Why does load_threaded_request stay in THREAD_LOAD_IN_PROGRESS forever?

You must poll load_threaded_get_status periodically. The loader only advances when the main thread checks status. Calling load_threaded_request once and never polling leaves the load suspended. Poll every frame in _process or in a coroutine until status becomes THREAD_LOAD_LOADED.

How do I get progress from load_threaded_get_status?

Pass an Array as the second argument to load_threaded_get_status. After the call, the array's first element is fill ratio (0.0 to 1.0). Use this for a loading bar. The status itself is the return value.

Why does threaded load deadlock when loading scenes with many sub-resources?

If a sub-resource is being loaded by another threaded request, the main loader can wait on it. Avoid concurrent threaded loads of overlapping resource trees. Sequence them or use a single load for the entire tree.

Fix: Godot ResourceLoader.load_threaded_request Not Completing

Quick answer: Threaded loads only advance when the main thread polls load_threaded_get_status. Without polling, the load stays in IN_PROGRESS indefinitely. Poll every frame, watch for THREAD_LOAD_LOADED, and call load_threaded_get to retrieve the resource.

Here is how to fix Godot 4 ResourceLoader.load_threaded_request that fires off a load and never finishes. You request a heavy scene asynchronously, expecting to swap to the next level a few seconds later, and the status forever returns THREAD_LOAD_IN_PROGRESS. Threaded loading in Godot is cooperative: the loader needs the main thread to poll status to advance.

The Symptom

You call load_threaded_request("res://world.tscn") in _ready. A few frames later you call load_threaded_get_status and get IN_PROGRESS. You wait longer; still IN_PROGRESS. The CPU is mostly idle. The load never completes.

What Causes This

Status not polled. The loader uses status calls as cooperative checkpoints. Without polling, the worker thread can stall waiting for the main thread to confirm progress.

Wrong path or already-loaded resource. If the path is wrong, status returns INVALID_RESOURCE. If the resource is already in cache, the loader may complete instantly with no IN_PROGRESS phase.

Sub-resource cycle. Concurrent threaded loads of overlapping resource trees can deadlock when both try to load the same sub-resource.

Main thread starved. If _process runs heavy work (large scripts) and rarely yields, the loader has no opportunity to make progress.

The Fix

Step 1: Poll status every frame.

extends Node

var path := "res://levels/world.tscn"
var progress := []

func _ready():
    ResourceLoader.load_threaded_request(path)

func _process(_delta):
    var status = ResourceLoader.load_threaded_get_status(path, progress)
    match status:
        ResourceLoader.THREAD_LOAD_IN_PROGRESS:
            $LoadingBar.value = progress[0] * 100
        ResourceLoader.THREAD_LOAD_LOADED:
            var scene = ResourceLoader.load_threaded_get(path)
            get_tree().change_scene_to_packed(scene)
            set_process(false)
        ResourceLoader.THREAD_LOAD_FAILED:
            push_error("Load failed")
            set_process(false)

The progress array carries fill ratio in slot 0. Use it for a smooth loading bar.

Step 2: Use await for cleaner code.

func load_async(p: String) -> Resource:
    ResourceLoader.load_threaded_request(p)
    while true:
        var status = ResourceLoader.load_threaded_get_status(p)
        match status:
            ResourceLoader.THREAD_LOAD_LOADED:
                return ResourceLoader.load_threaded_get(p)
            ResourceLoader.THREAD_LOAD_FAILED, ResourceLoader.THREAD_LOAD_INVALID_RESOURCE:
                return null
        await get_tree().process_frame

Step 3: Handle invalid paths.

if not ResourceLoader.exists(path):
    push_error("Resource missing: " + path)
    return
ResourceLoader.load_threaded_request(path)

Step 4: Avoid concurrent loads of overlapping trees. If world.tscn includes player.tscn, do not threaded-load both at the same time. Load world; the world scene will pull in player as a dependency on the same load.

Step 5: Yield from heavy main-thread work. If your _process does multi-millisecond work, sprinkle await get_tree().process_frame in long loops so the threaded loader can advance status:

for i in 10000:
    do_some_work(i)
    if i % 100 == 0:
        await get_tree().process_frame

Sub-Threads And Use Sub-Threads Flag

Pass use_sub_threads = true to load_threaded_request for very large resource trees. The loader spawns sub-worker threads to load sub-resources in parallel. Beware: more parallelism does not always mean faster loads, especially for I/O-bound work on slow disks.

ResourceLoader.load_threaded_request(path, "", true)

Understanding the issue

This bug class falls into a pattern that's worth understanding beyond the specific case. In Godot Engine, the underlying behavior is shaped by how the engine layers its abstractions - the public API you call, the runtime systems that respond, and the platform-specific implementations underneath. A bug at any layer can produce symptoms that look like they originate at a different layer. Triaging effectively means recognizing which layer the symptom belongs to, even when the gameplay code is what's visible.

The specific bug described above is the kind that surfaces during integration rather than unit testing. It depends on a combination of factors: the asset configuration, the runtime state, the platform's specific behavior. In isolation, each piece looks correct; in combination, the bug emerges. This is why thorough integration testing - playing the actual game in realistic conditions - catches things that automated tests miss.

Why this happens

The triage path for this kind of bug is long. The symptom appears in gameplay, but the cause is in a different system. The reporter describes the gameplay effect; the engineer has to translate that into a hypothesis about the underlying cause. Misdirection is common.

At the engine level, the behavior comes from a deliberate design decision in Godot. The engine team chose a particular trade-off - usually performance versus convenience, or generality versus specificity - and that trade-off has consequences when you push against it. Understanding the trade-off is what turns 'this bug is mysterious' into 'this bug is the expected consequence of this design'.

Verifying the fix

After applying the fix, the verification step has three parts: confirm the original repro is resolved, confirm no obvious regressions in adjacent functionality, and (for shipping titles) deploy to a small player cohort first and watch the crash and report rates. Each step catches something the others miss.

Reproducibility is the prerequisite for verification. If you can't reliably reproduce the bug pre-fix, you can't reliably verify it post-fix. Spend time getting a clean reproduction before you write any fix code. The fix is fast once you understand the reproduction; the reproduction is the slow part.

Variations to watch for

Related bug classes often share the same root cause. If you find yourself fixing this issue, look for cousins: similar symptoms in adjacent systems, the same data flow but a different value, or the same fix pattern in another module. The catalog of 'we've seen this before' becomes valuable institutional knowledge.

Adjacent bugs often share a root cause. After fixing the case you've found, spend an hour searching the codebase for similar patterns. What's the same call with different arguments? The same data flow with a different entity type? The same lifecycle issue in a sibling system? Each match is a candidate for the same fix, or a related fix that prevents future bugs of the same class.

In production

For shipping titles with a long support window, watch for this issue resurfacing after dependency updates. Engine upgrades, driver updates, OS releases - each one can resurface a bug class you thought you'd fixed because the underlying behavior changed slightly. Regression tests catch the obvious ones; player reports catch the rest.

When triaging a similar issue in production, prioritize gathering data over hypothesizing causes. A player report describes a symptom; what you need is a build SHA, a session timestamp, and ideally a screen recording or session replay. With those, the bug becomes tractable. Without them, you're guessing at hypothetical reproductions that may not match what the player actually hit.

Performance considerations

Performance implications matter when this bug class scales with player count or asset count. A bug that fires once per session is annoying; a bug that fires once per frame compounds. After fixing, profile the affected code path under realistic load. The fix that's correct for one entity may be too slow for ten thousand.

Diagnostic approach

Before applying any fix, gather enough context to be confident you're addressing the actual cause and not a similar-looking symptom. The cheapest diagnostic step is reproducing the bug deterministically - if you can't get the same failure twice in a row, your fix attempts will be hard to evaluate. Lock down the reproduction first.

For Godot-specific diagnostics, the editor's profiler is the canonical starting point. Capture a representative frame with the symptom present; compare against a frame without the symptom; the diff often points directly at the cause. If the symptom is non-deterministic, capture multiple frames and look for the pattern - the cause is usually a state transition or a specific input value rather than a continuous effect.

Tooling and ecosystem

Third-party plugins often provide better diagnostics for their own behavior than the engine does. If the affected code is in a plugin, check the plugin's documentation for debug modes, verbose logging, or inspector tools - these can save hours of investigation when they exist.

Within Godot, the relevant diagnostic surfaces include the standard frame debugger, memory profiler, and engine-specific debug overlays. Each one shows a different facet of what's happening. The frame debugger reveals draw call ordering and state transitions; the memory profiler shows allocation patterns; the debug overlay reveals per-system state. Bugs that resist one tool usually surrender to another - the trick is knowing which tool to reach for first.

Edge cases and pitfalls

Platform-specific edge cases are worth enumerating explicitly. iOS handles backgrounding differently than Android; Windows handles focus changes differently than macOS. A fix that works on the development platform may not work on every target. Test on each shipping platform deliberately.

When writing a regression test for this fix, focus on the boundary conditions that surfaced the original bug. Tests that exercise the happy path catch obvious regressions; tests that exercise the boundary catch the subtler regressions that look like new bugs but are really the original returning. The latter are the tests that earn their keep over the long life of the project.

Team communication

When this bug class affects multiple teams (often the case for cross-system issues), early communication prevents duplicate work. The team that owns the symptom may not own the cause. A 15-minute conversation at the start of triage often saves hours of independent investigation.

If this fix touches a system several engineers work in, a short writeup in the team's engineering channel helps. Not a full design doc - a paragraph explaining what was wrong, what's fixed, and what to watch for. Future engineers encountering similar symptoms will search for the fix; making it findable is a small investment that pays back later.

“Threaded loads are cooperative. Poll status every frame, await between heavy work, and the worker advances.”

Related Issues

For Godot resource preloader issues, see Resource Preloader Not Preloading. For preload null returns, see Preload Not Finding Nested Resource.

Poll every frame. Pass progress array. Await between heavy work. Loads finish.