Fix inflate operator: Reset max output volume. Use size in bytes, not elements.

[mzient]

Category:

Bug fix (non-breaking change which fixes an issue)

Description:

This PR fixes intermittent failure of inflate operator tests caused by uninitialized variable and improper element size assumptions.

Additional information:

Affected modules and functionalities:

Key points relevant for the review:

test_dali_stateless_operators.test_inflate_stateless

• Existing tests apply
• New tests added
  • Python tests
  • GTests
  • Benchmark
  • Other
• N/A

Checklist

Documentation

• Existing documentation applies
• Documentation updated
  • Docstring
  • Doxygen
  • RST
  • Jupyter
  • Other
• N/A

DALI team only

Requirements

• Implements new requirements
• Affects existing requirements
• N/A

REQ IDs: N/A

JIRA TASK: N/A

[greptile-apps]

Greptile Summary

This PR fixes two bugs in the GPU LZ4 inflate operator: (1) max_output_sample_vol_ was never reset to zero inside ParseOutputShape, so it could carry a stale value from a previous iteration; (2) the two size arguments passed to nvcompBatchedLZ4DecompressGetTempSizeAsync were in elements rather than bytes, causing an under-sized temp buffer and potential decompression failures for any output type wider than uint8.

Confidence Score: 5/5

Safe to merge; both targeted bug fixes are correct and the only remaining finding is a P2 style hardening suggestion.

All root-cause bugs (uninitialized max volume and element-vs-byte mismatch) are correctly addressed. The single comment is a P2 latent edge-case that the operator already guards against in RunImpl, so it does not block merge.

dali/operators/decoder/inflate/inflate_params.h — the early-return path in ParseOutputShape still skips resetting the max-volume accumulators.

Vulnerabilities

No security concerns identified.

Important Files Changed

Filename	Overview
dali/operators/decoder/inflate/inflate_params.h	Adds max_output_sample_vol_ = 0 reset alongside the existing max_output_vol_ = 0 reset, fixing a missing initialisation that could cause stale values on repeated calls; reset is still skipped on the num_samples == 0 early-return path.
dali/operators/decoder/inflate/inflate_gpu.cc	Correctly converts element-count volumes to byte sizes before passing to nvcompBatchedLZ4DecompressGetTempSizeAsync, fixing incorrect temp-buffer sizing for output types wider than uint8.
dali/operators/decoder/inflate/inflate.h	Introduces TypeInfo element_type_ member (initialised in constructor) to provide element byte-size to the GPU implementation; straightforward and correct.

Sequence Diagram

sequenceDiagram
    participant Inflate as "Inflate (GPU)"
    participant Impl as "InflateOpGpuLZ4Impl"
    participant Params as "ShapeParams"
    participant nvcomp as "nvcompBatchedLZ4"

    Inflate->>Impl: "SetupImpl(output_desc, ws)"
    Impl->>Params: "ProcessInputArgs(ws, batch_size)"
    Params->>Params: "ParseOutputShape() - reset max_output_vol_=0, max_output_sample_vol_=0"
    Params-->>Impl: "output shape ready"

    Inflate->>Impl: "RunImpl(ws)"
    Impl->>Params: "GetMaxOutChunkVol() elements"
    Impl->>Params: "GetMaxOutVol() elements"
    Note over Impl: "multiply by element_type_.size() for bytes"
    Impl->>nvcomp: "nvcompBatchedLZ4DecompressGetTempSizeAsync(num_chunks, max_chunk_bytes, params, tempSize, max_total_bytes)"
    nvcomp-->>Impl: "tempSize"
    Impl->>nvcomp: "nvcompBatchedLZ4DecompressAsync(...)"
    nvcomp-->>Impl: "decompressed output"
    Impl->>Impl: "FillTheTails(...)"

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Comments Outside Diff (1)

1. dali/operators/decoder/inflate/inflate_params.h, line 351-356 (link)

   Stale max-volume on empty batch early-return

   When num_samples == 0 the function returns on line 352 before the two reset assignments, so both max_output_vol_ and max_output_sample_vol_ keep whatever values they held from the previous call. If a non-empty batch is processed first and then an empty batch follows, GetMaxOutChunkVol() / GetMaxOutVol() will return stale (oversized) values. RunImpl does guard against empty batches with an early return, so this doesn't cause a crash today, but it is a latent correctness issue.

_{Reviews (1): Last reviewed commit: "Reset max output volume. Use size in byt..." | Re-trigger Greptile}

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