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NAMEpipe pipe2 - create descriptor pair for interprocess communication
SYNOPSISIn unistd.h Ft int Fn pipe int fildes Ft int Fn pipe2 int fildes int flags
DESCRIPTIONThe Fn pipe function creates a pipe which is an object allowing bidirectional data flow, and allocates a pair of file descriptors.
The Fn pipe2 system call allows control over the attributes of the file descriptors via the Fa flags argument. Values for Fa flags are constructed by a bitwise-inclusive OR of flags from the following list, defined in In fcntl.h :
- Set the close-on-exec flag for the new file descriptors.
- Set the non-blocking flag for the ends of the pipe.
If the Fa flags argument is 0, the behavior is identical to a call to Fn pipe .
By convention, the first descriptor is normally used as the read end of the pipe, and the second is normally the write end so that data written to Fa fildes appears on (i.e., can be read from) Fa fildes . This allows the output of one program to be sent to another program: the source's standard output is set up to be the write end of the pipe, and the sink's standard input is set up to be the read end of the pipe. The pipe itself persists until all its associated descriptors are closed.
A pipe that has had an end closed is considered widowed Writing on such a pipe causes the writing process to receive a SIGPIPE signal. Widowing a pipe is the only way to deliver end-of-file to a reader: after the reader consumes any buffered data, reading a widowed pipe returns a zero count.
The bidirectional nature of this implementation of pipes is not portable to older systems, so it is recommended to use the convention for using the endpoints in the traditional manner when using a pipe in one direction.
IMPLEMENTATION NOTESThe Fn pipe function calls the Fn pipe2 system call. As a result, system call traces such as those captured by dtrace(1) or ktrace(1) will show calls to Fn pipe2 .
RETURN VALUESRv -std pipe
ERRORSThe Fn pipe and Fn pipe2 system calls will fail if:
- Bq Er EFAULT
- fildes argument points to an invalid memory location.
- Bq Er EMFILE
- Too many descriptors are active.
- Bq Er ENFILE
- The system file table is full.
- Bq Er ENOMEM
- Not enough kernel memory to establish a pipe.
The Fn pipe2 system call will also fail if:
- Bq Er EINVAL
- The Fa flags argument is invalid.
SEE ALSOsh(1), fork(2), read(2), socketpair(2), write(2)
HISTORYThe Fn pipe function appeared in AT&T System v3 .
Bidirectional pipes were first used on AT&T System V.4 .
The Fn pipe2 function appeared in Fx 10.0 .
The Fn pipe function became a wrapper around Fn pipe2 in Fx 11.0 .