## Tcl8.6.15/Tk8.6.15 Documentation > Tcl C API, version 8.6.15 > CrtTimerHdlr

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  NAME
    Tcl_CreateTimerHandler, Tcl_DeleteTimerHandler — call a procedure at a given time
  SYNOPSIS
    #include <tcl.h>
    Tcl_TimerToken
    Tcl_CreateTimerHandler(milliseconds, proc, clientData)
    Tcl_DeleteTimerHandler(token)
  ARGUMENTS
  DESCRIPTION
  SEE ALSO
  KEYWORDS

### NAME

Tcl_CreateTimerHandler, Tcl_DeleteTimerHandler — call a procedure at a given time

### SYNOPSIS

#include <tcl.h>
Tcl_TimerToken
Tcl_CreateTimerHandler(milliseconds, proc, clientData)
Tcl_DeleteTimerHandler(token)

### ARGUMENTS

int milliseconds (in)
  How many milliseconds to wait before invoking proc.

Tcl_TimerProc *proc (in)
  Procedure to invoke after milliseconds have elapsed.

ClientData clientData (in)
  Arbitrary one-word value to pass to proc.

Tcl_TimerToken token (in)
  Token for previously created timer handler (the return value from some previous call to Tcl_CreateTimerHandler).

### DESCRIPTION

Tcl_CreateTimerHandler arranges for proc to be invoked at a time milliseconds milliseconds in the future. The callback to proc will be made by Tcl_DoOneEvent, so Tcl_CreateTimerHandler is only useful in programs that dispatch events through Tcl_DoOneEvent or through Tcl commands such as vwait. The call to proc may not be made at the exact time given by milliseconds: it will be made at the next opportunity after that time. For example, if Tcl_DoOneEvent is not called until long after the time has elapsed, or if there are other pending events to process before the call to proc, then the call to proc will be delayed.

Proc should have arguments and return value that match the type Tcl_TimerProc:

    typedef void Tcl_TimerProc(
            ClientData clientData);

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

Tcl_DeleteTimerHandler may be called to delete a previously created timer handler. It deletes the handler indicated by token so that no call to proc will be made; if that handler no longer exists (e.g. because the time period has already elapsed and proc has been invoked then Tcl_DeleteTimerHandler does nothing. The tokens returned by Tcl_CreateTimerHandler never have a value of NULL, so if NULL is passed to Tcl_DeleteTimerHandler then the procedure does nothing.

### SEE ALSO

after, Tcl_CreateFileHandler, Tcl_DoWhenIdle

### KEYWORDS

callback, clock, handler, timer
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