c - Is read/recv thread safe (MSG_PEEK) -

i have 1 thread doing blocking read:

rec = read(socket, data, size); 

i'm curious know whether safe or not me have thread, doing recv(msg_peek) in background on same socket:

while (true) {    if (recv(socket, byte, size, msg_dontwait | msg_peek) > 0)    {        printf("peeked %d", byte);    }    sleep(1); } 

since syscalls operate in kernel space, thread safe (they have be, otherwise kernel data corrupted , bring down entire system) in sense program won't crash - however, noted jeremy friesner in comments:

• the order in syscalls executed may not guaranteed.

• syscalls take time. means lot of data slip past in between calls recv ().

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however, write bytes named fifo. open writing end in thread doing read () , reading end in thread doing recv ().

now, every time complete read (), write first byte (that's wanted, yeah?) fifo. meanwhile, in other thread, instead of using sleep () in between recv (), use blocking read of size 1 byte on fifo , printf () result.

this way, kernel can automatically wake recv () thread whenever there data read. don't waste cpu time unnecessary context switches either (which pretty big), application's overall performance/speed go too.