ocean.sys.SignalFD

Linux signal file descriptor event.

signalfd man page follows:

signalfd() creates a file descriptor that can be used to accept signals targeted at the caller. This provides an alternative to the use of a signal handler or sigwaitinfo(2), and has the advantage that the file descriptor may be monitored by select(2), poll(2), and epoll(7).

The mask argument specifies the set of signals that the caller wishes to accept via the file descriptor. This argument is a signal set whose contents can be initialized using the macros described in sigsetops(3). Normally, the set of signals to be received via the file descriptor should be blocked using sigprocmask(2), to prevent the signals being handled according to their default dispositions. It is not possible to receive SIGKILL or SIGSTOP signals via a signalfd file descriptor; these signals are silently ignored if specified in mask.

If the fd argument is -1, then the call creates a new file descriptor and associates the signal set specified in mask with that descriptor. If fd is not -1, then it must specify a valid existing signalfd file descriptor, and mask is used to replace the signal set associated with that descriptor.

Starting with Linux 2.6.27, the following values may be bitwise ORed in flags to change the behaviour of signalfd():

SFD_NONBLOCK Set the O_NONBLOCK file status flag on the new open file description. Using this flag saves extra calls to fcntl(2) to achieve the same result.

SFD_CLOEXEC Set the close-on-exec (FD_CLOEXEC) flag on the new file descriptor. See the description of the O_CLOEXEC flag in open(2) for reasons why this may be useful.

In Linux up to version 2.6.26, the flags argument is unused, and must be specified as zero.

signalfd() returns a file descriptor that supports the following operations:

read(2) If one or more of the signals specified in mask is pending for the process, then the buffer supplied to read(2) is used to return one or more signalfd_siginfo structures (see below) that describe the signals. The read(2) returns information for as many signals as are pending and will fit in the supplied buffer. The buffer must be at least sizeof(struct signalfd_siginfo) bytes. The return value of the read(2) is the total number of bytes read.

As a consequence of the read(2), the signals are consumed, so that they are no longer pending for the process (i.e., will not be caught by signal handlers, and cannot be accepted using sigwaitinfo(2)).

If none of the signals in mask is pending for the process, then the read(2) either blocks until one of the signals in mask is generated for the process, or fails with the error EAGAIN if the file descriptor has been made nonblocking.

poll(2), select(2) (and similar) The file descriptor is readable (the select(2) readfds argument; the poll(2) POLLIN flag) if one or more of the signals in mask is pending for the process.

The signalfd file descriptor also supports the other file-descriptor multiplexing APIs: pselect(2), ppoll(2), and epoll(7).

close(2) When the file descriptor is no longer required it should be closed. When all file descriptors associated with the same signalfd object have been closed, the resources for object are freed by the kernel.