CODEWITHSUNDEEP
csockets
Francisco Ryan Tolmasky I
Francisco Ryan Tolmasky I

Reputation: 6183

Can I free my data immediately after send() in blocking mode?

the docs say for send:

When the message does not fit into the send buffer of the socket, send() normally blocks, unless the socket has been placed in non-block- ing I/O mode. In non-blocking mode it would return EAGAIN in this case. The select(2) call may be used to determine when it is possible to send more data.

I am in blocking mode, doing something along the lines of:

buf = malloc(size);

send (socket, buf, size);

free(buf)

Assume but is very large, larger than the buffer can hold at a time (so it would need to go into the buffer as two chunks lets say). Anyways, in blocking mode, which I'm in, after send, can I feel safe that the data is fully copied or dealt with and thus deletable?

Upvotes: 2

Views: 254

Answers (2)

mcleod_ideafix
mcleod_ideafix

Reputation: 11448

In blocking mode, send blocks until I/O is complete, or an error is triggered. You should check the returned value, because a send operation does not guarantee that the number of bytes sent is the same number of bytes passed as third argument.

Only when send returns a value equal to the size of the buffer sent you can be sure that the whole block has been copied into kernel memory, or passed through device memory, or sent to the destination.

Upvotes: 5

pah
pah

Reputation: 4778

The short answer is: Yes, you can free the buffer after the send() call successfully returns (without errors) when the file descriptor is in blocking mode.

The reason for this is based on the blocking concept itself: The send() call (targeting a blocking file descriptor) will only return when an error occur or the requested size bytes of the data in the buf is buffered or transmitted by the underlying layer of the operating system (typically the kernel).

Also note that a successful return of send() doesn't mean that the data was transmitted. It means that it was, at least, buffered by the underlying layer.

Upvotes: 1

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