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NAME | C SYNOPSIS | CAVEAT | DESCRIPTION | DIAGNOSTICS | SEE ALSO | COLOPHON |
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PMPROCESSEXEC(3) Library Functions Manual PMPROCESSEXEC(3)
__pmProcessAddArg, __pmProcessUnpickArgs, __pmProcessExec -
process execution support
#include "pmapi.h"
#include "libpcp.h"
int __pmProcessAddArg(__pmExecCtl_t **handle, const char *arg);
int __pmProcessUnpickArgs(__pmExecCtl_t **handle, const char
*command);
int __pmProcessExec(__pmExecCtl_t **handle, int toss, int wait);
cc ... -lpcp
This documentation is intended for internal Performance Co-Pilot
(PCP) developer use.
These interfaces are not part of the PCP APIs that are guaranteed
to remain fixed across releases, and they may not work, or may
provide different semantics at some point in the future.
Within the libraries and applications of the Performance Co-Pilot
(PCP) these routines are provide a convenient and safe alternative
to system(3) for executing commands in a separate process.
Use __pmProcessAddArg to register the executable and command
arguments in order. handle should be set to NULL before the first
call to __pmProcessAddArg for a particular command execution and
it will be set to an opaque pointer to data structures that are
manipulated in __pmProcessAddArg, __pmProcessExec and the related
__pmProcessPipe(3) routines.
When called with handle set to NULL arg is treated as the name of
the command to be executed and subsequent calls (if any) are for
the arguments to that command. The name of the command can be a
full pathname, or the name of an executable that can be found on
the current $PATH as per the rules of execvp(2) that is used by
__pmProcessExec.
__pmProcessUnpickArgs is a convenience wrapper to assist
conversion of code that assumes the command is a shell command
that has been prepared for use with system(3) or popen(3) in
existing code. The arguments in command are picked off one-by-one
and used to call __pmProcessAddArg. The parser is simple, as the
routine is designed for simple shell command syntax, where
arguments are separated by one or more spaces but embedded spaces
within an argument are allowed if the argument is enclosed in
single or double quotes. More advanced shell syntax like escape
characters and input-output redirection are not recognized.
Once all the command name and arguments have been registered
calling __pmProcessExec uses a fork(2) and execvp(2) sequence to
execute the command.
The argument toss may be used to assign some or all of the
standard I/O streams for the command to /dev/null - specifically
toss is either PM_EXEC_TOSS_NONE to keep all I/O streams the same
as the parent process, else the bit-wise or of PM_EXEC_TOSS_STDIN
and/or PM_EXEC_TOSS_STDOUT and/or PM_EXEC_TOSS_STDERR to reassign
stdin, stdout and stderr respectively. PM_EXEC_TOSS_ALL is a
convenience macro equivalent to PM_EXEC_TOSS_STDIN |
PM_EXEC_TOSS_STDOUT | PM_EXEC_TOSS_STDERR.
The wait argument should be PM_EXEC_WAIT if __pmProcessExec should
wait for completion of the command and harvest the exit status,
else PM_EXEC_NOWAIT in which case __pmProcessExec returns
immediately (effectively running the command in the background).
Nested calling of __pmProcessExec and/or __pmProcessPipe(3) is not
allowed. Once __pmProcessAddArg is called with handle set to NULL
to start the registration and execution sequence any attempt to
start a second registration sequence will be blocked until the
first one is completed by calling __pmProcessExec or
__pmProcessPipe(3).
If successful __pmProcessAddArg returns 0. Other conditions are
rare (e.g. memory allocation failure) and are indicated by a
return value that can be decoded using pmErrStr(3). When an error
does occur __pmProcessAddArg cleans up any allocations made in the
current call and uses handle to clean up any allocations made by
previous calls so there is no need for the caller to worry about
memory leaks, and then (re)sets handle to NULL before returning.
__pmProcessUnpickArgs returns 0 on success. In the case of an
unterminated string, a message is generated and PM_ERR_GENERIC is
returned. Other return values less than 0 indicate a more serious
error and the value can be decoded using pmErrStr(3). When an
error does occur the clean up is similar to __pmProcessAddArg so
there is no need for the caller to worry about memory leaks.
The return status from __pmProcessExec is more complicated. If
either PM_EXEC_NOWAIT is specified, or the command completes with
an exit status of 0, the return value is 0. Return values less
than 0 indicate a more serious error and the value can be decoded
using pmErrStr(3). If the command was executed, but did not exit
with status of 0 then the return value is an encoding of the
waitpid(2) status as follows: 2000 if something unknown went
wrong, else if 1000 + signal number of the command was killed or
stopped by a signal, else the exit status of the command.
execvp(2), fork(2), __pmProcessPipe(3), popen(3), system(3) and
waitpid(3).
This page is part of the PCP (Performance Co-Pilot) project.
Information about the project can be found at
⟨http://www.pcp.io/⟩. If you have a bug report for this manual
page, send it to pcp@groups.io. This page was obtained from the
project's upstream Git repository
⟨https://github.com/performancecopilot/pcp.git⟩ on 2025-02-02.
(At that time, the date of the most recent commit that was found
in the repository was 2025-01-30.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
Performance Co-Pilot PCP PMPROCESSEXEC(3)
Pages that refer to this page: __pmprocesspipe(3)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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