*
*/
-#include "waiter.hpp"
-#include <urcu/uatomic.h>
-#include <urcu/futex.h>
#include "error.hpp"
+#include "macros.hpp"
+#include "waiter.hpp"
+
#include <poll.h>
+#include <urcu/futex.h>
+#include <urcu/uatomic.h>
-/*
- * Number of busy-loop attempts before waiting on futex.
- */
-#define WAIT_ATTEMPTS 1000
+namespace {
+/* Number of busy-loop attempts before waiting on futex. */
+constexpr auto wait_attempt_count = 1000;
enum waiter_state {
/* WAITER_WAITING is compared directly (futex compares it). */
- WAITER_WAITING = 0,
+ WAITER_WAITING = 0,
/* non-zero are used as masks. */
- WAITER_WOKEN_UP = (1 << 0),
- WAITER_RUNNING = (1 << 1),
- WAITER_TEARDOWN = (1 << 2),
+ WAITER_WOKEN_UP = (1 << 0),
+ WAITER_RUNNING = (1 << 1),
+ WAITER_TEARDOWN = (1 << 2),
};
+} /* namespace */
+
+lttng::synchro::waiter::waiter()
+{
+ arm();
+}
-void lttng_waiter_init(struct lttng_waiter *waiter)
+void lttng::synchro::waiter::arm() noexcept
{
- cds_wfs_node_init(&waiter->wait_queue_node);
- uatomic_set(&waiter->state, WAITER_WAITING);
+ cds_wfs_node_init(&_wait_queue_node);
+ uatomic_set(&_state, WAITER_WAITING);
cmm_smp_mb();
}
/*
- * User must init "waiter" before passing its memory to waker thread.
+ * User must arm "waiter" before passing its memory to waker thread.
*/
-void lttng_waiter_wait(struct lttng_waiter *waiter)
+void lttng::synchro::waiter::wait()
{
- unsigned int i;
+ DBG("Beginning of waiter \"wait\" period");
- DBG("Beginning of waiter wait period");
- /* Load and test condition before read state */
+ /* Load and test condition before read state. */
cmm_smp_rmb();
- for (i = 0; i < WAIT_ATTEMPTS; i++) {
- if (uatomic_read(&waiter->state) != WAITER_WAITING) {
+ for (unsigned int i = 0; i < wait_attempt_count; i++) {
+ if (uatomic_read(&_state) != WAITER_WAITING) {
goto skip_futex_wait;
}
+
caa_cpu_relax();
}
- while (futex_noasync(&waiter->state, FUTEX_WAIT, WAITER_WAITING,
- NULL, NULL, 0)) {
+
+ while (uatomic_read(&_state) == WAITER_WAITING) {
+ if (!futex_noasync(&_state, FUTEX_WAIT, WAITER_WAITING, nullptr, nullptr, 0)) {
+ /*
+ * Prior queued wakeups queued by unrelated code
+ * using the same address can cause futex wait to
+ * return 0 even through the futex value is still
+ * WAITER_WAITING (spurious wakeups). Check
+ * the value again in user-space to validate
+ * whether it really differs from WAITER_WAITING.
+ */
+ continue;
+ }
+
switch (errno) {
- case EWOULDBLOCK:
+ case EAGAIN:
/* Value already changed. */
goto skip_futex_wait;
case EINTR:
/* Retry if interrupted by signal. */
- break; /* Get out of switch. */
+ break; /* Get out of switch. Check again. */
default:
/* Unexpected error. */
PERROR("futex_noasync");
skip_futex_wait:
/* Tell waker thread than we are running. */
- uatomic_or(&waiter->state, WAITER_RUNNING);
+ uatomic_or(&_state, WAITER_RUNNING);
/*
* Wait until waker thread lets us know it's ok to tear down
* memory allocated for struct lttng_waiter.
*/
- for (i = 0; i < WAIT_ATTEMPTS; i++) {
- if (uatomic_read(&waiter->state) & WAITER_TEARDOWN) {
+ for (unsigned int i = 0; i < wait_attempt_count; i++) {
+ if (uatomic_read(&_state) & WAITER_TEARDOWN) {
break;
}
+
caa_cpu_relax();
}
- while (!(uatomic_read(&waiter->state) & WAITER_TEARDOWN)) {
- poll(NULL, 0, 10);
+
+ while (!(uatomic_read(&_state) & WAITER_TEARDOWN)) {
+ poll(nullptr, 0, 10);
}
- LTTNG_ASSERT(uatomic_read(&waiter->state) & WAITER_TEARDOWN);
- DBG("End of waiter wait period");
+
+ LTTNG_ASSERT(uatomic_read(&_state) & WAITER_TEARDOWN);
+ DBG("End of waiter \"wait\" period");
+}
+
+lttng::synchro::waker lttng::synchro::waiter::get_waker()
+{
+ return lttng::synchro::waker(_state);
}
/*
* execution. In this scheme, the waiter owns the node memory, and we only allow
* it to free this memory when it sees the WAITER_TEARDOWN flag.
*/
-void lttng_waiter_wake_up(struct lttng_waiter *waiter)
+void lttng::synchro::waker::wake()
{
cmm_smp_mb();
- LTTNG_ASSERT(uatomic_read(&waiter->state) == WAITER_WAITING);
- uatomic_set(&waiter->state, WAITER_WOKEN_UP);
- if (!(uatomic_read(&waiter->state) & WAITER_RUNNING)) {
- if (futex_noasync(&waiter->state, FUTEX_WAKE, 1,
- NULL, NULL, 0) < 0) {
+
+ LTTNG_ASSERT(uatomic_read(&_state.get()) == WAITER_WAITING);
+
+ uatomic_set(&_state.get(), WAITER_WOKEN_UP);
+ if (!(uatomic_read(&_state.get()) & WAITER_RUNNING)) {
+ if (futex_noasync(&_state.get(), FUTEX_WAKE, 1, nullptr, nullptr, 0) < 0) {
PERROR("futex_noasync");
abort();
}
}
+
/* Allow teardown of struct urcu_wait memory. */
- uatomic_or(&waiter->state, WAITER_TEARDOWN);
+ uatomic_or(&_state.get(), WAITER_TEARDOWN);
+}
+
+lttng::synchro::wait_queue::wait_queue()
+{
+ cds_wfs_init(&_stack);
+}
+
+void lttng::synchro::wait_queue::add(waiter& waiter) noexcept
+{
+ (void) cds_wfs_push(&_stack, &waiter._wait_queue_node);
+}
+
+void lttng::synchro::wait_queue::wake_all()
+{
+ /* Move all waiters from the queue to our local stack. */
+ auto *waiters = __cds_wfs_pop_all(&_stack);
+
+ /* Wake all waiters in our stack head. */
+ cds_wfs_node *iter, *iter_n;
+ cds_wfs_for_each_blocking_safe (waiters, iter, iter_n) {
+ auto& waiter = *lttng::utils::container_of(
+ iter, <tng::synchro::waiter::_wait_queue_node);
+
+ /* Don't wake already running threads. */
+ if (waiter._state & WAITER_RUNNING) {
+ continue;
+ }
+
+ waiter.get_waker().wake();
+ }
}
projects / lttng-tools.git / blobdiff