <pthread.h>
+#include <signal.h>
+#include <assert.h>
+#include <errno.h>
+#include <poll.h>
+#include <stdint.h>
+
+#include <urcu/arch.h>
+#include <urcu/system.h>
+
+#include "lib/lttng-ust/futex.h"
+
+/*
+ * This compat header originated in userspace RCU where it's used across
+ * multiple shared objects hence the need to have the mutexes as public weak
+ * symbols, in our case here, it's only used internally by liblttng-ust so we
+ * can hide them. If we end up using this compat header in another library in
+ * this project we will have to use the same scheme, but in the meantime, don't
+ * expose those symbols in the ABI.
+ */
+
+/*
+ * This comment will apply if we start using this compat header in multiple
+ * libraires.
+ *
+ * Using attribute "weak" for __lttng_ust_compat_futex_lock and
+ * __lttng_ust_compat_futex_cond. Those are globally visible by the entire
+ * program, even though many shared objects may have their own version.
+ * The first version that gets loaded will be used by the entire program
+ * (executable and all shared objects).
+ */
+
+static pthread_mutex_t __lttng_ust_compat_futex_lock = PTHREAD_MUTEX_INITIALIZER;
+static pthread_cond_t __lttng_ust_compat_futex_cond = PTHREAD_COND_INITIALIZER;
+
+/*
+ * _NOT SIGNAL-SAFE_. pthread_cond is not signal-safe anyway. Though.
+ * For now, timeout, uaddr2 and val3 are unused.
+ * Waiter will relinquish the CPU until woken up.
+ */
+
+int lttng_ust_compat_futex_noasync(int32_t *uaddr, int op, int32_t val,
+ const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
+{
+ int ret = 0, lockret;
+
+ /*
+ * Check if NULL. Don't let users expect that they are taken into
+ * account.
+ */
+ assert(!timeout);
+ assert(!uaddr2);
+ assert(!val3);
+
+ /*
+ * memory barriers to serialize with the previous uaddr modification.
+ */
+ cmm_smp_mb();
+
+ lockret = pthread_mutex_lock(&__lttng_ust_compat_futex_lock);
+ if (lockret) {
+ errno = lockret;
+ ret = -1;
+ goto end;
+ }
+ switch (op) {
+ case FUTEX_WAIT:
+ /*
+ * Wait until *uaddr is changed to something else than "val".
+ * Comparing *uaddr content against val figures out which
+ * thread has been awakened.
+ */
+ while (CMM_LOAD_SHARED(*uaddr) == val)
+ pthread_cond_wait(&__lttng_ust_compat_futex_cond,
+ &__lttng_ust_compat_futex_lock);
+ break;
+ case FUTEX_WAKE:
+ /*
+ * Each wake is sending a broadcast, thus attempting wakeup of
+ * all awaiting threads, independently of their respective
+ * uaddr.
+ */
+ pthread_cond_broadcast(&__lttng_ust_compat_futex_cond);
+ break;
+ default:
+ errno = EINVAL;
+ ret = -1;
+ }
+ lockret = pthread_mutex_unlock(&__lttng_ust_compat_futex_lock);
+ if (lockret) {
+ errno = lockret;
+ ret = -1;
+ }
+end:
+ return ret;
+}
+
+/*
+ * _ASYNC SIGNAL-SAFE_.
+ * For now, timeout, uaddr2 and val3 are unused.
+ * Waiter will busy-loop trying to read the condition.
+ * It is OK to use compat_futex_async() on a futex address on which
+ * futex() WAKE operations are also performed.
+ */
+
+int lttng_ust_compat_futex_async(int32_t *uaddr, int op, int32_t val,
+ const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
+{
+ int ret = 0;
+
+ /*
+ * Check if NULL. Don't let users expect that they are taken into
+ * account.
+ */
+ assert(!timeout);
+ assert(!uaddr2);
+ assert(!val3);
+
+ /*
+ * Ensure previous memory operations on uaddr have completed.
+ */
+ cmm_smp_mb();
+
+ switch (op) {
+ case FUTEX_WAIT:
+ while (CMM_LOAD_SHARED(*uaddr) == val) {
+ if (poll(NULL, 0, 10) < 0) {
+ ret = -1;
+ /* Keep poll errno. Caller handles EINTR. */
+ goto end;
+ }
+ }
+ break;
+ case FUTEX_WAKE:
+ break;
+ default:
+ errno = EINVAL;
+ ret = -1;
+ }
+end:
+ return ret;
+}
projects / lttng-ust.git / blobdiff