Tcl_Interp * Tcl_CreateInterp()
Tcl_CreateInterp creates a new interpreter structure and returns a token for it. The token is required in calls to most other Tcl procedures, such as Tcl_CreateCommand, Tcl_Eval, and Tcl_DeleteInterp. Clients are only allowed to access a few of the fields of Tcl_Interp structures; see the Tcl_Interp and Tcl_CreateCommand man pages for details. The new interpreter is initialized with the built-in Tcl commands and with the variables documented in tclvars. To bind in additional commands, call Tcl_CreateCommand.
Tcl_DeleteInterp marks an interpreter as deleted; the interpreter will eventually be deleted when all calls to Tcl_Preserve for it have been matched by calls to Tcl_Release. At that time, all of the resources associated with it, including variables, procedures, and application-specific command bindings, will be deleted. After Tcl_DeleteInterp returns any attempt to use Tcl_Eval on the interpreter will fail and return TCL_ERROR. After the call to Tcl_DeleteInterp it is safe to examine the interpreter's result, query or set the values of variables, define, undefine or retrieve procedures, and examine the runtime evaluation stack. See below, in the section INTERPRETERS AND MEMORY MANAGEMENT for details.
Tcl_InterpDeleted returns nonzero if Tcl_DeleteInterp was called with interp as its argument; this indicates that the interpreter will eventually be deleted, when the last call to Tcl_Preserve for it is matched by a call to Tcl_Release. If nonzero is returned, further calls to Tcl_Eval in this interpreter will return TCL_ERROR.
Tcl_InterpDeleted is useful in deletion callbacks to distinguish between when only the memory the callback is responsible for is being deleted and when the whole interpreter is being deleted. In the former case the callback may recreate the data being deleted, but this would lead to an infinite loop if the interpreter were being deleted.
Tcl_DeleteInterp can be called at any time on an interpreter that may be used by nested evaluations and C code in various extensions. Tcl implements a simple mechanism that allows callers to use interpreters without worrying about the interpreter being deleted in a nested call, and without requiring special code to protect the interpreter, in most cases. This mechanism ensures that nested uses of an interpreter can safely continue using it even after Tcl_DeleteInterp is called.
The mechanism relies on matching up calls to Tcl_Preserve with calls to Tcl_Release. If Tcl_DeleteInterp has been called, only when the last call to Tcl_Preserve is matched by a call to Tcl_Release, will the interpreter be freed. See the manual entry for Tcl_Preserve for a description of these functions.
The rules for when the user of an interpreter must call Tcl_Preserve and Tcl_Release are simple:
All uses of interpreters in Tcl and Tk have already been protected. Extension writers should ensure that their code also properly protects any additional interpreters used, as described above.