Tcl_Exit, Tcl_Finalize, Tcl_CreateExitHandler, Tcl_DeleteExitHandler, Tcl_ExitThread, Tcl_FinalizeThread, Tcl_CreateThreadExitHandler, Tcl_DeleteThreadExitHandler, Tcl_SetExitProc − end the application or thread (and invoke exit handlers)


#include <tcl.h>



Tcl_CreateExitHandler(proc, clientData)

Tcl_DeleteExitHandler(proc, clientData)



Tcl_CreateThreadExitHandler(proc, clientData)

Tcl_DeleteThreadExitHandler(proc, clientData)

Tcl_ExitProc * │
(proc) │


int status (in)

Provides information about why the application or thread exited. Exact meaning may be platform-specific. 0 usually means a normal exit, any nonzero value usually means that an error occurred.

Tcl_ExitProc *proc (in)

Procedure to invoke before exiting application, or (for Tcl_SetExitProc) NULL to uninstall the current application exit procedure.

ClientData clientData (in)

Arbitrary one-word value to pass to proc.



The procedures described here provide a graceful mechanism to end the execution of a Tcl application. Exit handlers are invoked to cleanup the application’s state before ending the execution of Tcl code.

Invoke Tcl_Exit to end a Tcl application and to exit from this process. This procedure is invoked by the exit command, and can be invoked anyplace else to terminate the application. No-one should ever invoke the exit system procedure directly; always invoke Tcl_Exit instead, so that it can invoke exit handlers. Note that if other code invokes exit system procedure directly, or otherwise causes the application to terminate without calling Tcl_Exit, the exit handlers will not be run. Tcl_Exit internally invokes the exit system call, thus it never returns control to its caller. If an application exit handler has been │ installed (see Tcl_SetExitProc), that handler is invoked with an │ argument consisting of the exit status (cast to ClientData); the │ application exit handler should not return control to Tcl.

Tcl_Finalize is similar to Tcl_Exit except that it does not exit from the current process. It is useful for cleaning up when a process is finished using Tcl but wishes to continue executing, and when Tcl is used in a dynamically loaded extension that is about to be unloaded. On some systems Tcl is automatically notified when it is being unloaded, and it calls Tcl_Finalize internally; on these systems it not necessary for the caller to explicitly call Tcl_Finalize. However, to ensure portability, your code should always invoke Tcl_Finalize when Tcl is being unloaded, to ensure that the code will work on all platforms. Tcl_Finalize can be safely called more than once.

Tcl_ExitThread is used to terminate the current thread and invoke per-thread exit handlers. This finalization is done by Tcl_FinalizeThread, which you can call if you just want to clean up per-thread state and invoke the thread exit handlers. Tcl_Finalize calls Tcl_FinalizeThread for the current thread automatically.

Tcl_CreateExitHandler arranges for proc to be invoked by Tcl_Finalize and Tcl_Exit. Tcl_CreateThreadExitHandler arranges for proc to be invoked by Tcl_FinalizeThread and Tcl_ExitThread. This provides a hook for cleanup operations such as flushing buffers and freeing global memory. Proc should match the type Tcl_ExitProc:

typedef void Tcl_ExitProc(ClientData clientData);

The clientData parameter to proc is a copy of the clientData argument given to Tcl_CreateExitHandler or Tcl_CreateThreadExitHandler when the callback was created. Typically, clientData points to a data structure containing application-specific information about what to do in proc.

Tcl_DeleteExitHandler and Tcl_DeleteThreadExitHandler may be called to delete a previously-created exit handler. It removes the handler indicated by proc and clientData so that no call to proc will be made. If no such handler exists then Tcl_DeleteExitHandler or Tcl_DeleteThreadExitHandler does nothing.

Tcl_Finalize and Tcl_Exit execute all registered exit handlers, in reverse order from the order in which they were registered. This matches the natural order in which extensions are loaded and unloaded; if extension A loads extension B, it usually unloads B before it itself is unloaded. If extension A registers its exit handlers before loading extension B, this ensures that any exit handlers for B will be executed before the exit handlers for A.

Tcl_Finalize and Tcl_Exit call Tcl_FinalizeThread and the thread exit handlers after the process-wide exit handlers. This is because thread finalization shuts down the I/O channel system, so any attempt at I/O by the global exit handlers will vanish into the bitbucket.

Tcl_SetExitProc installs an application exit handler, returning the │ previously-installed application exit handler or NULL if no application │ handler was installed. If an application exit handler is installed, │ that exit handler takes over complete responsibility for finalization │ of Tcl’s subsystems via Tcl_Finalize at an appropriate time. The │ argument passed to proc when it is invoked will be the exit status code │ (as passed to Tcl_Exit) cast to a ClientData value.


callback, cleanup, dynamic loading, end application, exit, unloading, thread


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