Provided by: critcl_3.1.18.1+dfsg-3_amd64 
NAME
critcl::callback - CriTcl C-level Callback Utilities
SYNOPSIS
package require Tcl 8.4
package require critcl ?3.1?
package require critcl::callback ?0.1?
critcl_callback_p critcl_callback_new interp objc objv nargs
void critcl_callback_extend callback argument
void critcl_callback_destroy callback
int critcl_callback_invoke callback objc objv
_________________________________________________________________________________________________
DESCRIPTION
C Runtime In Tcl, or CriTcl , is a system for compiling C code embedded in Tcl on the fly
and either loading the resulting objects into Tcl for immediate use or packaging them for
distribution. Use CriTcl to improve performance by rewriting in C those routines that are
performance bottlenecks.
This document is the reference manpage for the critcl::callback package. This package
provides, via a stubs API table, data structures and functions to manage callbacks from C
to Tcl. The package has no Tcl-level facilities. Its intended audience are mainly
developers wishing to write Tcl packages with embedded C code who have to invoke user-
specified command (prefixes) in Tcl.
This package resides in the Support Package Layer of CriTcl.
+----------------+
|Applications |
| critcl |
| critcl::app |
+----------------+
+----------------+
|Core Packages |
| critcl |
| critcl::util |
+----------------+
*================*
|Support Packages|
| stubs::* |
| md5, platform |
| ... |
*================*
API
The package API consist of one opaque data structure (critcl_callback_p) and four
functions operating on the same. These functions are
critcl_callback_p critcl_callback_new interp objc objv nargs
This function creates a new callback (manager) and returns it as its result.
The callback is initialized with the Tcl_Interp* interp specifying where to run the
callback, the fixed part of the command to run in standard objc/objv notation, plus
the number of free arguments to expect after the fixed part.
The fixed part is the essentially the command prefix of the callback.
All Tcl_Obj* elements of objv are protected against early release by incrementing
their reference counts. The callback effectively takes ownership of these objects.
void critcl_callback_extend callback argument
This function takes a callback of type critcl_callback_p and extends its fixed part
with the argument, taking the first free slot for arguments to do so. This means
that after the application of this function the specified callback has one free
argument less.
With assertions active attempting to extend beyond the number of free arguments
will cause a panic. Without assertions active expect a crash at some point.
This allows the user to extend the fixed part of the callback with semi-fixed
elements, like method names (See Multiple methods).
The argument is protected against early release by incrementing its reference
count. The callback effectively takes ownership of this object.
void critcl_callback_destroy callback
This function takes a callback of type critcl_callback_p and releases all memory
associated with it. After application of this function the callback cannot be used
anymore.
All fixed elements of the callback (owned by it) are released by decrementing their
reference counts.
int critcl_callback_invoke callback objc objv
This function invokes the callback in the Tcl interpreter specified at the time of
construction, in the global level and namespace, with the free arguments filled by
the Tcl_Obj* objects specified via objc/objv.
It returns the Tcl status of the invoked command as its result. Any further
results or error messages will be found in the result area of the Tcl interpreter
in question. The exact nature of such is dependent on the callback itself.
With assertions active attempting to use more arguments than available will cause a
panic. Without assertions active expect a crash at some point.
While the callback is running all Tcl_Obj* elements of the command, fixed and
arguments, are protected against early release by temporarily incrementing their
reference counts.
EXAMPLES
SIMPLE CALLBACK
The example here shows the important parts of using the functions of this package for a
simple callback which is invoked with a single argument, some kind of data to hand to the
Tcl level.
// Create the callback with interpreter and command prefix in
// oc/ov, plus space for the argument
critcl_callback_p cb = critcl_callback_new (interp, oc, ov, 1);
// Invoke the callback somewhere in the C package using this one,
// with Tcl_Obj* data holding the information to pass up.
critcl_callback_invoke (cb, 1, &data);
// At the end of the lifetime, release the callback.
critcl_callback_destroy (cb);
Note that the functions of this package are designed for the case where the created
callback (cb above) is kept around for a long time, and many different invokations.
Using the sequence above as is, creating and destroying the callback each time it is
invoked will yield very poor performance and lots of undesirable memory churn.
MULTIPLE METHODS
While we can use the methodology of the previous section when a single (Tcl-level)
callback is invoked from different places in C, with different methods, simply having
another argument slot and filling it an invokation time with the method object, a second
methodology is open to us due to critcl_callback_extend.
// Create one callback manager per different method the callback
// will be used with. Fill the first of the two declared arguments
// with the different methods.
critcl_callback_p cb_a = critcl_callback_new (interp, oc, ov, 2);
critcl_callback_p cb_b = critcl_callback_new (interp, oc, ov, 2);
critcl_callback_extend (cb_a, Tcl_NewStringObj ("method1", -1));
critcl_callback_extend (cb_b, Tcl_NewStringObj ("method2", -1));
// After the extension we have one free argument left, for use in
// the invokations.
critcl_callback_invoke (cb_a, 1, &dataX);
critcl_callback_invoke (cb_b, 1, &dataY);
// At the end release both managers again
critcl_callback_destroy (cb_a);
critcl_callback_destroy (cb_b);
The nice thing here is that the method objects are allocated only once and automatically
shared by all the calls. No memory churn to repeatedly allocate the same string objects
over and over again.
AUTHORS
Andreas Kupries
BUGS, IDEAS, FEEDBACK
This document, and the package it describes, will undoubtedly contain bugs and other
problems. Please report such at https://github.com/andreas-kupries/critcl. Please also
report any ideas for enhancements you may have for either package and/or documentation.
KEYWORDS
C code, Embedded C Code, code generator, compile & run, compiler, dynamic code generation,
dynamic compilation, generate package, linker, on demand compilation, on-the-fly
compilation
CATEGORY
Glueing/Embedded C code
COPYRIGHT
Copyright (c) 2011-2018 Andreas Kupries