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ResourceLoader: Support polling and get-before-complete on the main thread #93695

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merged 1 commit into from
Jun 28, 2024
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ResourceLoader: Support polling and get-before-complete on the main thread #93695

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37 changes: 37 additions & 0 deletions core/io/resource_loader.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,7 @@
#include "core/string/print_string.h"
#include "core/string/translation.h"
#include "core/variant/variant_parser.h"
#include "servers/rendering_server.h"

#ifdef DEBUG_LOAD_THREADED
#define print_lt(m_text) print_line(m_text)
Expand Down Expand Up @@ -585,6 +586,16 @@ ResourceLoader::ThreadLoadStatus ResourceLoader::load_threaded_get_status(const
*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;
}
}

return status;
}

Expand Down Expand Up @@ -613,6 +624,21 @@ Ref<Resource> ResourceLoader::load_threaded_get(const String &p_path, Error *r_e
}
return Ref<Resource>();
}

// Support userland requesting on the main thread before the load is reported to be complete.
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();
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This makes me think a branch I made some time ago to allow unlocking and re-locking of MutexLock is needed, it was just a hypothetical idea then but will revive it and open a PR if it works well still, to avoid potentially hacky solutions

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Good point, but I think this may not be really a good thing to do depending on the kind of mutex now we have #93701. I haven't checked it yet, but I'm suspicious of this.

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The issue was something else in the end.

OS::get_singleton()->delay_usec(1000);
new (&thread_load_lock) MutexLock(thread_load_mutex);
}
}

res = _load_complete_inner(*load_token, r_error, thread_load_lock);
if (load_token->unreference()) {
memdelete(load_token);
Expand Down Expand Up @@ -731,6 +757,17 @@ Ref<Resource> ResourceLoader::_load_complete_inner(LoadToken &p_load_token, Erro
}
}

bool ResourceLoader::_ensure_load_progress() {
// Some servers may need a new engine iteration to allow the load to progress.
// Since the only known one is the rendering server (in single thread mode), let's keep it simple and just sync it.
// This may be refactored in the future to support other servers and have less coupling.
if (OS::get_singleton()->get_render_thread_mode() == OS::RENDER_SEPARATE_THREAD) {
return false; // Not needed.
}
RenderingServer::get_singleton()->sync();
return true;
}

Ref<Resource> ResourceLoader::ensure_resource_ref_override_for_outer_load(const String &p_path, const String &p_res_type) {
ERR_FAIL_COND_V(load_nesting == 0, Ref<Resource>()); // It makes no sense to use this from nesting level 0.
const String &local_path = _validate_local_path(p_path);
Expand Down
3 changes: 3 additions & 0 deletions core/io/resource_loader.h
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Original file line number Diff line number Diff line change
Expand Up @@ -174,6 +174,7 @@ class ResourceLoader {
String type_hint;
float progress = 0.0f;
float max_reported_progress = 0.0f;
uint64_t last_progress_check_main_thread_frame = UINT64_MAX;
ThreadLoadStatus status = THREAD_LOAD_IN_PROGRESS;
ResourceFormatLoader::CacheMode cache_mode = ResourceFormatLoader::CACHE_MODE_REUSE;
Error error = OK;
Expand All @@ -197,6 +198,8 @@ class ResourceLoader {

static float _dependency_get_progress(const String &p_path);

static bool _ensure_load_progress();

public:
static Error load_threaded_request(const String &p_path, const String &p_type_hint = "", bool p_use_sub_threads = false, ResourceFormatLoader::CacheMode p_cache_mode = ResourceFormatLoader::CACHE_MODE_REUSE);
static ThreadLoadStatus load_threaded_get_status(const String &p_path, float *r_progress = nullptr);
Expand Down
3 changes: 2 additions & 1 deletion doc/classes/ResourceLoader.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -87,7 +87,7 @@
<param index="0" name="path" type="String" />
<description>
Returns the resource loaded by [method load_threaded_request].
If this is called before the loading thread is done (i.e. [method load_threaded_get_status] is not [constant THREAD_LOAD_LOADED]), the calling thread will be blocked until the resource has finished loading.
If this is called before the loading thread is done (i.e. [method load_threaded_get_status] is not [constant THREAD_LOAD_LOADED]), the calling thread will be blocked until the resource has finished loading. However, it's recommended to use [method load_threaded_get_status] to known when the load has actually completed.
</description>
</method>
<method name="load_threaded_get_status">
Expand All @@ -97,6 +97,7 @@
<description>
Returns the status of a threaded loading operation started with [method load_threaded_request] for the resource at [param path]. See [enum ThreadLoadStatus] for possible return values.
An array variable can optionally be passed via [param progress], and will return a one-element array containing the percentage of completion of the threaded loading.
[b]Note:[/b] The recommended way of using this method is to call it during different frames (e.g., in [method Node._process], instead of a loop).
</description>
</method>
<method name="load_threaded_request">
Expand Down
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