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.\" Copyright 2015 Joyent, Inc.
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.Dd November 27, 2023
.Dt PROC_INITSTDIO 3PROC
.Os
.Sh NAME
.Nm proc_initstdio ,
.Nm proc_flushstdio ,
.Nm proc_finistdio
.Nd stdio buffering functions
.Sh LIBRARY
.Lb libproc
.Sh SYNOPSIS
.In 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.
.Pp
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.
.Pp
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.
.Pp
The
.Fn proc_initstdio
function initializes a new standard out and standard error file
descriptors and retains the originals.
.Pp
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.
.Pp
The
.Fn proc_finistdio
flushes any outstanding I/O and restores the original standard output
and standard error.
.Pp
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