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Merged
leehack merged 2 commits into from
May 8, 2026
Merged

fix(webgpu): stabilize qwen streaming and multimodal fallback #4

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a92936f
fix(webgpu): stabilize qwen streaming and multimodal fallback
leehack Mar 8, 2026
ab7ad67
fix(webgpu): narrow multimodal CPU fallback
leehack May 8, 2026
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142 changes: 113 additions & 29 deletions js/llama_webgpu_bridge.js
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Original file line number Diff line number Diff line change
Expand Up @@ -549,6 +549,26 @@ function toUint8Array(value) {
return null;
}

function trimUnstableUtf8Tail(text) {
if (typeof text !== 'string' || text.length === 0) {
return '';
}

let end = text.length;
while (end > 0 && text.charCodeAt(end - 1) === 0xFFFD) {
end -= 1;
}

if (end > 0) {
const tail = text.charCodeAt(end - 1);
if (tail >= 0xD800 && tail <= 0xDBFF) {
end -= 1;
}
}

return end === text.length ? text : text.slice(0, end);
}

function toFloat32Array(value) {
if (!value) {
return null;
Expand Down Expand Up @@ -3831,7 +3851,8 @@ class LlamaWebGpuBridgeRuntime {
const shouldYieldForResponsiveness =
!(typeof WorkerGlobalScope !== 'undefined' && globalThis instanceof WorkerGlobalScope);
const yieldInterval = shouldYieldForResponsiveness ? 4 : 0;
let streamed = shouldEmitCurrentText ? '' : null;
let streamed = '';
let emittedStableText = '';

while (generated < nPredict) {
if (this._abortRequested || options.signal?.aborted) {
Expand Down Expand Up @@ -3888,19 +3909,25 @@ class LlamaWebGpuBridgeRuntime {
}

generated += 1;
const piece = this._core.ccall('llamadart_webgpu_last_piece', 'string', [], []) || '';
if (piece.length === 0) {
const fullText = this._core.ccall('llamadart_webgpu_last_output', 'string', [], []) || '';
streamed = fullText;
const stableText = trimUnstableUtf8Tail(fullText);

if (!stableText.startsWith(emittedStableText)) {
emittedStableText = '';
}

const deltaText = stableText.slice(emittedStableText.length);
if (deltaText.length === 0) {
continue;
}
emittedStableText = stableText;

if (typeof options.onToken === 'function') {
const piecePayload = emitTokenText ? piece : textEncoder.encode(piece);
if (shouldEmitCurrentText) {
streamed += piece;
options.onToken(piecePayload, streamed);
} else {
options.onToken(piecePayload, null);
}
const piecePayload = emitTokenText
? deltaText
: textEncoder.encode(deltaText);
options.onToken(piecePayload, shouldEmitCurrentText ? fullText : null);
}

if (yieldInterval > 0 && (generated % yieldInterval) === 0) {
Expand All @@ -3909,6 +3936,17 @@ class LlamaWebGpuBridgeRuntime {
}

const text = this._core.ccall('llamadart_webgpu_last_output', 'string', [], []) || streamed || '';
if (typeof options.onToken === 'function') {
const tailText = text.startsWith(emittedStableText)
? text.slice(emittedStableText.length)
: '';
if (tailText.length > 0) {
const piecePayload = emitTokenText
? tailText
: textEncoder.encode(tailText);
options.onToken(piecePayload, shouldEmitCurrentText ? text : null);
}
}
return text;
} finally {
if (generationStarted) {
Expand Down Expand Up @@ -4203,6 +4241,40 @@ export class LlamaWebGpuBridge {
return sanitized;
}

_createCpuSafeMultimodalLoadOptions(options = {}) {
const sanitized = this._sanitizeModelLoadOptions(options);
sanitized.nGpuLayers = 0;

if (Number.isFinite(Number(sanitized.nCtx)) && Number(sanitized.nCtx) > 4096) {
sanitized.nCtx = 4096;
}

if (!Number.isFinite(Number(sanitized.nThreads)) || Number(sanitized.nThreads) <= 0) {
sanitized.nThreads = 4;
} else {
sanitized.nThreads = Math.min(4, Math.max(1, Math.trunc(Number(sanitized.nThreads))));
}

sanitized.nThreadsBatch = sanitized.nThreads;

if (!Number.isFinite(Number(sanitized.nBatch)) || Number(sanitized.nBatch) <= 0) {
sanitized.nBatch = 128;
} else {
sanitized.nBatch = Math.min(128, Math.max(32, Math.trunc(Number(sanitized.nBatch))));
}

if (!Number.isFinite(Number(sanitized.nUbatch)) || Number(sanitized.nUbatch) <= 0) {
sanitized.nUbatch = Math.min(64, sanitized.nBatch);
} else {
sanitized.nUbatch = Math.min(
sanitized.nBatch,
Math.min(64, Math.max(1, Math.trunc(Number(sanitized.nUbatch)))),
);
}

return sanitized;
}

_rememberLoadedModel(url, options = {}) {
const normalizedUrl = String(url || '').trim();
if (normalizedUrl.length === 0) {
Expand Down Expand Up @@ -4277,7 +4349,9 @@ export class LlamaWebGpuBridge {
return false;
}

const selectedOptions = this._sanitizeModelLoadOptions(this._loadedModelOptions || {});
const selectedOptions = this._sanitizeModelLoadOptions(
this._loadedModelOptions || {},
);

const applyWorkerSafeMode = async () => {
await this._callWorker('loadModelFromUrl', [this._loadedModelUrl, selectedOptions]);
Expand Down Expand Up @@ -4381,12 +4455,29 @@ export class LlamaWebGpuBridge {
}

const forceReloadRequested = options?._llamadartForceRuntimeReload === true;
const mediaPartsRequested = this._hasMediaParts(options);
const shouldEnsureMultimodalInRuntime =
this._hasMediaParts(options)
mediaPartsRequested
&& typeof this._loadedMmProjUrl === 'string'
&& this._loadedMmProjUrl.length > 0;
const workerTimedOut = this._isWorkerTimeoutError(fallbackError);
const forcedCpuFallback = this._isForcedCpuMultimodalFallbackError(fallbackError);
const dispatchWorkgroupFallback = this._isDispatchWorkgroupLimitError(fallbackError);
const loadedGpuLayers = Number(this._loadedModelOptions?.nGpuLayers);
const metadataGpuLayers = Number(this._metadata?.['llamadart.webgpu.n_gpu_layers']);
const modelLoadedWithGpu = Number.isFinite(loadedGpuLayers)
? loadedGpuLayers !== 0
: (Number.isFinite(metadataGpuLayers) ? metadataGpuLayers !== 0 : true);
const shouldUseCpuMultimodalFallback =
mediaPartsRequested
&& modelLoadedWithGpu
&& (dispatchWorkgroupFallback || forcedCpuFallback || workerTimedOut);

if (Number(this._runtime?._modelBytes) > 0 && !forceReloadRequested) {
if (
Number(this._runtime?._modelBytes) > 0
&& !forceReloadRequested
&& !shouldUseCpuMultimodalFallback
) {
if (shouldEnsureMultimodalInRuntime) {
const runtimeSupportsMedia =
(typeof this._runtime.supportsVision === 'function' && this._runtime.supportsVision())
Expand All @@ -4407,25 +4498,18 @@ export class LlamaWebGpuBridge {
return;
}

const loadOptions = this._sanitizeModelLoadOptions(this._loadedModelOptions || {});
const workerTimedOut = this._isWorkerTimeoutError(fallbackError);
const forcedCpuFallback = this._isForcedCpuMultimodalFallbackError(fallbackError);
const forceCpuMultimodalFallback =
this._hasMediaParts(options)
&& (this._isDispatchWorkgroupLimitError(fallbackError)
|| forcedCpuFallback)
&& Number(loadOptions.nGpuLayers) !== 0;

if (forceCpuMultimodalFallback) {
loadOptions.nGpuLayers = 0;
if (Number.isFinite(loadOptions.nCtx) && Number(loadOptions.nCtx) > 4096) {
loadOptions.nCtx = 4096;
}

const loadOptions = shouldUseCpuMultimodalFallback
? this._createCpuSafeMultimodalLoadOptions(this._loadedModelOptions || {})
: this._sanitizeModelLoadOptions(this._loadedModelOptions || {});
if (shouldUseCpuMultimodalFallback) {
if (forcedCpuFallback) {
this._emitBridgeWarn(
'llamadart: using CPU fallback for multimodal generation stability.',
);
} else if (workerTimedOut) {
this._emitBridgeWarn(
'llamadart: retrying multimodal generation with CPU fallback after worker timeout.',
);
} else {
this._emitBridgeWarn(
'llamadart: retrying multimodal generation with CPU fallback after WebGPU workgroup limit failure.',
Expand All @@ -4448,7 +4532,7 @@ export class LlamaWebGpuBridge {
if (workerTimedOut) {
this._runtime._runtimeNotes.push('worker_fallback_timeout');
}
if (forceCpuMultimodalFallback) {
if (shouldUseCpuMultimodalFallback) {
this._runtime._runtimeNotes.push('worker_fallback_cpu_multimodal');
}
}
Expand Down
8 changes: 8 additions & 0 deletions src/llama_webgpu_core.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -563,6 +563,14 @@ std::string normalize_media_markers(const std::string & prompt, const size_t med
replace_all_inplace(normalized, "<|image|>", marker);
replace_all_inplace(normalized, "<img>", marker);
replace_all_inplace(normalized, "<|img|>", marker);
replace_all_inplace(
normalized,
"<|vision_start|><|image_pad|><|vision_end|>",
marker);
replace_all_inplace(
normalized,
"<|vision_start|><|video_pad|><|vision_end|>",
marker);
replace_all_inplace(normalized, "<audio>", marker);
replace_all_inplace(normalized, "<|audio|>", marker);

Expand Down
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