Explorer uses three controlling interfaces or “wrappers” to mediate between the module's user function and the rest of the system. They are the Module Control Wrapper (MCW), the Module Data Wrapper (MDW), and the Generic Wrapper. The relationship between wrappers and user or computational function is shown in Figure 9-2.

Figure 9-2. The Module Structure

In general, when you build a module, the Module Builder writes code for the Module Data Wrapper and generates a linkage to a default Module Control Wrapper (MCW), or an X Windows MCW if so selected. You make these choices using the Build Options window.

To display the Build Options window, select “Options” from the Build menu on the Module Builder window. The Build Options window offers you options for expanding individual control over the interface between the user function and Explorer.

This example shows how an X drawing area can be used as an input mechanism. It places a Motif button in an X drawing area and reports whenever the button is pressed. The code is in /usr/explorer/src/MWGcode/Advanced/C/XDrawInput.c.

---

Note: It is not possible to write this module in Fortran.

---

#include <X11/Intrinsic.h>
#include <X11/Xm/PushB.h>

#include <cx/XtArea.h>

void xcallback(Widget w, void *client)
{
 printf(“button pressed\n”);
}

void xwidget(long window)
{
 static int first = 1;
 static Widget top;

 Widget button;

 /*
 * Do initialization stuff
 */
 if (first) {
    first = 0;

    /*
     * Get a Xt form and put a button on it
     */
    top = cxXtAreaInitialize();
    button = XtVaCreateManagedWidget(“button”,
       xmPushButtonWidgetClass, top,
        XmNleftAttachment, XmATTACH_FORM,
        XmNrightAttachment, XmATTACH_FORM,
        XmNtopAttachment, XmATTACH_FORM,
        XmNbottomAttachment, XmATTACH_FORM,
        NULL);

   /*
    * Add a callback then attach the form to the window
    */
   XtAddCallback(button, XmNactivateCallback,
    (XtCallbackProc) xcallback, (XtPointer) NULL);

   cxXtAreaAttach(top, window);
 }
 cxXtAreaResize(top, window);
}

#include <stdio.h>

/* X includes */
#include <X11/Intrinsic.h>
#include <X11/Xm/Xm.h>
#include <X11/Xirisw/GlxMDraw.h>

/* GL includes */
#include <gl/gl.h>

/* Explorer includes */
#include <cx/PortAccess.h>
#include <cx/DataAccess.h>
#include <cx/UserFuncs.h>
#include <cx/XtArea.h>

Widget top;          /* top level form widget */

/* 
 * Widget action routine 
 */
void xaction(void *client, XEvent *ev)
{
 float    p[2];  /* temporary storage for coordinates */
 short    ysize; /* height of GLX widget */
 switch (ev->type) {
 case ButtonPress:
     /*
     *IMPORTANT NOTE: X origin is *upper* left;
     *GL origin is *lower* left.
     */
     XtVaGetValues(top, XmNheight, &ysize, NULL);
     printf(“button pressed at %d, % d\n”,
       ev->xbutton.x, ysize - 1 - ev->xbutton.y);
     break;
 case Expose:
     /* some sample GL stuff
      */
      reshapeviewport();
      cpack(0x00b070a0);
      clear();

      perspective(400, 1.0, 0.5, 5.0);
      translate(0.0, 0.0, -4.0);
     cpack(0xffffffff);
     bgnclosedline();
     p[0] = 0.0;	
     p[1] = 0.0;	
     v2f(p);
     p[0] = 1.0;	
     p[1] = 1.0;	
     v2f(p);
     p[0] = 1.0;	
     p[1] = -1.0;	
     v2f(p);
     p[0] = -1.0;	
     p[1] = -1.0;	
     v2f(p);
     p[0] = -1.0;	
     p[1] = 1.0;	
     v2f(p);
    endclosedline();
    swapbuffers();
    break
    }
}
/*
 * Module initialization routine
 *
 * This routine must be listed as the “initialization” hook function
 */
void xex2_init()
{
    long            wid;           /* window id from UI */
    Widget          da;            /* drawing area widget */
    XtTranslations  translations;  /* X translations structure */

    static XtActionsRec actions[] ={/* X actions record */
                                “xaction”,(XtActionProc) xaction
   };
  static GLXconfig config[] ={/* GL configuration */ 
                              GLX_NORMAL, GLX_RGB, TRUE,
                              GLX_NORMAL, GLX_DOUBLE, TRUE,
                              GLX_NORMAL, GLX_ZSIZE, GLX_NOCONFIG,
                               0, 0, 0
  };

  /*
  * initialize an Xt area, get an empty form widget 
  */
  top = cxXtAreaInitialize();

  /*
   * get the UI drawing area widget id 
   */
   wid = cxParamLongGet((cxParameter *) cxInputDataGet(
   cxInputPortOpen(“window”)));

   /*
   * define some actions and translations for our widget 
   */
   XtAddActions(actions, XtNumber(actions));
   translations = XtParseTranslationTable(
      “ < BtnDown > : xaction()\n\
        < Expose > : xaction()”);

   /*
   * put a drawing area widget in the form 
   */
    da = XtVaCreateManagedWidget(“da”, glxMDrawWidgetClass, top,
                                 GlxNglxConfig, config,
                                 XmNtranslations, translations,
                                 XmNleftAttachment,       XmATTACH_FORM,
                                 XmNtopAttachment, XmATTACH_FORM,
                                 XmNrightAttachment, XmATTACH_FORM,
                                     XmNbottomAttachment, XmATTACH_FORM,
                                     NULL);

   /*
    * attach the form to the drawing area window 
    */
    cxXtAreaAttach(top, wid);
}
/*
* Module execution function
 *
 */
long       xex2()
{
     int   windowPort;  /* port number of window parameter */
     long  wid;         /* window id from UI */

     /*
      * get window port number and the widget ID of the drawing area
      */
      windowPort = cxInputPortOpen(“window”);
      wid = cxParamLongGet((cxParameter * )cxInputDataGet(
      cxInputPortOpen(“window”)));

      /*
       * resize the form widget to the UI drawing area size
       */
       cxXtAreaResize(top, wid);

       return 0;
}

c redraw procedure
         subroutine refresh(widget,client)
         integer widget
         integer client
         real p(2)

c configure the viewport
         call reshap()

c clear the screen
         call cpack(11563168)
         call clear()

c do some example GL stuff
         call perspe(400,1.0,0.5,5.0)
         call transl(0.0,0.0,-4.0)
         call cpack(-1)
         call bgnclo()

         p(1) = 0.0
         p(2) = 0.0
         call v2f(p)

         p(1) = 1.0
         p(2) = 1.0
         call v2f(p)

         p(1) = 1.0
         p(2) = -1.0
         call v2f(p)

         p(1) = -1.0
         p(2) = -1.0
         call v2f(p)

         p(1) = -1.0
         p(2) = 1.0
         call v2f(p)

         call endclo()
         call swapbu()

         return
         end

c input procedure
         subroutine input(widget,client,info)

         integer widget
         integer client
         integer info(5)
         integer xevptr
         integer xev(32)
         pointer (xevptr,xev)

c get the pointer to the X event
c   xev will now point to the XEvent structure.  Be *very* careful extracting
c   fields from this C struct.  This is definitely not portable code.
         xevptr = info(2)

c switch on the kind of event
c   Event numbers may be found in /usr/include/X.h.  Here are a few examples:
c       KeyPress                2
c       KeyRelease              3
c       ButtonPress             4
c       ButtonRelease           5

         if ( xev(1) .eq. 4 ) then

c IMPORTANT NOTE: X origin is *upper* left;
c GL origin is *lower* left.
                type *,'button pressed at ',xev(9),', ',xev(10)
         endif

         return
         end

c user function
         SUBROUTINE FGL ( WIN )

         INTEGER WIN

C
C Complete the user function by adding subprogram lines here.
C 
         integer widget
         integer config(12)
         logical first

         integer cxXtGLAreaInitialize

#        include “cx/XtGLArea.inc”

c NOTE -- the redraw and input procedures MUST be declared external
         external refresh
         external input
         common widget
         data first/.true./

         if ( first ) then
c first time initialization
                 first = .false.

c set up the GL configuration information
                 config(1) = GLX_NORMAL
                 config(2) = GLX_RGB
                 config(3) = 1
                 config(4) = GLX_NORMAL
                 config(5) = GLX_DOUBLE
                 config(6) = 1
                 config(7) = GLX_NORMAL
                 config(8) = GLX_ZSIZE
                 config(9) = GLX_NOCONFIG
                 config(10) = 0
                 config(11) = 0
                 config(12) = 0

c create the GL area
                 widget = cxXtGLAreaInitialize(WIN,config)

c register the redraw and input procedures with the widget
                 call cxXtGLAreaRedraw(widget,refresh,0)
                 call cxXtAreaCallbackAdd(widget,'inputCallback',input,0)
         endif
 
c match the GL area size with the window size
         call cxXtAreaResize(widget,WIN)

         RETURN
         END

 * This program creates a GL window and draws inside it.
 *
 * In order to link this code in a module, the proper set of geometry
 * and X Window System libraries must be defined in the user Imakefile
 */

#include <X11/Intrinsic.h>
#include <gl/glws.h>

#include <cx/XtArea.h>
#include <cx/XtGLArea.h>
/*
 * Redraw procedure
 */
void      refresh(void *w, void *client)
{

     float     p[2];				                    /* coordinate vector */

    /*
    * Configure the viewport and clear the display
    */
    reshapeviewport();
    cpack(0x00b070a0);
    clear()
    /*
    * Now do some sample GL stuff
    */
    perspective(400, 1.0, 0.5, 5.0);
    translate(0.0, 0.0, -4.0);
    cpack(0xffffffff);
    bgnclosedline();
    p[0] = 0.0; 	
    p[1] = 0.0; 		
    v2f(p);
    p[0] = 1.0; 	
    p[1] = 1.0; 		
    v2f(p);
    p[0] = 1.0; 	
    p[1] = -1.0; 		
    v2f(p);
    p[0] = -1.0; 	
    p[1] = -1.0; 		
    v2f(p);
    p[0] = -1.0; 	
    p[1] = 1.0; 		
    v2f(p);
    endclosedline();
    swapbuffers();
}
#include <cx/DataTypes.h>

#ifdef __cplusplus
extern “C” {
#endif
/*
 * User function
 */
void cgl ( long win )
{
     static first = 1;
    /* GLX configuration information */
    static GLXconfig config[] ={ 
      GLX_NORMAL, GLX_RGB, TRUE,
      GLX_NORMAL, GLX_DOUBLE, TRUE,
      GLX_NORMAL, GLX_ZSIZE, GLX_NOCONFIG,
      0, 0, 0
    };
    static Widget widget;

    /*
    * First time, do initialization
    */
    if (first) {
     first = 0;

    /*
     * Create the GL area and register the redraw proc
     */
      widget = cxXtGLAreaInitialize(win, config);
      cxXtGLAreaRedraw(widget, refresh, 0);
    }

    /*
    * Match the GL area size with user interface window size
    */
    cxXtAreaResize(widget, win);
}

#ifdef __cplusplus
}
#endif

Fortran Version:

c c This example creates a GL window and draws inside it. c c redraw procedure subroutine refresh(widget,client) integer widget integer client real p(2) c configure the viewport call reshap() c clear the screen call cpack(11563168) call clear() c do some example GL stuff call perspe(400,1.0,0.5,5.0) call transl(0.0,0.0,-4.0) call cpack(-1) call bgnclo() p(1) = 0.0 p(2) = 0.0 call v2f(p) p(1) = 1.0 p(2) = 1.0 call v2f(p) p(1) = 1.0 p(2) = -1.0 call v2f(p) p(1) = -1.0 p(2) = -1.0 call v2f(p) p(1) = -1.0 p(2) = 1.0 call v2f(p) call endclo() call swapbu() return end c user function subroutine fgl ( win ) integer win C C Complete the user function by adding subprogram lines here. C integer widget integer config(12) logical first integer cxXtGLAreaInitialize include “/usr/explorer/include/cx/XtGLArea.inc” c NOTE -- the redraw procedure MUST be declared external external refresh common widget data first/.true./ if ( first ) then c first time initialization first = .false. c set up the GL configuration information config(1) = GLX_NORMAL config(2) = GLX_RGB config(3) = 1 config(4) = GLX_NORMAL config(5) = GLX_DOUBLE config(6) = 1 config(7) = GLX_NORMAL config(8) = GLX_ZSIZE config(9) = GLX_NOCONFIG config(10) = 0 config(11) = 0 config(12) = 0 c create the GL area widget = cxXtGLAreaInitialize(win,config) c register the redraw procedure with the widget call cxXtGLAreaRedraw(widget,refresh,0) endif c match the gl area size with the window size call cxXtAreaResize(widget,win) return end

Figure 9-3 shows what the sample output from this module looks like.

Figure 9-3. Output from the XGLArea Routine

A combination module determines its actions in two ways. It can:

Both AddImg and XorImg have module resource files that describe their control panels and ports. In addition, on the Build Options menu, AddImg has “Alternate Executable” selected, with the name XorImg displayed in the executable name field. The XorImg module does not have “Alternate Executable” selected, so its name field is identical to the module name. it is clear that both AddImg and XorImg share the XorImg executable.

When the modules are built, the XorImg Makefile rules cause the XorImg executable to be compiled, linked, and installed along with XorImg.mres. The rules for AddImg cause only its module resources file to be installed, thus referring to the XorImg binary. When either module is started, the same executable is run. Enough information is provided to the XorImg binary that it can determined whether it was invoked as AddImg or XorImg, and, consequently, which set of functionality to provide.

The XorImg user function includes a call to the API routine cxModuleNameGet, which returns the name of the module that was invoked: in this case, AddImg or XorImg. The user function then compares the name to a table of known operations to determine whether to add or xor two images. The module can also use this name to determine its expected port names and to access its port data.

The DataScribe modules provide another example of the use of alternate executables. Each customized DataScribe module is simply a module resource file that expects an input script and knows which set of ports to query, based on the contents of the script. Every DataScribe module refers to the generic DataScribe module for its executable. The DataScribe module uses the input script, not cxModuleNameGet, to direct its activities, which are to interpret the input script and carry out specific actions on data files or Explorer ports.

An ordinary module, called MyModule for example, can use an executable name derived from its mres file, MyMod.mres. But some modules, notably the ImageVision Library^™ modules, refer to a different executable. Since many modules can refer to a single executable, those modules need not build the executable; some other similarly named module does that. For example, XorImg is the module that builds the executable XorImg; all the other ImageVision Library modules refer to it.

The “Alternate Executable” item in the Build Options window of the Module Builder lets you:

In the case of a combined executable, each module has its own module resources file, but only one of the modules creates and installs an executable. The executable is then responsible for determining which operation to invoke upon firing.

There are four API subroutines you can use when writing a loop controller module: cxLoopBreak, cxLoopControlArc, cxLoopCtlr, and cxLoopIteration. The three routines, cxLoopCtlr, cxLoopControlArc, and cxLoopIteration, are Boolean queries that deal respectively with loop controller status of the module, control arc status of a connection, and looping, as opposed to non-looping, invocation of an iteration. You can use these calls to get information about the actions and state of a loop controller module.

The cxLoopBreak routine halts a current loop iteration, as well as marking all pending iterations for cancellation by the loop controller. If the controller puts out “end-of-loop” data, those datasets should be assigned to the output ports when cxLoopBreak is called, as the user function will not be called again for that loop iteration. In programming a loop controller module, you must use the API routine cxLoopBreak to terminate iteration of a loop. This causes the MCW to cancel all pending iterations of the loop and return the module to a quiescent state.

You may also terminate a loop by sending out a sync frame, which is a frame with no new data, on the looping outputs. You must take care here, as the Map Editor user might wire a loop on ports you did not expect to be used, causing the module not to terminate the loop. It is safest to use cxLoopBreak in all cases.

The While and Repeat loop controller modules simply examine the condition for the loop, which is a parameter value, and copies a pointer over from the input to the output port. These are “typeless” modules which have cxGeneric input and output ports, and do not interrogate their generic inputs.

You can copy the modulename.mres file of these modules and modify each one slightly to create loop controllers that pass additional data sets through. Just rename the module and augment the port list.

While module has the ports listed in Table 9-2:

Substitute your own name for the “Value N” part of the port name. The module must match initial/final and loop in/loop out values. It can do this by finding the keywords “Initial”, “Final”, “LoopIn” and “LoopOut” on the port names.

The cxGeneric data type is found on input and output ports in the generic loop controller modules, which are For, While, Repeat, and Trigger. You can wire any port types into or out of a cxGeneric port.

The purpose of cxGeneric is to allow passage of all data types through a module. It is actually more of an encapsulation system than a true type, since it does not operate on the data at all.

There are two forms of the calling sequence, one used in the initialization and removal hook functions, and one used in the connection and disconnection hook functions.

For the latter, the MCW passes the name of the affected port (portName) and an integer that identifies that particular connection (linkID). The linkID values are unique with respect to a given port and increase throughout a single Explorer session.

The calling sequence of each type of hook function is given below. You can give a hook function or subroutine any name you like; these are merely examples.

Creating a module:

The MCW calls this function when the module is created, before connections are made and parameters are delivered. Parameter values, particularly drawing area window IDs, are meaningless at this time.

Connecting input ports:

The MCW calls this function after the user has connected input portName to some output.

Hook functions are ordinary procedures, which you must write before the MCW can use them. The hook functions and user function must both have either C or Fortran linkage; mixing linkages is not permitted.

The easiest way to generate hook function prototypes is to define them in the Module Builder as follows:

Here are some points to note when you are writing a hook function.

---

Note: If you have old modules that define cxHookTable, you must remove this definition from your source code. If you do not, you will see a multiply-defined symbol. This may make debugging more difficult, and on machines such as the Sun, the module will not build.

---

Here are some examples of hook functions. This hook function initializes the Geometry Library for a module that requires it.

void myInitFunc()
{
 /*
 * Initialize the geometry library
 */

 cxGeoInit();
}

This is an example of a connection hook function.

void myConnectFunc( portName, linkID )
char *portName;
int linkID;
{
 /*
 * Save the association of port and linkID 
 */

 myLinkArray[linkID] = portName;
}

All modules are responsible for collectively managing the data in shared memory. One module creates data and sends it to other modules. When all the modules are finished with that data, the space it occupies must be reclaimed. Explorer uses reference counting to manage this process. With reference counting, a module does not need to know anything about which other modules use the data. It must simply perform certain bookkeeping actions on the data it references, so that the system knows when the data should be reclaimed.

Reference counting is essential when using shared memory, but the mechanism is also general enough to be used by a single process on private data. Thus, modules executing on a machine that does not support shared memory can still use the same code for managing data memory.

As long as every module does its bookkeeping correctly and consistently, there will be no memory leaks, and data will not be reclaimed while a module still refers to it.

---

Caution: The automatically generated Module Data Wrapper cannot completely recover if the shared memory arena becomes full. It is possible that, if there is not enough memory for the computational function or for the MDW itself, the MDW may leak memory.

---

An integer is kept with each data object, to record the number of places where the data is used. When a module receives data, it increments the integer count to show that the data is being used in an additional place. When the module is finished with the data, it decrements the reference count. When the count becomes zero, the data is no longer needed and that module deletes the data.

For example, the module's input and output ports store data for the module, so they must manipulate the reference count. When the module puts data on the output port, the output port decrements the count of the old data on the port and increments the count of the new data. The output port retains use of the data so it can be sent to modules as they are connected to the port.

When a module receives new data, the input port decrements the count on the old data on that port and increments the count on the new data. The input port retains use of the data until it is replaced, which means the data is available every time the module fires, even if the data has not changed.

The API subroutines cxDataRefInc and cxDataRefDec are used to increment and decrement the reference count.

Explorer implements a less rigid version of reference counting than that defined above. Data objects are created with a reference count of 0 because nothing has claimed responsibility for decrementing the count. If the count on such an object is decremented immediately, it becomes –1. The object is deleted and no error is reported.

The default count of 0 simplifies coding of the user function cases. A data object is created and (usually) placed on the output port. The output port increments the count and assumes responsibility for maintaining the count, thus freeing the user function from that responsibility and allowing it to ignore the data. from the burden of If data objects were always created with a reference count of 1, then you would have to decrement the count of each object after placing it in the output port.

A user function may want to allocate a data object for temporary storage so that the same data can be output more than once. In this case, the user function does need to increment the count, ensuring that the data will persist as long as the user function needs it. When it is no longer required, the user function should decrement the count.

A module may have more than one reference to any data, so the value of the reference count may be greater than the number of modules using it. It is easier to code a module when you can allow it to have multiple references to the data, because the user function does not have to maintain exactly one reference count.

All Explorer system and user-defined data types are reference-counted. Data objects may contain references to other reference-counted objects. For example, the cxLattice and cxPyramid data types contain references to cxData, cxCoord, cxConnection, and cxLattice objects. The reference-counting scheme handles arbitrary sharing of Explorer data objects within other objects, just as data objects are shared between modules. For example, a cxData object can be contained in more than one cxLattice. Likewise, a cxLattice object can be contained in more than one cxPyramid and referenced by more than one module.

The shared memory arena is a fixed-size resource. It is at most 256 MB, and may not reach that size. Because it is stored in a memory-mapped file, its size is limited by the available disk space and the command line and configuration options that are specified when the user starts Explorer; therefore, it is possible for data memory allocation routines to fail, no matter how large the arena might be, because the arena size may exceed the amount of available memory.

The following examples show how to recover from allocation errors for some of the Explorer data types. They also illustrate some coding styles for recovery.

---

Note: These examples are in C only because they are meant to illustrate specific techniques, rather than provide reusable code.

---

cxParameter   *parm = NULL;
cxLattice     *lat1 = NULL;
cxLattice     *lat2 = NULL;

void memCleanup()
{
    cxDataRefDec( parm );
    cxDataRefDec( lat1 );
    cxDataRefDec( lat2 );
}

void userFunction()
{
    parm = cxParamNew( ... );
    if( cxDataAllocErrorGet() ) return; /* no cleanup required */
    lat1 = cxLatNew( ... );
    if( cxDataAllocErrorGet() ) {
        memCleanup();
        return;
    }
         lat2 = cxLatNew( ... );
         if( cxDataAllocErrorGet() ) {
             memCleanup();
             return;
         }
         .
         .
}

void userFunction()
{
         cxParameter         *parm = NULL;
         cxLattice           *lat1 = NULL;
         cxLattice           *lat2 = NULL;

         parm = cxParamNew( ... );
         if( cxDataAllocErrorGet() ) goto parm_Failed;
         lat1 = cxLatNew( ... );
         if( cxDataAllocErrorGet() ) goto lat1_Failed;
         lat2 = cxLatNew( ... );
         if( cxDataAllocErrorGet() ) goto lat2_Failed;
         .
         .
         /* normal return */
         return;

lat2_Failed:
     cxDataRefDec( lat1 );
lat1_Failed:
     cxDataRefDec( parm );
parm_Failed:
     return;
}

Example 3

The third example shows the memory for lattice data and coordinates allocated separately. Recovery becomes more complicated in this case. Once cxLatPtrSet stores data and coords into lat1, lat1 has reference counts on data and coords and is responsible for decrementing their counts.

---

Note: Do not decrement data or coords (although you can still use the pointers). Explorer has no way of tracking their values, and will not attempt to decrement the reference counts.

---

void userFunction() { cxLattice *lat1, *lat2; cxData *data; cxCoord *coords; lat1 = cxLatRootNew( ... ); if( cxDataAllocErrorGet() ) return; data = cxDataNew( ... ); if( cxDataAllocErrorGet() { cxDataRefDec( lat1 ); return; coords = cxCoordNew( ... ); if( cxDataAllocErrorGet() ) { cxDataRefDec( lat1 ); cxDataRefDec( data ); return; } /* cxLatPtrSet doesn't allocate memory */ cxLatPtrSet( lat1, data, NULL, coords, NULL ); lat2 = cxLatNew( ... ); if( cxDataAllocErrorGet() ) { cxDataRefDec( lat1 ); /* NOT data or coords */ return; { . . /* normal return */ return; }

void userFunction()
{
      cxPyramid     *pyr;
      cxLattice     *base, *layer, *other;
      cxConnection  *conn;

      base = cxLatNew( ... );
      if( cxDataAllocErrorGet() ) return;
      pyr = cxPyrNew( ... );
      if( cxDataAllocErrorGet() ) {
         cxDataRefDec( base );
         return;
         }
      cxPyrSet( pyr, base );          /* no allocation */

      layer = cxLatNew( ... );
         if( cxDataAllocErrorGet() ) {
             cxDataRefDec( pyr );     /* not base */
             return;
         }

       conn = cxConnNew( ... );
       if( cxDataAllocErrorGet() ) {
           cxDataRefDec( pyr );
           cxDataRefDec( layer );
           return;
         }

      cxPyrLayerSet( pyr, i, conn, layer );
      if( cxDataAllocErrorGet() ) {
          cxDataRefDec( pyr );         
          cxDataRefDec( layer );     /* layer and conn not in pyr */
           cxDataRefDec( conn );
        return;
         }
   other = cxLatNew( ... );
   if( cxDataAllocErrorGet() ) {
       cxDataRefDec( pyr );
       return;
         }
         .
         .
         /* normal return */
         return;
}

Example 5

The cxGeometry data type complicates error recovery even more, since it contains a buffer of transcribed geometry specification commands. Each geometry specification routine adds commands to this buffer, which may cause the buffer to be enlarged, so cxDataAllocErrorGet must be checked after each command. In addition, the actual buffer location is not associated with the geometry object while primitives are added, so the cxGeoBufferClose routine must be called before the geometry object can be reclaimed.

In this example, the module performs operations if the error flag is not set. It can then check the flag at key points and perform cleanup if required.

The buffer may be expanded more than once for each geometry specification command, so it may contain a partial command when the data allocation fails. The partial command may confuse downstream modules so seriously that the contents of the geometry must be thrown away.

Because the geometry interface is a delta protocol (only changes are sent), any cxGeoDelete command will be lost after the local data structures have been modified. The downstream modules will misinterpret future geometry inputs and will appear corrupted. The best way to recover is to disconnect and reconnect the geometry output that ran out of memory.

---

Note: cxGeoBufferClose should not be called twice on a cxGeometry object.

---

void userFunction() { cxGeometry *geo; geo = cxGeoNew(); if( cxDataAllocErrorGet() ) return; cxGeoBufferSelect( geo ); if( !cxDataAllocErrorGet() ) cxGeoRoot(); if( !cxDataAllocErrorGet() ) cxGeoDelete(); if( cxDataAllocErrorGet() ) goto cleanup_selected; cxGeoXformPush(); if( !cxDataAllocErrorGet() ) cxGeoLinesDefine( ... ); if( !cxDataAllocErrorGet() ) cxGeoColorAdd( ... ); if( !cxDataAllocErrorGet() ) cxGeoXformPop(); if( cxDataAllocErrorGet() ) goto cleanup_selected; cxGeoBufferClose( geo ); if( cxDataAllocErrorGet() ) goto cleanup: . . . /* normal return */ return; cleanup_selected: cxGeoBufferClose( geo ); cleanup: cxDataRefDec( geo ); return; }

The subroutine cxInputAdd registers an open UNIX file descriptor that the module will monitor. The file descriptor can reference any UNIX device on the system that has a file descriptor. The module can request that it be informed when the device is ready for reading or writing, or when an exception condition exists. When one of these conditions is met, the Module Control Wrapper calls the user callback routine, which passes the data collected from the UNIX device to the Explorer module. cxInputAdd returns a unique handle, which allows the module to distinguish more than one such input device.

When you use cxInputAdd, you should note that the callback routine is not called when the module is firing, only when it is quiescent.

The related subroutine, cxInputRemove, cancels the UNIX file descriptor monitoring process. You can call it from the callback routine specified in cxInputAdd.

cxInputAdd is a handy tool for monitoring, and collecting data from, processes outside the Explorer environment. For example, you can start up and communicate with a data base server from your Explorer module.

#include <stdio.h>
#include <cx/DataTypes.h>
#include <cx/ModuleCommand.h>

#ifdef __cplusplus
extern “C” {
#endif

void         selectTestFunc (
unsigned char *command )
{
    FILE           *fd;
    void           *handle;
    void            feedme();

    if (strlen(command) == 0) {
        return;
    }

    /*
     * First, send the user's command off for invocation, and hang on to a
     * descriptor for the pipe.
     */
    if ((fd = popen(command, “r”)) == NULL) {
        cxModAlert(“Command failed.”);
        return;
    }
    /*
     * Now, add this file descripter to the scheduler's select set. When
     * data arrives from the command, “feedme” will be called by Explorer. 
     */
    handle = cxInputAdd(fileno(fd), cx_InputReadMask,
                        feedme, (void *) fd);
    return;
}
/*
 * Input available callback.
 *
 * This is called when the file descriptor from the popen() call above is
 * available.  The client data (data) argument is just the FILE * form of the
 * descriptor.
 */

void        feedme( data, fd, handle )
void       *data;
int         fd;
void       *handle;
{
    char            buf[BUFSIZ];
    int             len;

    /*
      * Read from the pipe.  If no data remains on the file descriptor
      * (EOF) then remove the file descriptor from the select set.
     * Otherwise, just write the data to the window.
     */
    len = read(fd, buf, sizeof buf);

    if (len <= 0) {
        printf(“closing pipe\n”);
        pclose((FILE *) data);
        cxInputRemove(handle);
    } else {
        write(1, buf, len);
    }
}

#ifdef __cplusplus
};
#endif

You can use cxTimerAdd to time the occurrence of certain events. that relate to the module function. The module can request callback routines to be called after a delay of a specified number of milliseconds, or at specified intervals. For example, you can set the timer to operate once and then switch off, or to reset itself and continue to run.

The callback is made when the timer expires, but the user function must be quiescent at the time. If the timer expires while the user function is executing, the callback will not be made until it has completed execution, and the timing schedule will be thrown off.

You can use cxTimerRemove to cancel this routine.

Here is a sample module in C.

/*
 * Trigger module -- demonstrates cxTimerAdd()
 *
 * This module fires every X seconds, where X is the value on
 * the dial widget on its control panel
 */

#include <cx/DataTypes.h>
#include <cx/Timer.h>

#ifdef __cplusplus
extern “C” {
#endif

/*
 * Callback routine for the timer.
 * All this does is causes the module to fire.
 */

void myTrigger()
{
 cxFireASAP();
}

/*
 * Main user function.
 *
 * secs -- number of seconds to delay (from a dial)
 * newtime -- non-zero if the firing resulted from the dial changing
 */

void trigger ( long secs, long newtime )
{
 static void *lastTimer = NULL;

 /*
 * If the dial changed, remove any old interval timers and register a
 * new one. 
 */

 if (newtime) {
   if (lastTimer != NULL) {
    cxTimerRemove(lastTimer);
    }
    lastTimer = cxTimerAdd(secs * 1000, 1, myTrigger, 0);
 }
 printf(“triggered\n”);
}

#ifdef __cplusplus
};
#endif

You can use cxFilenameExpand to expand the name of a file fully to include the directory path. You can give it a string including, for example, ~ or $<environment variable>, and it will expand the variable into the full name. This is particularly useful because there is no standard C library routine for doing this.

The code for the following examples is in /usr/explorer/src/MWGcode/ Advanced/C/FilenameExpand.c.

#include <stdio.h>
#include <string.h>

#include <cx/DataAccess.h>

void expand(char *filename)
{
        /* terminate early if filename is empty */
        if ( strlen(filename) == 0 )
                return;

        /*
         The string returned by cxExpandFilename must be copied
         if it is to be saved for future use.  Subsequent calls
         to cxExpandFilename will write over this buffer.
        */
        printf(“delivered filename: %s\n”,filename);
        printf(“expanded filename:  %s\n”,cxExpandFilename(filename));

        /* increment counter for %n */
        cxFilenameIndexIncrement();
}

The plan is to create a directory where you have write permission (for example, beneath your home directory) and then develop modules in subdirectories of that directory. One or more modules may be developed in each subdirectory and you can build one or all of them with a single command.

First, reset the EXPLORERUSERHOME environment variable to the directory you have chosen as the Explorer installation directory; and place $EXPLORERHOME/bin in your execution path:

setenv EXPLORERUSERHOME /usr/local/explorer
set path = ($EXPLORERHOME/bin $path)

---

Note: Individual users do not always have write access to /usr/local/explorer on a multi-user system. In this case, set EXPLORERUSERHOME to a directory in which you do have write permission.

---

Decide where you want to do module development and create that directory. ~/explorer/modules is a good choice.

mkdir ~/explorer/modules

If ~/explorer does not already exist on your system, create it by typing:

mkdir ~/explorer

From here, you can proceed through one or the other, or both, of the following sections, depending on your purpose.

If you decide to build the sample Explorer modules provided in source format, you can compile them in your own source directory. To do this, first copy the sources into your directory:

cp -r /usr/explorer/src/* ~/explorer/modules

This assumes that explorer/modules is a directory in your home directory where you will build these modules. Next, make a Makefile in that directory:

cd ~/explorer/modules
cxmkmf 

Next, make sure that your EXPLORERUSERHOME environment variable is set to a place where you want these modules installed, for example:

setenv EXPLORERUSERHOME /usr/tmp/modules
mkdir $EXPLORERUSERHOME

Now, create Makefiles for those module subdirectories:

make Makefiles

Finally, you compile, link and install these modules:

make install

At the end, all of the sample modules should be compiled, linked, and installed.

If you decide to set up your own build system, you create subdirectories in which you can develop one or more modules. First copy the template Imakefile into your development directory and make it writable:

cp /usr/explorer/lib/Imakefile.modules Imakefile
chmod +w Imakefile

Then you can make a subdirectory (whose name may or may not match the module name you wish to use), and add that subdirectory to the list in Imakefile which starts with the line

MODULESUBDIRS = \

and is followed by a list of subdirectories containing modules. Any number of directory names can be listed, as long as they exist and are Explorer module development subdirectories.

You then build a new top-level Makefile, remake subdirectory Makefiles, and then proceed with development of the new module.

For example,

cd DIR
mkdir mycontour
vi Imakefile
 [add “mycontour to the MODULESUBDIRS list]
cxmkmf
make Makefiles
cd mycontour
make all

There are several environment variables that affect the way modules are built and installed. See “Configuring the Build Environment” in Chapter 2 for more information on these variables.

Each time you add a directory to the MODULESUBDIRS list, you must recreate the top-level Makefile with cxmkmf. Do not be tempted to edit the Makefile directly.

Once you have done this, the following commands will work in each module subdirectory:

The typical development cycle is to write your module user function, use the Module Builder to describe it, then use the Build option in the Module Builder to build it. Alternatively, you can describe the module first, then use the Module Builder to generate the function prototype. You can then fill in the code for the user function, and after that, build the module.

From this point on, you can rebuild the module at any time using the make all command. For more information, refer to Appendix A, “Using Makefiles.”

There are essentially three types of multiprocessing module, based upon: