Tcl 9.0/Tk9.0 Documentation > Tcl Commands, version 9.0.0 > process

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NAME
tcl::process — Subprocess management
SYNOPSIS
DESCRIPTION
::tcl::process autopurge ?flag?
::tcl::process list
::tcl::process purge ?pids?
::tcl::process status ?switches? ?pids?
code
msg
errorCode
-wait
--
EXAMPLES
SEE ALSO
KEYWORDS

NAME

tcl::process — Subprocess management

SYNOPSIS

::tcl::process option ?arg arg ...?

DESCRIPTION

This command provides a way to manage subprocesses created by the open and exec commands, as identified by the process identifiers (PIDs) of those subprocesses. The legal options (which may be abbreviated) are:

::tcl::process autopurge ?flag?
Automatic purge facility. If flag is specified as a boolean value then it activates or deactivate autopurge. In all cases it returns the current status as a boolean value. When autopurge is active, Tcl_ReapDetachedProcs is called each time the exec command is executed or a pipe channel created by open is closed. When autopurge is inactive, ::tcl::process purge must be called explicitly. By default autopurge is active.

::tcl::process list
Returns the list of subprocess PIDs. This includes all currently executing subprocesses and all terminated subprocesses that have not yet had their corresponding process table entries purged.

::tcl::process purge ?pids?
Cleans up all data associated with terminated subprocesses. If pids is specified as a list of PIDs then the command only cleanup data for the matching subprocesses if they exist, and raises an error otherwise. If a process listed is still active, this command does nothing to that process.

::tcl::process status ?switches? ?pids?
Returns a dictionary mapping subprocess PIDs to their respective status. If pids is specified as a list of PIDs then the command only returns the status of the matching subprocesses if they exist, and raises an error otherwise. For active processes, the status is an empty value. For terminated processes, the status is a list with the following format: “{code ?msg errorCode?}”, where:

code
is a standard Tcl return code, i.e., 0 for TCL_OK and 1 for TCL_ERROR,

msg
is the human-readable error message,

errorCode
uses the same format as the errorCode global variable

Note that msg and errorCode are only present for abnormally terminated processes (i.e. those where the code is nonzero). Under the hood this command calls Tcl_WaitPid with the WNOHANG flag set for non-blocking behavior, unless the -wait switch is set (see below).

Additionally, ::tcl::process status accepts the following switches:

-wait
By default the command returns immediately (the underlying Tcl_WaitPid is called with the WNOHANG flag set) unless this switch is set. If pids is specified as a list of PIDs then the command waits until the status of the matching subprocesses are available. If pids was not specified, this command will wait for all known subprocesses.

--
Marks the end of switches. The argument following this one will be treated as the first arg even if it starts with a -.

EXAMPLES

These show the use of ::tcl::process. Some of the results from ::tcl::process status are split over multiple lines for readability. 

::tcl::process autopurge
     → true
::tcl::process autopurge false
     → false

set pid1 [exec command1 a b c | command2 d e f &]
     → 123 456
set chan [open "|command1 a b c | command2 d e f"]
     → file123
set pid2 [pid $chan]
     → 789 1011

::tcl::process list
     → 123 456 789 1011

::tcl::process status
     → 123 0
       456 {1 "child killed: write on pipe with no readers" {
         CHILDKILLED 456 SIGPIPE "write on pipe with no readers"}}
       789 {1 "child suspended: background tty read" {
         CHILDSUSP 789 SIGTTIN "background tty read"}}
       1011 {}

::tcl::process status 123
     → 123 0

::tcl::process status 1011
     → 1011 {}

::tcl::process status -wait
     → 123 0
       456 {1 "child killed: write on pipe with no readers" {
         CHILDKILLED 456 SIGPIPE "write on pipe with no readers"}}
       789 {1 "child suspended: background tty read" {
         CHILDSUSP 789 SIGTTIN "background tty read"}}
       1011 {1 "child process exited abnormally" {
         CHILDSTATUS 1011 -1}}

::tcl::process status 1011
     → 1011 {1 "child process exited abnormally" {
         CHILDSTATUS 1011 -1}}

::tcl::process purge
exec command1 1 2 3 &
     → 1213
::tcl::process list
     → 1213

SEE ALSO

exec, open, pid, Tcl_DetachPids, Tcl_WaitPid, Tcl_ReapDetachedProcs

KEYWORDS

background, child, detach, process, wait
Copyright © 2017 Frederic Bonnet.