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.Dd May 11, 2016 .Dt PROC_INITSTDIO 3PROC .Os .Sh NAME .Nm proc_initstdio , .Nm proc_flushstdio , .Nm proc_finistdio .Nd stdio buffering functions .Sh SYNOPSIS .Lb libproc n libproc.h .Ft int .Fo proc_initstdio .Fa void .Fc .Ft int .Fo proc_flushstdio .Fa void .Fc .Ft int .Fo proc_finistdio .Fa void .Fc .Sh DESCRIPTION The .Fn proc_initstdio , .Fn proc_flushstdio , and .Fn proc_finistdio functions are utilities provided to aid with the possibility of deadlock while doing I/O operations. If a process is trying to do I/O, but holding the process handle that would consume that I/O, then eventually the program holding the process handle will block as none of its I/O has been drained. However, because it is holding a process handle to that process, it will never be drained.

p Consider, for example, the following invocation: .Li pfiles `pgrep xterm` where the command was launched from a shell on an xterm. Because the xterm is stopped, it will not be able to write out any of the standard out that gets passed to it, leading to a deadlock. The .Li pfiles program cannot release the .Li xterm process because it still has pending I/O, but the I/O cannot be drained due to the same hold.

p To address this, these functions duplicate the standard output and standard error of the process to temporary files and then flushes it out to the original file descriptors and streams later. When finished, the original file descriptors are restored as standard out and standard error.

p The .Fn proc_initstdio function initializes a new standard out and standard error file descriptors and retains the originals.

p The .Fn proc_flushstdio functions flushes all of the cached data from the temporary standard out and standard error back to the underlying ones. This function should only be called after all process handles have been released. For example, if iterating on multiple processes, calling this after handling each one is safe.

p The .Fn proc_finistdio flushes any outstanding I/O and restores the original standard output and standard error.

p Once called, the .Fn proc_initstdio function must not be called again until a successful call to .Fn proc_finistdio . .Sh RETURN VALUES Upon successful completion, the .Fn proc_initstdio , .Fn proc_flushstdio , and .Fn proc_finistdio functions all return .Sy 0 . Otherwise, .Sy -1 is returned to indicate failure. .Sh INTERFACE STABILITY .Sy Uncommitted .Sh MT-LEVEL .Sy Unsafe .Sh SEE ALSO .Xr libproc 3LIB , .Xr Pgrab 3PROC , .Xr Prelease 3PROC