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Fixup recent changes to threading concerns

Browse source 
ResourceLoader:
- Fix invalid tokens being returned.
- Remove no longer written `ThreadLoadTask::dependent_path` and the code reading from it.
- Clear deadlock hazard by keeping the mutex unlocked during userland polling.

WorkerThreadPool:
- Include thread call queue override in the thread state reset set, which allows to simplify the code that handled that (imperfectly) in the ResourceLoader.
- Handle the mutex type correctly on entering an allowance zone.

CommandQueueMT:
- Handle the additional possibility of command buffer reallocation that mutex unlock allowance introduces.
This commit is contained in:
Pedro J. Estébanez 2024-07-09 18:41:24 +02:00
parent 10b543f8a7
commit 5b5cdf2414
4 changed files with 53 additions and 49 deletions
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88
core/io/resource_loader.cpp
View file

@ -304,31 +304,23 @@ void ResourceLoader::_thread_load_function(void *p_userdata) {
thread_load_mutex.unlock();
// Thread-safe either if it's the current thread or a brand new one.
thread_local bool mq_override_present = false;
CallQueue *own_mq_override = nullptr;
if (load_nesting == 0) {
mq_override_present = false;
load_paths_stack = memnew(Vector<String>);
if (!load_task.dependent_path.is_empty()) {
load_paths_stack->push_back(load_task.dependent_path);
}
if (!Thread::is_main_thread()) {
// Let the caller thread use its own, for added flexibility. Provide one otherwise.
if (MessageQueue::get_singleton() == MessageQueue::get_main_singleton()) {
own_mq_override = memnew(CallQueue);
MessageQueue::set_thread_singleton_override(own_mq_override);
}
mq_override_present = true;
set_current_thread_safe_for_nodes(true);
}
} else {
DEV_ASSERT(load_task.dependent_path.is_empty());
}
// --
Ref<Resource> res = _load(load_task.remapped_path, load_task.remapped_path != load_task.local_path ? load_task.local_path : String(), load_task.type_hint, load_task.cache_mode, &load_task.error, load_task.use_sub_threads, &load_task.progress);
if (mq_override_present) {
if (MessageQueue::get_singleton() != MessageQueue::get_main_singleton()) {
MessageQueue::get_singleton()->flush();
}
@ -473,12 +465,13 @@ Ref<ResourceLoader::LoadToken> ResourceLoader::_load_start(const String &p_path,
if (!ignoring_cache && thread_load_tasks.has(local_path)) {
load_token = Ref<LoadToken>(thread_load_tasks[local_path].load_token);
if (!load_token.is_valid()) {
if (load_token.is_valid()) {
return load_token;
} else {
// The token is dying (reached 0 on another thread).
// Ensure it's killed now so the path can be safely reused right away.
thread_load_tasks[local_path].load_token->clear();
}
return load_token;
}
load_token.instantiate();
@ -560,37 +553,44 @@ float ResourceLoader::_dependency_get_progress(const String &p_path) {
}
ResourceLoader::ThreadLoadStatus ResourceLoader::load_threaded_get_status(const String &p_path, float *r_progress) {
MutexLock thread_load_lock(thread_load_mutex);
bool ensure_progress = false;
ThreadLoadStatus status = THREAD_LOAD_IN_PROGRESS;
{
MutexLock thread_load_lock(thread_load_mutex);
if (!user_load_tokens.has(p_path)) {
print_verbose("load_threaded_get_status(): No threaded load for resource path '" + p_path + "' has been initiated or its result has already been collected.");
return THREAD_LOAD_INVALID_RESOURCE;
}
String local_path = _validate_local_path(p_path);
if (!thread_load_tasks.has(local_path)) {
#ifdef DEV_ENABLED
CRASH_NOW();
#endif
// On non-dev, be defensive and at least avoid crashing (at this point at least).
return THREAD_LOAD_INVALID_RESOURCE;
}
ThreadLoadTask &load_task = thread_load_tasks[local_path];
ThreadLoadStatus status;
status = load_task.status;
if (r_progress) {
*r_progress = _dependency_get_progress(local_path);
}
// Support userland polling in a loop on the main thread.
if (Thread::is_main_thread() && status == THREAD_LOAD_IN_PROGRESS) {
uint64_t frame = Engine::get_singleton()->get_process_frames();
if (frame == load_task.last_progress_check_main_thread_frame) {
_ensure_load_progress();
} else {
load_task.last_progress_check_main_thread_frame = frame;
if (!user_load_tokens.has(p_path)) {
print_verbose("load_threaded_get_status(): No threaded load for resource path '" + p_path + "' has been initiated or its result has already been collected.");
return THREAD_LOAD_INVALID_RESOURCE;
}
String local_path = _validate_local_path(p_path);
if (!thread_load_tasks.has(local_path)) {
#ifdef DEV_ENABLED
CRASH_NOW();
#endif
// On non-dev, be defensive and at least avoid crashing (at this point at least).
return THREAD_LOAD_INVALID_RESOURCE;
}
ThreadLoadTask &load_task = thread_load_tasks[local_path];
status = load_task.status;
if (r_progress) {
*r_progress = _dependency_get_progress(local_path);
}
// Support userland polling in a loop on the main thread.
if (Thread::is_main_thread() && status == THREAD_LOAD_IN_PROGRESS) {
uint64_t frame = Engine::get_singleton()->get_process_frames();
if (frame == load_task.last_progress_check_main_thread_frame) {
ensure_progress = true;
} else {
load_task.last_progress_check_main_thread_frame = frame;
}
}
}
if (ensure_progress) {
_ensure_load_progress();
}
return status;
@ -626,13 +626,13 @@ Ref<Resource> ResourceLoader::load_threaded_get(const String &p_path, Error *r_e
if (Thread::is_main_thread() && !load_token->local_path.is_empty()) {
const ThreadLoadTask &load_task = thread_load_tasks[load_token->local_path];
while (load_task.status == THREAD_LOAD_IN_PROGRESS) {
if (!_ensure_load_progress()) {
// This local poll loop is not needed.
break;
}
thread_load_lock.~MutexLock();
bool exit = !_ensure_load_progress();
OS::get_singleton()->delay_usec(1000);
new (&thread_load_lock) MutexLock(thread_load_mutex);
if (exit) {
break;
}
}
}

1
core/io/resource_loader.h
View file

@ -170,7 +170,6 @@ private:
LoadToken *load_token = nullptr;
String local_path;
String remapped_path;
String dependent_path;
String type_hint;
float progress = 0.0f;
float max_reported_progress = 0.0f;

5
core/object/worker_thread_pool.cpp
View file

@ -59,8 +59,9 @@ void WorkerThreadPool::_process_task(Task *p_task) {
CallQueue *call_queue_backup = MessageQueue::get_singleton() != MessageQueue::get_main_singleton() ? MessageQueue::get_singleton() : nullptr;
{
// Tasks must start with this unset. They are free to set-and-forget otherwise.
// Tasks must start with these at default values. They are free to set-and-forget otherwise.
set_current_thread_safe_for_nodes(false);
MessageQueue::set_thread_singleton_override(nullptr);
// Since the WorkerThreadPool is started before the script server,
// its pre-created threads can't have ScriptServer::thread_enter() called on them early.
// Therefore, we do it late at the first opportunity, so in case the task
@ -671,7 +672,7 @@ uint32_t WorkerThreadPool::thread_enter_unlock_allowance_zone(BinaryMutex *p_mut
uint32_t WorkerThreadPool::_thread_enter_unlock_allowance_zone(void *p_mutex, bool p_is_binary) {
for (uint32_t i = 0; i < MAX_UNLOCKABLE_MUTEXES; i++) {
if (unlikely(unlockable_mutexes[i] == (uintptr_t)p_mutex)) {
if (unlikely((unlockable_mutexes[i] & ~1) == (uintptr_t)p_mutex)) {
// Already registered in the current thread.
return UINT32_MAX;
}

8
core/templates/command_queue_mt.h
View file

@ -370,15 +370,19 @@ class CommandQueueMT {
flush_read_ptr += 8;
CommandBase *cmd = reinterpret_cast<CommandBase *>(&command_mem[flush_read_ptr]);
cmd->call();
// Handle potential realloc due to the command and unlock allowance.
cmd = reinterpret_cast<CommandBase *>(&command_mem[flush_read_ptr]);
if (unlikely(cmd->sync)) {
sync_head++;
unlock(); // Give an opportunity to awaiters right away.
sync_cond_var.notify_all();
lock();
// Handle potential realloc happened during unlock.
cmd = reinterpret_cast<CommandBase *>(&command_mem[flush_read_ptr]);
}
// If the command involved reallocating the buffer, the address may have changed.
cmd = reinterpret_cast<CommandBase *>(&command_mem[flush_read_ptr]);
cmd->~CommandBase();
flush_read_ptr += size;