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Asked: 2026-05-19T03:21:50+00:00

I recently asked a question on using volatile and was directed to read some

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I recently asked a question on using volatile and was directed to read some very informative articles from Intel and others discussing memory barriers and their uses. After reading these articles I have become quite paranoid though.

I have a 64-bit machine. Is it safe to memcpy into adjacent, non-overlapping regions of memory from multiple threads? For example, say I have a buffer:

char buff[10];

Is it always safe for one thread to memcpy into the first 5 bytes while a second thread copies into the last 5 bytes?

My gut reaction (and some simple tests) indicate that this is completely safe, but I have been unable to find documentation anywhere that can completely convince me.

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  1. Editorial Team

    Safe, yes. Performant, no- in this limited example, at least. Remember that one cache line cannot be in two cores at once. You will force core A to wait while core B writes to the buffer, and then wait while the memory is transferred, and then write to it. Multi-core memory copies should be very large in size to avoid this effect.

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