what exactly is "block" mean

feetyouwell · 09-29-2004, 09:06 PM

I have encountered many "block"s while reading the linux programming book. what does it exactly mean?
for example, i am reading upon how to use waitpid(pid_t, int *, int)
the 3rd int which is a flag could contain WHOHANG, and WUNTRACED
the book says "WHOHANG return immediately if no child has exited - do not block if the status cannot be obtained; return a value of 0, not the PID.
WUNTRACED return immediately if child is blocked"

can anyone explain to me what those "blocked" means here? thanks

itsme86 · 09-29-2004, 09:16 PM

"block" means it freezes the process. Like, if you did "getchar();" it would block the process until the user hit ENTER. So when you call waitpid(), it will block the process until the child exits -- it waits for the child. If the child has already exited by the time you call waitpid() then waitpid() will not block -- it will return right away. Does that make sense?

feetyouwell · 09-29-2004, 09:38 PM

yes it does, thanks for all of your help man