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Merge pull request #73647 from RandomShaper/fix_threaded_load 

Fix threading issues in resource loading
This commit is contained in:
Rémi Verschelde 2023-02-23 11:04:55 +01:00
parent cb9eb02788 b862fc8c9b
commit b87f9f679e
No known key found for this signature in database
GPG Key ID: C3336907360768E1
4 changed files with 156 additions and 33 deletions
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51
core/io/resource_loader.cpp
View File

@ -33,6 +33,7 @@
#include "core/config/project_settings.h"
#include "core/io/file_access.h"
#include "core/io/resource_importer.h"
#include "core/os/condition_variable.h"
#include "core/os/os.h"
#include "core/string/print_string.h"
#include "core/string/translation.h"
@ -233,7 +234,7 @@ void ResourceLoader::_thread_load_function(void *p_userdata) {
ThreadLoadTask &load_task = *(ThreadLoadTask *)p_userdata;
load_task.loader_id = Thread::get_caller_id();
if (load_task.semaphore) {
if (load_task.cond_var) {
//this is an actual thread, so wait for Ok from semaphore
thread_load_semaphore->wait(); //wait until its ok to start loading
}
@ -247,7 +248,7 @@ void ResourceLoader::_thread_load_function(void *p_userdata) {
} else {
load_task.status = THREAD_LOAD_LOADED;
}
if (load_task.semaphore) {
if (load_task.cond_var) {
if (load_task.start_next && thread_waiting_count > 0) {
thread_waiting_count--;
//thread loading count remains constant, this ends but another one begins
@ -258,11 +259,9 @@ void ResourceLoader::_thread_load_function(void *p_userdata) {
print_lt("END: load count: " + itos(thread_loading_count) + " / wait count: " + itos(thread_waiting_count) + " / suspended count: " + itos(thread_suspended_count) + " / active: " + itos(thread_loading_count - thread_suspended_count));
for (int i = 0; i < load_task.poll_requests; i++) {
load_task.semaphore->post();
}
memdelete(load_task.semaphore);
load_task.semaphore = nullptr;
load_task.cond_var->notify_all();
memdelete(load_task.cond_var);
load_task.cond_var = nullptr;
}
if (load_task.resource.is_valid()) {
@ -373,7 +372,7 @@ Error ResourceLoader::load_threaded_request(const String &p_path, const String &
if (load_task.resource.is_null()) { //needs to be loaded in thread
load_task.semaphore = memnew(Semaphore);
load_task.cond_var = memnew(ConditionVariable);
if (thread_loading_count < thread_load_max) {
thread_loading_count++;
thread_load_semaphore->post(); //we have free threads, so allow one
@ -438,9 +437,8 @@ ResourceLoader::ThreadLoadStatus ResourceLoader::load_threaded_get_status(const
Ref<Resource> ResourceLoader::load_threaded_get(const String &p_path, Error *r_error) {
String local_path = _validate_local_path(p_path);
thread_load_mutex->lock();
MutexLock thread_load_lock(*thread_load_mutex);
if (!thread_load_tasks.has(local_path)) {
thread_load_mutex->unlock();
if (r_error) {
*r_error = ERR_INVALID_PARAMETER;
}
@ -449,13 +447,21 @@ Ref<Resource> ResourceLoader::load_threaded_get(const String &p_path, Error *r_e
ThreadLoadTask &load_task = thread_load_tasks[local_path];
//semaphore still exists, meaning it's still loading, request poll
Semaphore *semaphore = load_task.semaphore;
if (semaphore) {
load_task.poll_requests++;
if (!load_task.cond_var && load_task.status == THREAD_LOAD_IN_PROGRESS) {
// A condition variable was never created for this task.
// That happens when a load has been initiated with subthreads disabled,
// but now another load thread needs to interact with this one (either
// because of subthreads being used this time, or because it's simply a
// threaded load running on a different thread).
// Since we want to be notified when the load ends, we must create the
// condition variable now.
load_task.cond_var = memnew(ConditionVariable);
}
//cond var still exists, meaning it's still loading, request poll
if (load_task.cond_var) {
{
// As we got a semaphore, this means we are going to have to wait
// As we got a cond var, this means we are going to have to wait
// until the sub-resource is done loading
//
// As this thread will become 'blocked' we should "exchange" its
@ -477,14 +483,13 @@ Ref<Resource> ResourceLoader::load_threaded_get(const String &p_path, Error *r_e
print_lt("GET: load count: " + itos(thread_loading_count) + " / wait count: " + itos(thread_waiting_count) + " / suspended count: " + itos(thread_suspended_count) + " / active: " + itos(thread_loading_count - thread_suspended_count));
}
thread_load_mutex->unlock();
semaphore->wait();
thread_load_mutex->lock();
do {
load_task.cond_var->wait(thread_load_lock);
} while (load_task.cond_var); // In case of spurious wakeup.
thread_suspended_count--;
if (!thread_load_tasks.has(local_path)) { //may have been erased during unlock and this was always an invalid call
thread_load_mutex->unlock();
if (r_error) {
*r_error = ERR_INVALID_PARAMETER;
}
@ -507,8 +512,6 @@ Ref<Resource> ResourceLoader::load_threaded_get(const String &p_path, Error *r_e
thread_load_tasks.erase(local_path);
}
thread_load_mutex->unlock();
return resource;
}
@ -1067,7 +1070,7 @@ void ResourceLoader::remove_custom_loaders() {
}
void ResourceLoader::initialize() {
thread_load_mutex = memnew(Mutex);
thread_load_mutex = memnew(SafeBinaryMutex<BINARY_MUTEX_TAG>);
thread_load_max = OS::get_singleton()->get_processor_count();
thread_loading_count = 0;
thread_waiting_count = 0;
@ -1090,7 +1093,9 @@ bool ResourceLoader::create_missing_resources_if_class_unavailable = false;
bool ResourceLoader::abort_on_missing_resource = true;
bool ResourceLoader::timestamp_on_load = false;
Mutex *ResourceLoader::thread_load_mutex = nullptr;
template <>
thread_local uint32_t SafeBinaryMutex<ResourceLoader::BINARY_MUTEX_TAG>::count = 0;
SafeBinaryMutex<ResourceLoader::BINARY_MUTEX_TAG> *ResourceLoader::thread_load_mutex = nullptr;
HashMap<String, ResourceLoader::ThreadLoadTask> ResourceLoader::thread_load_tasks;
Semaphore *ResourceLoader::thread_load_semaphore = nullptr;

9
core/io/resource_loader.h
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@ -37,6 +37,8 @@
#include "core/os/semaphore.h"
#include "core/os/thread.h"
class ConditionVariable;
class ResourceFormatLoader : public RefCounted {
GDCLASS(ResourceFormatLoader, RefCounted);
@ -105,6 +107,8 @@ public:
THREAD_LOAD_LOADED
};
static const int BINARY_MUTEX_TAG = 1;
private:
static Ref<ResourceFormatLoader> loader[MAX_LOADERS];
static int loader_count;
@ -136,7 +140,7 @@ private:
struct ThreadLoadTask {
Thread *thread = nullptr;
Thread::ID loader_id = 0;
Semaphore *semaphore = nullptr;
ConditionVariable *cond_var = nullptr;
String local_path;
String remapped_path;
String type_hint;
@ -149,12 +153,11 @@ private:
bool use_sub_threads = false;
bool start_next = true;
int requests = 0;
int poll_requests = 0;
HashSet<String> sub_tasks;
};
static void _thread_load_function(void *p_userdata);
static Mutex *thread_load_mutex;
static SafeBinaryMutex<BINARY_MUTEX_TAG> *thread_load_mutex;
static HashMap<String, ThreadLoadTask> thread_load_tasks;
static Semaphore *thread_load_semaphore;
static int thread_waiting_count;

60
core/os/condition_variable.h Normal file
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@ -0,0 +1,60 @@
/**************************************************************************/
/* condition_variable.h */
/**************************************************************************/
/* This file is part of: */
/* GODOT ENGINE */
/* https://godotengine.org */
/**************************************************************************/
/* Copyright (c) 2014-present Godot Engine contributors (see AUTHORS.md). */
/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur. */
/* */
/* Permission is hereby granted, free of charge, to any person obtaining */
/* a copy of this software and associated documentation files (the */
/* "Software"), to deal in the Software without restriction, including */
/* without limitation the rights to use, copy, modify, merge, publish, */
/* distribute, sublicense, and/or sell copies of the Software, and to */
/* permit persons to whom the Software is furnished to do so, subject to */
/* the following conditions: */
/* */
/* The above copyright notice and this permission notice shall be */
/* included in all copies or substantial portions of the Software. */
/* */
/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, */
/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF */
/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. */
/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY */
/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, */
/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE */
/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */
/**************************************************************************/
#ifndef CONDITION_VARIABLE_H
#define CONDITION_VARIABLE_H
#include <condition_variable>
// An object one or multiple threads can wait on a be notified by some other.
// Normally, you want to use a semaphore for such scenarios, but when the
// condition is something different than a count being greater than zero
// (which is the built-in logic in a semaphore) or you want to provide your
// own mutex to tie the wait-notify to some other behavior, you need to use this.
class ConditionVariable {
mutable std::condition_variable condition;
public:
template <class BinaryMutexT>
_ALWAYS_INLINE_ void wait(const MutexLock<BinaryMutexT> &p_lock) const {
condition.wait(const_cast<std::unique_lock<std::mutex> &>(p_lock.lock));
}
_ALWAYS_INLINE_ void notify_one() const {
condition.notify_one();
}
_ALWAYS_INLINE_ void notify_all() const {
condition.notify_all();
}
};
#endif // CONDITION_VARIABLE_H

69
core/os/mutex.h
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@ -31,12 +31,20 @@
#ifndef MUTEX_H
#define MUTEX_H
#include "core/error/error_macros.h"
#include "core/typedefs.h"
#include <mutex>
template <class MutexT>
class MutexLock;
template <class StdMutexT>
class MutexImpl {
friend class MutexLock<MutexImpl<StdMutexT>>;
using StdMutexType = StdMutexT;
mutable StdMutexT mutex;
public:
@ -53,18 +61,65 @@ public:
}
};
// A very special kind of mutex, used in scenarios where these
// requirements hold at the same time:
// - Must be used with a condition variable (only binary mutexes are suitable).
// - Must have recursive semnantics (or simulate, as this one does).
// The implementation keeps the lock count in TS. Therefore, only
// one object of each version of the template can exists; hence the Tag argument.
// Tags must be unique across the Godot codebase.
// Also, don't forget to declare the thread_local variable on each use.
template <int Tag>
class SafeBinaryMutex {
friend class MutexLock<SafeBinaryMutex>;
using StdMutexType = std::mutex;
mutable std::mutex mutex;
static thread_local uint32_t count;
public:
_ALWAYS_INLINE_ void lock() const {
if (++count == 1) {
mutex.lock();
}
}
_ALWAYS_INLINE_ void unlock() const {
DEV_ASSERT(count);
if (--count == 0) {
mutex.unlock();
}
}
_ALWAYS_INLINE_ bool try_lock() const {
if (count) {
count++;
return true;
} else {
if (mutex.try_lock()) {
count++;
return true;
} else {
return false;
}
}
}
~SafeBinaryMutex() {
DEV_ASSERT(!count);
}
};
template <class MutexT>
class MutexLock {
const MutexT &mutex;
friend class ConditionVariable;
std::unique_lock<typename MutexT::StdMutexType> lock;
public:
_ALWAYS_INLINE_ explicit MutexLock(const MutexT &p_mutex) :
mutex(p_mutex) {
mutex.lock();
}
_ALWAYS_INLINE_ ~MutexLock() {
mutex.unlock();
lock(p_mutex.mutex) {
}
};