- ClientData clientData (in)
Token describing structure to be freed or reallocated. Usually a pointer to memory for structure.
- Tcl_FreeProc *freeProc (in)
Procedure to invoke to free clientData.
These three procedures help implement a simple reference count mechanism for managing storage. They are designed to solve a problem having to do with widget deletion, but are also useful in many other situations. When a widget is deleted, its widget record (the structure holding information specific to the widget) must be returned to the storage allocator. However, it's possible that the widget record is in active use by one of the procedures on the stack at the time of the deletion. This can happen, for example, if the command associated with a button widget causes the button to be destroyed: an X event causes an event-handling C procedure in the button to be invoked, which in turn causes the button's associated Tcl command to be executed, which in turn causes the button to be deleted, which in turn causes the button's widget record to be de-allocated. Unfortunately, when the Tcl command returns, the button's event-handling procedure will need to reference the button's widget record. Because of this, the widget record must not be freed as part of the deletion, but must be retained until the event-handling procedure has finished with it. In other situations where the widget is deleted, it may be possible to free the widget record immediately.
All the work of freeing the object is carried out by freeProc. FreeProc must have arguments and result that match the type Tcl_FreeProc:
typedef void Tcl_FreeProc(char *blockPtr);
The blockPtr argument to freeProc will be the
same as the clientData argument to
This mechanism can be used to solve the problem described above
Windows Server 2012. Windows 8.1. Windows Server 2012 R2. Windows 10. Windows Server 2016. Windows Server 2019.
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