source: trunk/tcl/tclAsync.c@ 7

/* 
 * tclAsync.c --
 *
 *      This file provides low-level support needed to invoke signal
 *      handlers in a safe way.  The code here doesn't actually handle
 *      signals, though.  This code is based on proposals made by
 *      Mark Diekhans and Don Libes.
 *
 * Copyright (c) 1993 The Regents of the University of California.
 * Copyright (c) 1994 Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution
 * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * RCS: @(#) $Id: tclAsync.c,v 1.1 2008-06-04 13:58:03 demin Exp $
 */

#include "tclInt.h"

/*
 * One of the following structures exists for each asynchronous
 * handler:
 */

typedef struct AsyncHandler {
    int ready;                          /* Non-zero means this handler should
                                         * be invoked in the next call to
                                         * Tcl_AsyncInvoke. */
    struct AsyncHandler *nextPtr;       /* Next in list of all handlers for
                                         * the process. */
    Tcl_AsyncProc *proc;                /* Procedure to call when handler
                                         * is invoked. */
    ClientData clientData;              /* Value to pass to handler when it
                                         * is invoked. */
} AsyncHandler;

/*
 * The variables below maintain a list of all existing handlers.
 */

static AsyncHandler *firstHandler;      /* First handler defined for process,
                                         * or NULL if none. */
static AsyncHandler *lastHandler;       /* Last handler or NULL. */

/*
 * The variable below is set to 1 whenever a handler becomes ready and
 * it is cleared to zero whenever Tcl_AsyncInvoke is called.  It can be
 * checked elsewhere in the application by calling Tcl_AsyncReady to see
 * if Tcl_AsyncInvoke should be invoked.
 */

static int asyncReady = 0;

/*
 * The variable below indicates whether Tcl_AsyncInvoke is currently
 * working.  If so then we won't set asyncReady again until
 * Tcl_AsyncInvoke returns.
 */

static int asyncActive = 0;


/*
 *----------------------------------------------------------------------
 *
 * Tcl_AsyncCreate --
 *
 *      This procedure creates the data structures for an asynchronous
 *      handler, so that no memory has to be allocated when the handler
 *      is activated.
 *
 * Results:
 *      The return value is a token for the handler, which can be used
 *      to activate it later on.
 *
 * Side effects:
 *      Information about the handler is recorded.
 *
 *----------------------------------------------------------------------
 */

Tcl_AsyncHandler
Tcl_AsyncCreate(proc, clientData)
    Tcl_AsyncProc *proc;                /* Procedure to call when handler
                                         * is invoked. */
    ClientData clientData;              /* Argument to pass to handler. */
{
    AsyncHandler *asyncPtr;

    asyncPtr = (AsyncHandler *) ckalloc(sizeof(AsyncHandler));
    asyncPtr->ready = 0;
    asyncPtr->nextPtr = NULL;
    asyncPtr->proc = proc;
    asyncPtr->clientData = clientData;
    if (firstHandler == NULL) {
        firstHandler = asyncPtr;
    } else {
        lastHandler->nextPtr = asyncPtr;
    }
    lastHandler = asyncPtr;
    return (Tcl_AsyncHandler) asyncPtr;
}


/*
 *----------------------------------------------------------------------
 *
 * Tcl_AsyncMark --
 *
 *      This procedure is called to request that an asynchronous handler
 *      be invoked as soon as possible.  It's typically called from
 *      an interrupt handler, where it isn't safe to do anything that
 *      depends on or modifies application state.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      The handler gets marked for invocation later.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_AsyncMark(async)
    Tcl_AsyncHandler async;             /* Token for handler. */
{
    ((AsyncHandler *) async)->ready = 1;
    if (!asyncActive) {
        asyncReady = 1;
    }
}


/*
 *----------------------------------------------------------------------
 *
 * Tcl_AsyncInvoke --
 *
 *      This procedure is called at a "safe" time at background level
 *      to invoke any active asynchronous handlers.
 *
 * Results:
 *      The return value is a normal Tcl result, which is intended to
 *      replace the code argument as the current completion code for
 *      interp.
 *
 * Side effects:
 *      Depends on the handlers that are active.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_AsyncInvoke(interp, code)
    Tcl_Interp *interp;                 /* If invoked from Tcl_Eval just after
                                         * completing a command, points to
                                         * interpreter.  Otherwise it is
                                         * NULL. */
    int code;                           /* If interp is non-NULL, this gives
                                         * completion code from command that
                                         * just completed. */
{
    AsyncHandler *asyncPtr;

    if (asyncReady == 0) {
        return code;
    }
    asyncReady = 0;
    asyncActive = 1;
    if (interp == NULL) {
        code = 0;
    }

    /*
     * Make one or more passes over the list of handlers, invoking
     * at most one handler in each pass.  After invoking a handler,
     * go back to the start of the list again so that (a) if a new
     * higher-priority handler gets marked while executing a lower
     * priority handler, we execute the higher-priority handler
     * next, and (b) if a handler gets deleted during the execution
     * of a handler, then the list structure may change so it isn't
     * safe to continue down the list anyway.
     */

    while (1) {
        for (asyncPtr = firstHandler; asyncPtr != NULL;
                asyncPtr = asyncPtr->nextPtr) {
            if (asyncPtr->ready) {
                break;
            }
        }
        if (asyncPtr == NULL) {
            break;
        }
        asyncPtr->ready = 0;
        code = (*asyncPtr->proc)(asyncPtr->clientData, interp, code);
    }
    asyncActive = 0;
    return code;
}


/*
 *----------------------------------------------------------------------
 *
 * Tcl_AsyncDelete --
 *
 *      Frees up all the state for an asynchronous handler.  The handler
 *      should never be used again.
 *
 * Results:
 *      None.
 *
 * Side effects:
 *      The state associated with the handler is deleted.
 *
 *----------------------------------------------------------------------
 */

void
Tcl_AsyncDelete(async)
    Tcl_AsyncHandler async;             /* Token for handler to delete. */
{
    AsyncHandler *asyncPtr = (AsyncHandler *) async;
    AsyncHandler *prevPtr;

    if (firstHandler == asyncPtr) {
        firstHandler = asyncPtr->nextPtr;
        if (firstHandler == NULL) {
            lastHandler = NULL;
        }
    } else {
        prevPtr = firstHandler;
        while (prevPtr->nextPtr != asyncPtr) {
            prevPtr = prevPtr->nextPtr;
        }
        prevPtr->nextPtr = asyncPtr->nextPtr;
        if (lastHandler == asyncPtr) {
            lastHandler = prevPtr;
        }
    }
    ckfree((char *) asyncPtr);
}


/*
 *----------------------------------------------------------------------
 *
 * Tcl_AsyncReady --
 *
 *      This procedure can be used to tell whether Tcl_AsyncInvoke
 *      needs to be called.  This procedure is the external interface
 *      for checking the internal asyncReady variable.
 *
 * Results:
 *      The return value is 1 whenever a handler is ready and is 0
 *      when no handlers are ready.
 *
 * Side effects:
 *      None.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_AsyncReady()
{
    return asyncReady;
}