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improved rcl_wait in the area of timeout computation and spurious wak…
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…eups (#1146)

Added special handling for timers with a clock that has time override
enabled. For these timer we should not compute a timeout, as the waitset
is waken up by the associated guard condition.
Before this change, the waitset could wait up, because of an expected ready
timer, that was acutally not ready, as the time update to the ROS_TIME had
not yet arrived.

Signed-off-by: Janosch Machowinski <[email protected]>
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@jmachowinski
jmachowinski authored Apr 3, 2024
1 parent b7ed9ab commit db366ac
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Showing 4 changed files with 285 additions and 30 deletions.
26 changes: 25 additions & 1 deletion rcl/include/rcl/timer.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -319,7 +319,7 @@ rcl_timer_call_with_info(rcl_timer_t * timer, rcl_timer_call_info_t * call_info)
RCL_PUBLIC
RCL_WARN_UNUSED
rcl_ret_t
rcl_timer_clock(rcl_timer_t * timer, rcl_clock_t ** clock);
rcl_timer_clock(const rcl_timer_t * timer, rcl_clock_t ** clock);

/// Calculates whether or not the timer should be called.
/**
Expand Down Expand Up @@ -387,6 +387,30 @@ RCL_WARN_UNUSED
rcl_ret_t
rcl_timer_get_time_until_next_call(const rcl_timer_t * timer, int64_t * time_until_next_call);

/// Retrieve the time when the next call to rcl_timer_call() shall occur.
/**
* <hr>
* Attribute | Adherence
* ------------------ | -------------
* Allocates Memory | No
* Thread-Safe | Yes
* Uses Atomics | Yes
* Lock-Free | Yes [1]
* <i>[1] if `atomic_is_lock_free()` returns true for `atomic_int_least64_t`</i>
*
* \param[in] timer the handle to the timer that is being queried
* \param[out] next_call_time the output variable for the result
* \return #RCL_RET_OK if the timer until next call was successfully calculated, or
* \return #RCL_RET_INVALID_ARGUMENT if any arguments are invalid, or
* \return #RCL_RET_TIMER_INVALID if the timer->impl is invalid, or
* \return #RCL_RET_TIMER_CANCELED if the timer is canceled, or
* \return #RCL_RET_ERROR an unspecified error occur.
*/
RCL_PUBLIC
RCL_WARN_UNUSED
rcl_ret_t
rcl_timer_get_next_call_time(const rcl_timer_t * timer, int64_t * next_call_time);

/// Retrieve the time since the previous call to rcl_timer_call() occurred.
/**
* This function calculates the time since the last call and copies it into
Expand Down
18 changes: 17 additions & 1 deletion rcl/src/rcl/timer.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -254,7 +254,7 @@ rcl_timer_fini(rcl_timer_t * timer)
RCL_PUBLIC
RCL_WARN_UNUSED
rcl_ret_t
rcl_timer_clock(rcl_timer_t * timer, rcl_clock_t ** clock)
rcl_timer_clock(const rcl_timer_t * timer, rcl_clock_t ** clock)
{
RCL_CHECK_ARGUMENT_FOR_NULL(timer, RCL_RET_INVALID_ARGUMENT);
RCL_CHECK_ARGUMENT_FOR_NULL(clock, RCL_RET_INVALID_ARGUMENT);
Expand Down Expand Up @@ -343,6 +343,22 @@ rcl_timer_is_ready(const rcl_timer_t * timer, bool * is_ready)
return RCL_RET_OK;
}

rcl_ret_t
rcl_timer_get_next_call_time(const rcl_timer_t * timer, int64_t * next_call_time)
{
RCL_CHECK_ARGUMENT_FOR_NULL(timer, RCL_RET_INVALID_ARGUMENT);
RCL_CHECK_ARGUMENT_FOR_NULL(timer->impl, RCL_RET_TIMER_INVALID);
RCL_CHECK_ARGUMENT_FOR_NULL(next_call_time, RCL_RET_INVALID_ARGUMENT);

if (rcutils_atomic_load_bool(&timer->impl->canceled)) {
return RCL_RET_TIMER_CANCELED;
}

*next_call_time =
rcutils_atomic_load_int64_t(&timer->impl->next_call_time);
return RCL_RET_OK;
}

rcl_ret_t
rcl_timer_get_time_until_next_call(const rcl_timer_t * timer, int64_t * time_until_next_call)
{
Expand Down
130 changes: 102 additions & 28 deletions rcl/src/rcl/wait.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -541,54 +541,123 @@ rcl_wait(rcl_wait_set_t * wait_set, int64_t timeout)
// By default, set the timer to block indefinitely if none of the below conditions are met.
rmw_time_t * timeout_argument = NULL;
rmw_time_t temporary_timeout_storage;
bool is_non_blocking = timeout == 0;

bool is_timer_timeout = false;
int64_t min_timeout = timeout > 0 ? timeout : INT64_MAX;
{ // scope to prevent i from colliding below
uint64_t i = 0;
for (i = 0; i < wait_set->impl->timer_index; ++i) {
if (!wait_set->timers[i]) {
for (uint64_t t_idx = 0; t_idx < wait_set->impl->timer_index; ++t_idx) {
if (!wait_set->timers[t_idx]) {
continue; // Skip NULL timers.
}
rmw_guard_conditions_t * rmw_gcs = &(wait_set->impl->rmw_guard_conditions);
size_t gc_idx = wait_set->size_of_guard_conditions + t_idx;
if (NULL != rmw_gcs->guard_conditions[gc_idx]) {
// This timer has a guard condition, so move it to make a legal wait set.
rmw_gcs->guard_conditions[rmw_gcs->guard_condition_count] =
rmw_gcs->guard_conditions[gc_idx];
++(rmw_gcs->guard_condition_count);
}
}

int64_t min_next_call_time[RCL_STEADY_TIME + 1];
rcl_clock_t * clocks[RCL_STEADY_TIME + 1] = {0, 0, 0, 0};

min_next_call_time[RCL_ROS_TIME] = INT64_MAX;
min_next_call_time[RCL_SYSTEM_TIME] = INT64_MAX;
min_next_call_time[RCL_STEADY_TIME] = INT64_MAX;

if (!is_non_blocking) {
for (size_t t_idx = 0; t_idx < wait_set->impl->timer_index; ++t_idx) {
if (!wait_set->timers[t_idx]) {
continue; // Skip NULL timers.
}
rmw_guard_conditions_t * rmw_gcs = &(wait_set->impl->rmw_guard_conditions);
size_t gc_idx = wait_set->size_of_guard_conditions + i;
if (NULL != rmw_gcs->guard_conditions[gc_idx]) {
// This timer has a guard condition, so move it to make a legal wait set.
rmw_gcs->guard_conditions[rmw_gcs->guard_condition_count] =
rmw_gcs->guard_conditions[gc_idx];
++(rmw_gcs->guard_condition_count);

rcl_clock_t * clock;
if (rcl_timer_clock(wait_set->timers[t_idx], &clock) != RCL_RET_OK) {
// should never happen
return RCL_RET_ERROR;
}
// use timer time to to set the rmw_wait timeout
// TODO(sloretz) fix spurious wake-ups on ROS_TIME timers with ROS_TIME enabled
int64_t timer_timeout = INT64_MAX;
rcl_ret_t ret = rcl_timer_get_time_until_next_call(wait_set->timers[i], &timer_timeout);

if (clock->type == RCL_ROS_TIME) {
bool timer_override_active = false;
if (rcl_is_enabled_ros_time_override(clock, &timer_override_active) != RCL_RET_OK) {
// should never happen
return RCL_RET_ERROR;
}

if (timer_override_active) {
// we need to check, it the timer is already ready
bool override_timer_is_ready = false;
if (rcl_timer_is_ready(wait_set->timers[t_idx], &override_timer_is_ready) != RCL_RET_OK) {
// should never happen
return RCL_RET_ERROR;
}

if (override_timer_is_ready) {
// no need to search further for the timeout, we need to wake up instantly
is_non_blocking = true;
break;
}

// if the timer override is active, there is no point in computing a wait time,
// as it might be on a total wrong time basis. In case this timer becomes ready,
// the guard_condition above will wake us.
continue;
}
}

// get the time of the next call to the timer
int64_t next_call_time = INT64_MAX;
rcl_ret_t ret = rcl_timer_get_next_call_time(wait_set->timers[t_idx], &next_call_time);
if (ret == RCL_RET_TIMER_CANCELED) {
wait_set->timers[i] = NULL;
wait_set->timers[t_idx] = NULL;
continue;
}
if (ret != RCL_RET_OK) {
return ret; // The rcl error state should already be set.
}
if (timer_timeout < min_timeout) {
is_timer_timeout = true;
min_timeout = timer_timeout;
if (next_call_time < min_next_call_time[clock->type]) {
clocks[clock->type] = clock;
min_next_call_time[clock->type] = next_call_time;
}
}
}

if (timeout == 0) {
// Then it is non-blocking, so set the temporary storage to 0, 0 and pass it.
if (is_non_blocking) {
temporary_timeout_storage.sec = 0;
temporary_timeout_storage.nsec = 0;
timeout_argument = &temporary_timeout_storage;
} else if (timeout > 0 || is_timer_timeout) {
} else {
int64_t min_timeout = timeout > 0 ? timeout : INT64_MAX;
bool has_valid_timeout = timeout > 0;

// determine the min timeout of all clocks
for (size_t i = RCL_ROS_TIME; i <= RCL_STEADY_TIME; i++) {
if (clocks[i] == 0) {
continue;
}

int64_t cur_time;
rmw_ret_t ret = rcl_clock_get_now(clocks[i], &cur_time);
if (ret != RCL_RET_OK) {
return ret; // The rcl error state should already be set.
}

int64_t timer_timeout = min_next_call_time[i] - cur_time;

if (timer_timeout <= min_timeout) {
has_valid_timeout = true;
min_timeout = timer_timeout;
}
}

// If min_timeout was negative, we need to wake up immediately.
if (min_timeout < 0) {
min_timeout = 0;
}
temporary_timeout_storage.sec = RCL_NS_TO_S(min_timeout);
temporary_timeout_storage.nsec = min_timeout % 1000000000;
timeout_argument = &temporary_timeout_storage;
if (has_valid_timeout) {
temporary_timeout_storage.sec = RCL_NS_TO_S(min_timeout);
temporary_timeout_storage.nsec = min_timeout % 1000000000;
timeout_argument = &temporary_timeout_storage;
}
}

// Wait.
Expand All @@ -604,20 +673,25 @@ rcl_wait(rcl_wait_set_t * wait_set, int64_t timeout)
// Items that are not ready will have been set to NULL by rmw_wait.
// We now update our handles accordingly.

bool timer_is_ready = false;

// Check for ready timers
// and set not ready timers (which includes canceled timers) to NULL.
size_t i;
for (i = 0; i < wait_set->impl->timer_index; ++i) {
if (!wait_set->timers[i]) {
continue;
}

bool is_ready = false;
rcl_ret_t ret = rcl_timer_is_ready(wait_set->timers[i], &is_ready);
if (ret != RCL_RET_OK) {
return ret; // The rcl error state should already be set.
}
if (!is_ready) {
wait_set->timers[i] = NULL;
} else {
timer_is_ready = true;
}
}
// Check for timeout, return RCL_RET_TIMEOUT only if it wasn't a timer.
Expand Down Expand Up @@ -661,7 +735,7 @@ rcl_wait(rcl_wait_set_t * wait_set, int64_t timeout)
}
}

if (RMW_RET_TIMEOUT == ret && !is_timer_timeout) {
if (RMW_RET_TIMEOUT == ret && !timer_is_ready) {
return RCL_RET_TIMEOUT;
}
return RCL_RET_OK;
Expand Down
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