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fix: Improved thread usage under congestion #3258

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fix: Improved thread usage under congestion #3258

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4 changes: 4 additions & 0 deletions rclcpp/src/rclcpp/executors/events_cbg_executor/events_cbg_executor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -382,6 +382,10 @@ EventsCBGExecutor::run(
continue;
}

if(ready_entity.moreEntitiesReady) {
scheduler->unblock_one_worker_thread();
}

try {
ready_entity.entity->execute_function();
} catch (const std::exception & e) {
Expand Down
4 changes: 0 additions & 4 deletions rclcpp/src/rclcpp/executors/events_cbg_executor/first_in_first_out_scheduler.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -154,8 +154,6 @@ FirstInFirstOutScheduler::get_handle_for_callback_group(

CBGScheduler::ExecutableEntityWithInfo FirstInFirstOutScheduler::get_next_ready_entity_intern()
{
std::lock_guard l(ready_callback_groups_mutex);

while(!ready_callback_groups.empty()) {
FirstInFirstOutCallbackGroupHandle *ready_cbg =
static_cast<FirstInFirstOutCallbackGroupHandle *>(ready_callback_groups.front());
Expand Down Expand Up @@ -183,8 +181,6 @@ CBGScheduler::ExecutableEntityWithInfo FirstInFirstOutScheduler::get_next_ready_
CBGScheduler::ExecutableEntityWithInfo FirstInFirstOutScheduler::get_next_ready_entity_intern(
GlobalEventIdProvider::MonotonicId max_id)
{
std::lock_guard l(ready_callback_groups_mutex);

// as, we remove an reappend ready callback_groups during execution,
// the first ready cbg may not contain the lowest id. Therefore we
// need to search the whole deque
Expand Down
40 changes: 24 additions & 16 deletions rclcpp/src/rclcpp/executors/events_cbg_executor/scheduler.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -263,14 +263,14 @@ class CBGScheduler
*/
ExecutableEntityWithInfo get_next_ready_entity()
{
{
std::lock_guard l(ready_callback_groups_mutex);
if(needs_sync) {
needs_sync = false;
return ExecutableEntityWithInfo{.entity =
ExecutableEntity{.execute_function = sync_function, .callback_handle = nullptr},
.moreEntitiesReady = false};
}
std::lock_guard l(ready_callback_groups_mutex);
worker_checking_for_work = false;

if(needs_sync) {
needs_sync = false;
return ExecutableEntityWithInfo{.entity =
ExecutableEntity{.execute_function = sync_function, .callback_handle = nullptr},
.moreEntitiesReady = false};
}

return get_next_ready_entity_intern();
Expand All @@ -279,19 +279,22 @@ class CBGScheduler
ExecutableEntityWithInfo get_next_ready_entity(
GlobalEventIdProvider::MonotonicId max_id)
{
{
std::lock_guard l(ready_callback_groups_mutex);
if(needs_sync) {
needs_sync = false;
return ExecutableEntityWithInfo{.entity =
ExecutableEntity{.execute_function = sync_function, .callback_handle = nullptr},
.moreEntitiesReady = false};
}
std::lock_guard l(ready_callback_groups_mutex);
worker_checking_for_work = false;

if(needs_sync) {
needs_sync = false;
return ExecutableEntityWithInfo{.entity =
ExecutableEntity{.execute_function = sync_function, .callback_handle = nullptr},
.moreEntitiesReady = false};
}

return get_next_ready_entity_intern(max_id);
}

/**
* Will be called while holding the ready_callback_groups_mutex lock
*/
virtual ExecutableEntityWithInfo get_next_ready_entity_intern() = 0;
virtual ExecutableEntityWithInfo get_next_ready_entity_intern(
Comment on lines +295 to 299

@fujitatomoya fujitatomoya Sep 6, 2026

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now i do not explain why those virtual methods overload in FirstInFirstOutScheduler are public? before the PR, they were self-locking but now it is caller's responsibility as mentioned. how about moving both pure-virtual declarations into the protected: section (nothing outside the class hierarchy should call them)?

GlobalEventIdProvider::MonotonicId max_id) = 0;
Expand Down Expand Up @@ -338,6 +341,10 @@ class CBGScheduler
{
{
std::lock_guard lk(ready_callback_groups_mutex);
if(worker_checking_for_work) {
return;
}
worker_checking_for_work = true;
release_worker_once = true;
}
work_ready_conditional.notify_one();
Expand Down Expand Up @@ -385,6 +392,7 @@ class CBGScheduler

bool release_workers = false;
bool release_worker_once = false;
bool worker_checking_for_work = false;

std::condition_variable work_ready_conditional;

Expand Down