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| 9 | '\" |
| 10 | '\" The definitions below are for supplemental macros used in Tcl/Tk |
| 11 | '\" manual entries. |
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| 71 | '\" RCS: @(#) $Id: man.macros,v 1.4 2000/08/25 06:18:32 ericm Exp $ |
| 72 | '\" |
| 73 | '\" # Set up traps and other miscellaneous stuff for Tcl/Tk man pages. |
| 74 | .if t .wh -1.3i ^B |
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| 77 | '\" # Start an argument description |
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| 107 | .. |
| 108 | .AS Tcl_Interp Tcl_CreateInterp in/out |
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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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| 226 | Command-Line Name: \\fB\\$1\\fR |
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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 |