On POSIX systems, system calls can be interrupted by signals. In this case,
they'll return EINTR, indicating that the system call needs to be restarted.
(The situation is a little more complicated than this with SA_RESTART, but you
can read man 7 signal if you like.)
The short of it is that you need to catch EINTR and restart the call for these
system calls:
* read, readv, write, writev, ioctl
* open() when dealing with a fifo
* wait*
* Anything socket based (send*, recv*, connect, accept etc)
* flock and lock control with fcntl
* mq_ functions which can block
* futex
* sem_wait (and timed wait)
* pause, sigsuspend, sigtimedwait, sigwaitinfo
* poll, epoll_wait, select and 'p' versions of the same
* msgrcv, msgsnd, semop, semtimedop
* close (although, on Linux, EINTR won't happen here)
* any sleep functions (careful, you need to handle this are restart with
different arguments)
We've been a little sloppy with this until now. Once the tree reopens, I'll be
landing 100225 which adds a macro for dealing with this and corrects every case
of these system calls (that I found).
The macro is HANDLE_EINTR in base/eintr_wrapper.h. It's safe to include on
Windows and is a no-op there.
On POSIX, it uses GCC magic to return the correct type based on the expression
and restarts the system call if it throws EINTR. Here it is:
#define HANDLE_EINTR(x) ({ \
typeof(x) ret; \
do { \
ret = x; \
} while (ret == -1 && errno == EINTR); \
ret;\
})
And you can use it like:
HANDLE_EINTR(close(fd));
Or:
ssize_t bytes_read = HANDLE_EINTR(read(fd, buffer, len));
AGL
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