[UR][CUDA] Fix urUSMContextMemcpyExp synchronization issue#21602
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[UR][CUDA] Fix urUSMContextMemcpyExp synchronization issue#21602
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cuMemcpy is synchronous with respect to the host, but it does not synchronize with device operations in other streams. This can lead to race conditions where urUSMContextMemcpyExp reads stale data if there are pending operations on the source or destination buffers. The issue manifests as sporadic test failures in CI where host_mem reads as 0 instead of the expected value (42), indicating the copy happened before the fill operations completed. Fix: Add cuCtxSynchronize() before cuMemcpy to ensure all pending device operations in the context have completed. This guarantees data consistency at the cost of a device-wide synchronization. Since urUSMContextMemcpyExp is not performance-critical and should provide strong consistency guarantees, this trade-off is acceptable. Fixes #19688 Test: exp_usm_context_memcpy/urUSMContextMemcpyExpTestDevice.Success now passes consistently on CUDA.
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cuMemcpy is synchronous with respect to the host, but it does not synchronize with device operations in other streams. This can lead to race conditions where urUSMContextMemcpyExp reads stale data if there are pending operations on the source or destination buffers.
The issue manifests as sporadic test failures in CI where host_mem reads as 0 instead of the expected value (42), indicating the copy happened before the fill operations completed.
Fix: Add cuCtxSynchronize() before cuMemcpy to ensure all pending device operations in the context have completed. This guarantees data consistency at the cost of a device-wide synchronization.
Since urUSMContextMemcpyExp is not performance-critical and should provide strong consistency guarantees, this trade-off is acceptable.
Fixes #19688
Test: exp_usm_context_memcpy/urUSMContextMemcpyExpTestDevice.Success now passes consistently on CUDA.