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tclXtNotify.c

/*
 * tclXtNotify.c --
 *
 *    This file contains the notifier driver implementation for the Xt
 *    intrinsics.
 *
 * Copyright (c) 1997 by 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: tclXtNotify.c,v 1.9 2007/04/16 13:36:36 dkf Exp $
 */

#include <X11/Intrinsic.h>
#include "tclInt.h"

/*
 * This structure is used to keep track of the notifier info for a a
 * registered file.
 */

typedef struct FileHandler {
    int fd;
    int mask;                 /* Mask of desired events: TCL_READABLE,
                         * etc. */
    int readyMask;            /* Events that have been seen since the last
                         * time FileHandlerEventProc was called for
                         * this file. */
    XtInputId read;           /* Xt read callback handle. */
    XtInputId write;          /* Xt write callback handle. */
    XtInputId except;         /* Xt exception callback handle. */
    Tcl_FileProc *proc;       /* Procedure to call, in the style of
                         * Tcl_CreateFileHandler. */
    ClientData clientData;    /* Argument to pass to proc. */
    struct FileHandler *nextPtr;/* Next in list of all files we care about. */
} FileHandler;

/*
 * The following structure is what is added to the Tcl event queue when file
 * handlers are ready to fire.
 */

typedef struct FileHandlerEvent {
    Tcl_Event header;         /* Information that is standard for all
                         * events. */
    int fd;             /* File descriptor that is ready. Used to find
                         * the FileHandler structure for the file
                         * (can't point directly to the FileHandler
                         * structure because it could go away while
                         * the event is queued). */
} FileHandlerEvent;

/*
 * The following static structure contains the state information for the Xt
 * based implementation of the Tcl notifier.
 */

static struct NotifierState {
    XtAppContext appContext;  /* The context used by the Xt notifier. Can be
                         * set with TclSetAppContext. */
    int appContextCreated;    /* Was it created by us? */
    XtIntervalId currentTimeout;/* Handle of current timer. */
    FileHandler *firstFileHandlerPtr;
                        /* Pointer to head of file handler list. */
} notifier;

/*
 * The following static indicates whether this module has been initialized.
 */

static int initialized = 0;

/*
 * Static routines defined in this file.
 */

static int        FileHandlerEventProc(Tcl_Event *evPtr, int flags);
static void       FileProc(caddr_t clientData, int *source,
                      XtInputId *id);
void              InitNotifier(void);
static void       NotifierExitHandler(ClientData clientData);
static void       TimerProc(caddr_t clientData, XtIntervalId *id);
static void       CreateFileHandler(int fd, int mask,
                        Tcl_FileProc * proc, ClientData clientData);
static void       DeleteFileHandler(int fd);
static void       SetTimer(Tcl_Time * timePtr);
static int        WaitForEvent(Tcl_Time * timePtr);

/*
 * Functions defined in this file for use by users of the Xt Notifier:
 */

EXTERN XtAppContext     TclSetAppContext(XtAppContext ctx);

/*
 *----------------------------------------------------------------------
 *
 * TclSetAppContext --
 *
 *    Set the notifier application context.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Sets the application context used by the notifier. Panics if the
 *    context is already set when called.
 *
 *----------------------------------------------------------------------
 */

XtAppContext
TclSetAppContext(
    XtAppContext appContext)
{
    if (!initialized) {
      InitNotifier();
    }

    /*
     * If we already have a context we check whether we were asked to set a
     * new context. If so, we panic because we try to prevent switching
     * contexts by mistake. Otherwise, we return the one we have.
     */

    if (notifier.appContext != NULL) {
      if (appContext != NULL) {
          /*
           * We already have a context. We do not allow switching contexts
           * after initialization, so we panic.
           */

          Tcl_Panic("TclSetAppContext:  multiple application contexts");
      }
    } else {
      /*
       * If we get here we have not yet gotten a context, so either create
       * one or use the one supplied by our caller.
       */

      if (appContext == NULL) {
          /*
           * We must create a new context and tell our caller what it is, so
           * she can use it too.
           */

          notifier.appContext = XtCreateApplicationContext();
          notifier.appContextCreated = 1;
      } else {
          /*
           * Otherwise we remember the context that our caller gave us and
           * use it.
           */

          notifier.appContextCreated = 0;
          notifier.appContext = appContext;
      }
    }

    return notifier.appContext;
}

/*
 *----------------------------------------------------------------------
 *
 * InitNotifier --
 *
 *    Initializes the notifier state.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Creates a new exit handler.
 *
 *----------------------------------------------------------------------
 */

void
InitNotifier(void)
{
    Tcl_NotifierProcs notifier;

    /*
     * Only reinitialize if we are not in exit handling. The notifier can get
     * reinitialized after its own exit handler has run, because of exit
     * handlers for the I/O and timer sub-systems (order dependency).
     */

    if (TclInExit()) {
      return;
    }

    notifier.createFileHandlerProc = CreateFileHandler;
    notifier.deleteFileHandlerProc = DeleteFileHandler;
    notifier.setTimerProc = SetTimer;
    notifier.waitForEventProc = WaitForEvent;
    Tcl_SetNotifier(&notifier);

    /*
     * DO NOT create the application context yet; doing so would prevent
     * external applications from setting it for us to their own ones.
     */

    initialized = 1;
    memset(&notifier, 0, sizeof(notifier));
    Tcl_CreateExitHandler(NotifierExitHandler, NULL);
}

/*
 *----------------------------------------------------------------------
 *
 * NotifierExitHandler --
 *
 *    This function is called to cleanup the notifier state before Tcl is
 *    unloaded.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Destroys the notifier window.
 *
 *----------------------------------------------------------------------
 */

static void
NotifierExitHandler(
    ClientData clientData)    /* Not used. */
{
    if (notifier.currentTimeout != 0) {
      XtRemoveTimeOut(notifier.currentTimeout);
    }
    for (; notifier.firstFileHandlerPtr != NULL; ) {
      Tcl_DeleteFileHandler(notifier.firstFileHandlerPtr->fd);
    }
    if (notifier.appContextCreated) {
      XtDestroyApplicationContext(notifier.appContext);
      notifier.appContextCreated = 0;
      notifier.appContext = NULL;
    }
    initialized = 0;
}

/*
 *----------------------------------------------------------------------
 *
 * SetTimer --
 *
 *    This procedure sets the current notifier timeout value.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Replaces any previous timer.
 *
 *----------------------------------------------------------------------
 */

static void
SetTimer(
    Tcl_Time *timePtr)        /* Timeout value, may be NULL. */
{
    long timeout;

    if (!initialized) {
      InitNotifier();
    }

    TclSetAppContext(NULL);
    if (notifier.currentTimeout != 0) {
      XtRemoveTimeOut(notifier.currentTimeout);
    }
    if (timePtr) {
      timeout = timePtr->sec * 1000 + timePtr->usec / 1000;
      notifier.currentTimeout = XtAppAddTimeOut(notifier.appContext,
            (unsigned long) timeout, TimerProc, NULL);
    } else {
      notifier.currentTimeout = 0;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TimerProc --
 *
 *    This procedure is the XtTimerCallbackProc used to handle timeouts.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Processes all queued events.
 *
 *----------------------------------------------------------------------
 */

static void
TimerProc(
    caddr_t data,       /* Not used. */
    XtIntervalId *id)
{
    if (*id != notifier.currentTimeout) {
      return;
    }
    notifier.currentTimeout = 0;

    Tcl_ServiceAll();
}

/*
 *----------------------------------------------------------------------
 *
 * CreateFileHandler --
 *
 *    This procedure registers a file handler with the Xt notifier.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Creates a new file handler structure and registers one or more input
 *    procedures with Xt.
 *
 *----------------------------------------------------------------------
 */

static void
CreateFileHandler(
    int fd,             /* Handle of stream to watch. */
    int mask,                 /* OR'ed combination of TCL_READABLE,
                         * TCL_WRITABLE, and TCL_EXCEPTION: indicates
                         * conditions under which proc should be
                         * called. */
    Tcl_FileProc *proc,       /* Procedure to call for each selected
                         * event. */
    ClientData clientData)    /* Arbitrary data to pass to proc. */
{
    FileHandler *filePtr;

    if (!initialized) {
      InitNotifier();
    }

    TclSetAppContext(NULL);

    for (filePtr = notifier.firstFileHandlerPtr; filePtr != NULL;
          filePtr = filePtr->nextPtr) {
      if (filePtr->fd == fd) {
          break;
      }
    }
    if (filePtr == NULL) {
      filePtr = (FileHandler*) ckalloc(sizeof(FileHandler));
      filePtr->fd = fd;
      filePtr->read = 0;
      filePtr->write = 0;
      filePtr->except = 0;
      filePtr->readyMask = 0;
      filePtr->mask = 0;
      filePtr->nextPtr = notifier.firstFileHandlerPtr;
      notifier.firstFileHandlerPtr = filePtr;
    }
    filePtr->proc = proc;
    filePtr->clientData = clientData;

    /*
     * Register the file with the Xt notifier, if it hasn't been done yet.
     */

    if (mask & TCL_READABLE) {
      if (!(filePtr->mask & TCL_READABLE)) {
          filePtr->read = XtAppAddInput(notifier.appContext, fd,
                XtInputReadMask, FileProc, filePtr);
      }
    } else {
      if (filePtr->mask & TCL_READABLE) {
          XtRemoveInput(filePtr->read);
      }
    }
    if (mask & TCL_WRITABLE) {
      if (!(filePtr->mask & TCL_WRITABLE)) {
          filePtr->write = XtAppAddInput(notifier.appContext, fd,
                XtInputWriteMask, FileProc, filePtr);
      }
    } else {
      if (filePtr->mask & TCL_WRITABLE) {
          XtRemoveInput(filePtr->write);
      }
    }
    if (mask & TCL_EXCEPTION) {
      if (!(filePtr->mask & TCL_EXCEPTION)) {
          filePtr->except = XtAppAddInput(notifier.appContext, fd,
                XtInputExceptMask, FileProc, filePtr);
      }
    } else {
      if (filePtr->mask & TCL_EXCEPTION) {
          XtRemoveInput(filePtr->except);
      }
    }
    filePtr->mask = mask;
}

/*
 *----------------------------------------------------------------------
 *
 * DeleteFileHandler --
 *
 *    Cancel a previously-arranged callback arrangement for a file.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    If a callback was previously registered on file, remove it.
 *
 *----------------------------------------------------------------------
 */

static void
DeleteFileHandler(
    int fd)             /* Stream id for which to remove callback
                         * procedure. */
{
    FileHandler *filePtr, *prevPtr;

    if (!initialized) {
      InitNotifier();
    }

    TclSetAppContext(NULL);

    /*
     * Find the entry for the given file (and return if there isn't one).
     */

    for (prevPtr = NULL, filePtr = notifier.firstFileHandlerPtr; ;
          prevPtr = filePtr, filePtr = filePtr->nextPtr) {
      if (filePtr == NULL) {
          return;
      }
      if (filePtr->fd == fd) {
          break;
      }
    }

    /*
     * Clean up information in the callback record.
     */

    if (prevPtr == NULL) {
      notifier.firstFileHandlerPtr = filePtr->nextPtr;
    } else {
      prevPtr->nextPtr = filePtr->nextPtr;
    }
    if (filePtr->mask & TCL_READABLE) {
      XtRemoveInput(filePtr->read);
    }
    if (filePtr->mask & TCL_WRITABLE) {
      XtRemoveInput(filePtr->write);
    }
    if (filePtr->mask & TCL_EXCEPTION) {
      XtRemoveInput(filePtr->except);
    }
    ckfree((char *) filePtr);
}

/*
 *----------------------------------------------------------------------
 *
 * FileProc --
 *
 *    These procedures are called by Xt when a file becomes readable,
 *    writable, or has an exception.
 *
 * Results:
 *    None.
 *
 * Side effects:
 *    Makes an entry on the Tcl event queue if the event is interesting.
 *
 *----------------------------------------------------------------------
 */

static void
FileProc(
    caddr_t clientData,
    int *fd,
    XtInputId *id)
{
    FileHandler *filePtr = (FileHandler *)clientData;
    FileHandlerEvent *fileEvPtr;
    int mask = 0;

    /*
     * Determine which event happened.
     */

    if (*id == filePtr->read) {
      mask = TCL_READABLE;
    } else if (*id == filePtr->write) {
      mask = TCL_WRITABLE;
    } else if (*id == filePtr->except) {
      mask = TCL_EXCEPTION;
    }

    /*
     * Ignore unwanted or duplicate events.
     */

    if (!(filePtr->mask & mask) || (filePtr->readyMask & mask)) {
      return;
    }

    /*
     * This is an interesting event, so put it onto the event queue.
     */

    filePtr->readyMask |= mask;
    fileEvPtr = (FileHandlerEvent *) ckalloc(sizeof(FileHandlerEvent));
    fileEvPtr->header.proc = FileHandlerEventProc;
    fileEvPtr->fd = filePtr->fd;
    Tcl_QueueEvent((Tcl_Event *) fileEvPtr, TCL_QUEUE_TAIL);

    /*
     * Process events on the Tcl event queue before returning to Xt.
     */

    Tcl_ServiceAll();
}

/*
 *----------------------------------------------------------------------
 *
 * FileHandlerEventProc --
 *
 *    This procedure is called by Tcl_ServiceEvent when a file event reaches
 *    the front of the event queue. This procedure is responsible for
 *    actually handling the event by invoking the callback for the file
 *    handler.
 *
 * Results:
 *    Returns 1 if the event was handled, meaning it should be removed from
 *    the queue. Returns 0 if the event was not handled, meaning it should
 *    stay on the queue. The only time the event isn't handled is if the
 *    TCL_FILE_EVENTS flag bit isn't set.
 *
 * Side effects:
 *    Whatever the file handler's callback procedure does.
 *
 *----------------------------------------------------------------------
 */

static int
FileHandlerEventProc(
    Tcl_Event *evPtr,         /* Event to service. */
    int flags)                /* Flags that indicate what events to handle,
                         * such as TCL_FILE_EVENTS. */
{
    FileHandler *filePtr;
    FileHandlerEvent *fileEvPtr = (FileHandlerEvent *) evPtr;
    int mask;

    if (!(flags & TCL_FILE_EVENTS)) {
      return 0;
    }

    /*
     * Search through the file handlers to find the one whose handle matches
     * the event. We do this rather than keeping a pointer to the file handler
     * directly in the event, so that the handler can be deleted while the
     * event is queued without leaving a dangling pointer.
     */

    for (filePtr = notifier.firstFileHandlerPtr; filePtr != NULL;
          filePtr = filePtr->nextPtr) {
      if (filePtr->fd != fileEvPtr->fd) {
          continue;
      }

      /*
       * The code is tricky for two reasons:
       * 1. The file handler's desired events could have changed since the
       *    time when the event was queued, so AND the ready mask with the
       *    desired mask.
       * 2. The file could have been closed and re-opened since the time
       *    when the event was queued. This is why the ready mask is stored
       *    in the file handler rather than the queued event: it will be
       *    zeroed when a new file handler is created for the newly opened
       *    file.
       */

      mask = filePtr->readyMask & filePtr->mask;
      filePtr->readyMask = 0;
      if (mask != 0) {
          (*filePtr->proc)(filePtr->clientData, mask);
      }
      break;
    }
    return 1;
}

/*
 *----------------------------------------------------------------------
 *
 * WaitForEvent --
 *
 *    This function is called by Tcl_DoOneEvent to wait for new events on
 *    the message queue. If the block time is 0, then Tcl_WaitForEvent just
 *    polls without blocking.
 *
 * Results:
 *    Returns 1 if an event was found, else 0. This ensures that
 *    Tcl_DoOneEvent will return 1, even if the event is handled by non-Tcl
 *    code.
 *
 * Side effects:
 *    Queues file events that are detected by the select.
 *
 *----------------------------------------------------------------------
 */

static int
WaitForEvent(
    Tcl_Time *timePtr)        /* Maximum block time, or NULL. */
{
    int timeout;

    if (!initialized) {
      InitNotifier();
    }

    TclSetAppContext(NULL);

    if (timePtr) {
      timeout = timePtr->sec * 1000 + timePtr->usec / 1000;
      if (timeout == 0) {
          if (XtAppPending(notifier.appContext)) {
            goto process;
          } else {
            return 0;
          }
      } else {
          Tcl_SetTimer(timePtr);
      }
    }

  process:
    XtAppProcessEvent(notifier.appContext, XtIMAll);
    return 1;
}

/*
 * Local Variables:
 * mode: c
 * c-basic-offset: 4
 * fill-column: 78
 * End:
 */

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