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[Temporary Workaround] Fix pipelined sampling corruption: use per-call execution descriptor #121

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Merged
stikves merged 1 commit into from
Jul 22, 2026
+5 −4
Merged

[Temporary Workaround] Fix pipelined sampling corruption: use per-call execution descriptor #121

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9 changes: 5 additions & 4 deletions swift/Sources/CoreAILanguageModels/Samplers/MPSGraphSamplers.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -496,7 +496,6 @@ final class MPSGraphCompositeSampler: @unchecked Sendable {
private let randomData: MPSGraphTensorData
private let topPData: MPSGraphTensorData
private let minPData: MPSGraphTensorData
private let execDescriptor: MPSGraphExecutableExecutionDescriptor

/// Testing only: Override random value for deterministic tests.
var testingOnlyRandomOverride: Float?
Expand Down Expand Up @@ -678,7 +677,6 @@ final class MPSGraphCompositeSampler: @unchecked Sendable {
shape: [1 as NSNumber],
dataType: .float32
)
self.execDescriptor = MPSGraphExecutableExecutionDescriptor()
}

/// Encode composite sampling asynchronously (protocol conformance).
Expand Down Expand Up @@ -725,7 +723,10 @@ final class MPSGraphCompositeSampler: @unchecked Sendable {
cachedOutputBuffer = outputBuffer
}

execDescriptor.completionHandler = { [outputBuffer, outputOffset] (_, error) in
// Per-call descriptor — reusing one across pipelined steps corrupts
// intermediate scratch buffers when multiple runAsync calls overlap.
let desc = MPSGraphExecutableExecutionDescriptor()
desc.completionHandler = { [outputBuffer, outputOffset] (_, error) in
if let error = error {
print("MPSGraph composite sampler error: \(error)")
completion(0)
Expand All @@ -743,7 +744,7 @@ final class MPSGraphCompositeSampler: @unchecked Sendable {
with: queue,
inputs: [logitsData, temperatureData, randomData, topPData, minPData],
results: [outputData],
executionDescriptor: execDescriptor
executionDescriptor: desc
)
}

Expand Down