Document File thread safety about zbox HOT 3 CLOSED

Can you post your full source code? Without details, it's hard to see what's the actual problem is.

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Well just looking it at the code makes it obvious: a File can't receive consecutive writes from different threads, since begin_write() initializes a thread local TXID, which will not be set on a second write from a different thread.

So with the current design, File should really be !Send.

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Your looking is right. When shared with multiple threads, File works like a reader-writer lock, that is, you can only have one thread to modify it, but you can have multiple threads to read. So I think !Send is still valid.

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