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9 | '\" | |
10 | '\" The definitions below are for supplemental macros used in Tcl/Tk | |
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73 | '\" # Set up traps and other miscellaneous stuff for Tcl/Tk man pages. | |
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208 | .SH "STANDARD OPTIONS" | |
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219 | See the \\fBoptions\\fR manual entry for details on the standard options. | |
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245 | .. | |
246 | .TH Tcl_AsyncCreate 3 7.0 Tcl "Tcl Library Procedures" | |
247 | .BS | |
248 | .SH NAME | |
249 | Tcl_AsyncCreate, Tcl_AsyncMark, Tcl_AsyncInvoke, Tcl_AsyncDelete, Tcl_AsyncReady \- handle asynchronous events | |
250 | .SH SYNOPSIS | |
251 | .nf | |
252 | \fB#include <tcl.h>\fR | |
253 | .sp | |
254 | Tcl_AsyncHandler | |
255 | \fBTcl_AsyncCreate\fR(\fIproc, clientData\fR) | |
256 | .sp | |
257 | \fBTcl_AsyncMark\fR(\fIasync\fR) | |
258 | .sp | |
259 | int | |
260 | \fBTcl_AsyncInvoke\fR(\fIinterp, code\fR) | |
261 | .sp | |
262 | \fBTcl_AsyncDelete\fR(\fIasync\fR) | |
263 | .sp | |
264 | int | |
265 | \fBTcl_AsyncReady\fR() | |
266 | .SH ARGUMENTS | |
267 | .AS Tcl_AsyncHandler clientData | |
268 | .AP Tcl_AsyncProc *proc in | |
269 | Procedure to invoke to handle an asynchronous event. | |
270 | .AP ClientData clientData in | |
271 | One-word value to pass to \fIproc\fR. | |
272 | .AP Tcl_AsyncHandler async in | |
273 | Token for asynchronous event handler. | |
274 | .AP Tcl_Interp *interp in | |
275 | Tcl interpreter in which command was being evaluated when handler was | |
276 | invoked, or NULL if handler was invoked when there was no interpreter | |
277 | active. | |
278 | .AP int code in | |
279 | Completion code from command that just completed in \fIinterp\fR, | |
280 | or 0 if \fIinterp\fR is NULL. | |
281 | .BE | |
282 | ||
283 | .SH DESCRIPTION | |
284 | .PP | |
285 | These procedures provide a safe mechanism for dealing with | |
286 | asynchronous events such as signals. | |
287 | If an event such as a signal occurs while a Tcl script is being | |
288 | evaluated then it isn't safe to take any substantive action to | |
289 | process the event. | |
290 | For example, it isn't safe to evaluate a Tcl script since the | |
291 | interpreter may already be in the middle of evaluating a script; | |
292 | it may not even be safe to allocate memory, since a memory | |
293 | allocation could have been in progress when the event occurred. | |
294 | The only safe approach is to set a flag indicating that the event | |
295 | occurred, then handle the event later when the world has returned | |
296 | to a clean state, such as after the current Tcl command completes. | |
297 | .PP | |
298 | \fBTcl_AsyncCreate\fR, \fBTcl_AsyncDelete\fR, and \fBTcl_AsyncReady\fR | |
299 | are thread sensitive. They access and/or set a thread-specific data | |
300 | structure in the event of a core built with \fI\-\-enable\-threads\fR. The token | |
301 | created by \fBTcl_AsyncCreate\fR contains the needed thread information it | |
302 | was called from so that calling \fBTcl_AsyncMark\fR(\fItoken\fR) will only yield | |
303 | the origin thread into the asynchronous handler. | |
304 | .PP | |
305 | \fBTcl_AsyncCreate\fR creates an asynchronous handler and returns | |
306 | a token for it. | |
307 | The asynchronous handler must be created before | |
308 | any occurrences of the asynchronous event that it is intended | |
309 | to handle (it is not safe to create a handler at the time of | |
310 | an event). | |
311 | When an asynchronous event occurs the code that detects the event | |
312 | (such as a signal handler) should call \fBTcl_AsyncMark\fR with the | |
313 | token for the handler. | |
314 | \fBTcl_AsyncMark\fR will mark the handler as ready to execute, but it | |
315 | will not invoke the handler immediately. | |
316 | Tcl will call the \fIproc\fR associated with the handler later, when | |
317 | the world is in a safe state, and \fIproc\fR can then carry out | |
318 | the actions associated with the asynchronous event. | |
319 | \fIProc\fR should have arguments and result that match the | |
320 | type \fBTcl_AsyncProc\fR: | |
321 | .CS | |
322 | typedef int Tcl_AsyncProc( | |
323 | ClientData \fIclientData\fR, | |
324 | Tcl_Interp *\fIinterp\fR, | |
325 | int \fIcode\fR); | |
326 | .CE | |
327 | The \fIclientData\fR will be the same as the \fIclientData\fR | |
328 | argument passed to \fBTcl_AsyncCreate\fR when the handler was | |
329 | created. | |
330 | If \fIproc\fR is invoked just after a command has completed | |
331 | execution in an interpreter, then \fIinterp\fR will identify | |
332 | the interpreter in which the command was evaluated and | |
333 | \fIcode\fR will be the completion code returned by that | |
334 | command. | |
335 | The command's result will be present in the interpreter's result. | |
336 | When \fIproc\fR returns, whatever it leaves in the interpreter's result | |
337 | will be returned as the result of the command and the integer | |
338 | value returned by \fIproc\fR will be used as the new completion | |
339 | code for the command. | |
340 | .PP | |
341 | It is also possible for \fIproc\fR to be invoked when no interpreter | |
342 | is active. | |
343 | This can happen, for example, if an asynchronous event occurs while | |
344 | the application is waiting for interactive input or an X event. | |
345 | In this case \fIinterp\fR will be NULL and \fIcode\fR will be | |
346 | 0, and the return value from \fIproc\fR will be ignored. | |
347 | .PP | |
348 | The procedure \fBTcl_AsyncInvoke\fR is called to invoke all of the | |
349 | handlers that are ready. | |
350 | The procedure \fBTcl_AsyncReady\fR will return non-zero whenever any | |
351 | asynchronous handlers are ready; it can be checked to avoid calls | |
352 | to \fBTcl_AsyncInvoke\fR when there are no ready handlers. | |
353 | Tcl calls \fBTcl_AsyncReady\fR after each command is evaluated | |
354 | and calls \fBTcl_AsyncInvoke\fR if needed. | |
355 | Applications may also call \fBTcl_AsyncInvoke\fR at interesting | |
356 | times for that application. | |
357 | For example, Tcl's event handler calls \fBTcl_AsyncReady\fR | |
358 | after each event and calls \fBTcl_AsyncInvoke\fR if needed. | |
359 | The \fIinterp\fR and \fIcode\fR arguments to \fBTcl_AsyncInvoke\fR | |
360 | have the same meaning as for \fIproc\fR: they identify the active | |
361 | interpreter, if any, and the completion code from the command | |
362 | that just completed. | |
363 | .PP | |
364 | \fBTcl_AsyncDelete\fR removes an asynchronous handler so that | |
365 | its \fIproc\fR will never be invoked again. | |
366 | A handler can be deleted even when ready, and it will still | |
367 | not be invoked. | |
368 | .PP | |
369 | If multiple handlers become active at the same time, the | |
370 | handlers are invoked in the order they were created (oldest | |
371 | handler first). | |
372 | The \fIcode\fR and the interpreter's result for later handlers | |
373 | reflect the values returned by earlier handlers, so that | |
374 | the most recently created handler has last say about | |
375 | the interpreter's result and completion code. | |
376 | If new handlers become ready while handlers are executing, | |
377 | \fBTcl_AsyncInvoke\fR will invoke them all; at each point it | |
378 | invokes the highest-priority (oldest) ready handler, repeating | |
379 | this over and over until there are no longer any ready handlers. | |
380 | ||
381 | .SH WARNING | |
382 | .PP | |
383 | It is almost always a bad idea for an asynchronous event | |
384 | handler to modify the interpreter's result or return a code different | |
385 | from its \fIcode\fR argument. | |
386 | This sort of behavior can disrupt the execution of scripts in | |
387 | subtle ways and result in bugs that are extremely difficult | |
388 | to track down. | |
389 | If an asynchronous event handler needs to evaluate Tcl scripts | |
390 | then it should first save the interpreter's result plus the values | |
391 | of the variables \fBerrorInfo\fR and \fBerrorCode\fR (this can | |
392 | be done, for example, by storing them in dynamic strings). | |
393 | When the asynchronous handler is finished it should restore | |
394 | the interpreter's result, \fBerrorInfo\fR, and \fBerrorCode\fR, | |
395 | and return the \fIcode\fR argument. | |
396 | ||
397 | .SH KEYWORDS | |
398 | asynchronous event, handler, signal |