Tcl_DetachPids(), Tcl_ReapDetachedProcs()

manage child processes in background 

Tcl Library Procedures


#include <tcl.h>

Tcl_DetachPids(numPids, pidPtr)



int numPids (in) 

Number of process ids contained in the array pointed to by pidPtr.

int *pidPtr (in) 

Address of array containing numPids process ids.


Tcl_DetachPids() and Tcl_ReapDetachedProcs() provide a mechanism for managing subprocesses that are running in background. These procedures are needed because the parent of a process must eventually invoke the waitpid kernel call (or one of a few other similar kernel calls) to wait for the child to exit. Until the parent waits for the child, the child's state cannot be completely reclaimed by the system. If a parent continually creates children and doesn't wait on them, the system's process table will eventually overflow, even if all the children have exited.

Tcl_DetachPids() may be called to ask Tcl to take responsibility for one or more processes whose process ids are contained in the pidPtr array passed as argument. The caller presumably has started these processes running in background and doesn't want to have to deal with them again.

Tcl_ReapDetachedProcs() invokes the waitpid kernel call on each of the background processes so that its state can be cleaned up if it has exited. If the process hasn't exited yet, Tcl_ReapDetachedProcs() doesn't wait for it to exit; it will check again the next time it is invoked. Tcl automatically calls Tcl_ReapDetachedProcs() each time the exec command is executed, so in most cases it isn't necessary for any code outside of Tcl to invoke Tcl_ReapDetachedProcs(). However, if you call Tcl_DetachPids() in situations where the exec command may never get executed, you may wish to call Tcl_ReapDetachedProcs() from time to time so that background processes can be cleaned up.


Windows 8.1. Windows Server 2012 R2. Windows 10. Windows Server 2016. Windows Server 2019. Windows 11. Windows Server 2022.


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