TweetFollow Us on Twitter

Shared Libraries in CPX
Volume Number:12
Issue Number:8
Column Tag:Programming Workshop

Using Shared Libraries in CPX

Can you really use the Code Fragment Manager and not go crazy?

By John Shackelford

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

Introduction

The Power Mac and upgrades to System 7 harbor many exciting new technologies waiting for application developers to explore. One new technology allows executable code to be shared at run-time. This means you can share code libraries across applications regardless of which development environment you use - or in other words you can finally start using all that code those C++ developers are writing down the hall from you! This technology is provided by a new manager called the Code Fragment Manager (CFM). The CFM is responsible for loading fragments, blocks of executable PowerPC code and data, into memory, and preparing them for execution. Currently the CFM is supported only on Power Macs. However, very soon the CFM will be supported on 68K Macs.

This article describes and demonstrates with some example code one approach to accessing shared libraries from Prograph CPX. It shows a way to wrap a C/C++ library, defining an XPrim that provides the interface to shared libraries and describing in detail a set of CPX classes which encapsulate the use of shared libraries. You’ll receive many benefits from using shared libraries in your applications, including reduced development time (because non-Prograph code no longer has to be ported to the Prograph language) and increased application speed (because of the native Power Mac code). The code described in this article gives you the basic tools for accessing shared libraries, listing export symbols, connecting to shared libraries, and executing functions. The code is shareware, and can be found at Tangent Systems’ Web page.

Figure 1. The main window for the demo app

Shared Library Demo Application

For this article I have created a simple demo application and two shared libraries. The demo application will access the shared libraries. The libraries each contain a different implementation of the same set of functions. One library (OOSharedLib) implements a set of functions using C++ code, while the other library (ExampleCLib) uses all C code.

When the application launches and opens its main window (Figure 1), it also “opens” or “connects to” the two shared libraries. The exported symbols or functions contained in each library are then available for the application to use. The functions or symbols that a library exports are listed in the main window. The functions in each library have been designed to operate on an array of data, and can compute the maximum, minimum, average, variance, or sum of the data.

You can select the desired library by choosing its name in the pop-up menu. The scroll list on the left side of the window lists the exported symbols of the selected shared library. When a symbol is selected in this scrolling list, the Do Function button becomes active. When the Do Function button is pushed, the selected function in the selected library is executed. The results are then listed in the right-hand scroll list.

The pop-up menu in the window lists the two shared libraries the application will work with. These libraries are loaded when the main window opens by a call to the window’s method /loadLibraries (Figure 2). A «Shared Library» instance is created for each shared library and stored in an attribute of the main window for later use.

Figure 2. Test Window has a method which loads
a list of shared libraries

Exported symbols are the items which can be referenced by other code fragments. You can think of exported symbols as the public functions the library supports. Internally there may be a lot of functions that are hidden from the outside world. This provides some measure of control over how the library is used - which can be a nice feature for developers and users. As a developer, I may not always want every function in the library to be exposed, for fear they might not be properly used; and as a user, I may not want to know all the gory details of someone else’s library. The typical Power Mac development environment has a procedure you must follow to define the export symbols. In CodeWarrior, for instance, there is a file (*.exp) you can edit prior to building the shared library, that controls which symbols will be exported (more on this later on).

Now let’s try one function with the demo; then we will dive into more Prograph code. With the application still running, select a function in the function list and click Do Function (or simply double-click a function in the function list).

The demo application on the CPX side of things generates a list of 50 numbers. It then sends this list (embedded in a data structure) as an argument to the chosen function in the shared library. The shared library function then calculates the result and sends it back to the application (Figure 3). For the case where we use OOSharedLib and its get_average function, I did some timing analysis and found that a pure Prograph-coded equivalent using CPX built-in list primitives can be slower (I compared 68K compiled CPX to using a PPC-native shared library). Using 8000 values on a Power Mac 7100/80 (System 7.5), I got these results:

Interpreted CPX 200 Ticks

Compiled CPX 20 Ticks

Using native shared library < 1 Tick

(By the way, in looking at my Prograph code, don’t be put off by the idiosyncracies of my shorthand comments to myself, where I’m reminding myself what data type is being input or output. “<Shared Library>” means «Shared Library», an instance of the Shared Library class; at the time I was writing that comment I didn’t know how to type the '«' character! Use of parentheses generally indicates a list; so, for instance, “():name” means “a list of names”.)

Figure 3. The method /doFunction handles the execution of the selected library function

The local setup data_cache builds up a vector of data in a data structure to be sent off to the shared library. Figure 4 shows the fields of this structure. The functions in the shared library have been designed to return the result in the result field.

Figure 4. The data_cache fields
as shown in the CPX “info” window

SLD Kit CPX interface

On the CPX side of the things, the interface for using shared libraries is handled by a class called Shared Library. For Power Mac-native shared libraries you’ll actually use its subclass Shared Library PPC. When the port to 68K machines is complete, CPX users will use the Shared Library 68K subclass. The purpose of the Shared Library class is to encapsulate all the low-level calls to the CFM and the Mixed Mode Manager when working with shared libraries. The class provides a set of methods to access shared libraries. We will now review the six most significant of these methods.

Figure 5. /getLibrary gets a Connection ID to the shared library

/getLibrary

This method (Figure 5) retrieves a connection identification number using the toolbox call GetSharedLibrary. That call is in the local get shared library. The attribute Connection ID comes into play when using functions in the shared library or listing the exported symbols.

/closeLibrary

This method uses the Connection ID to close the connection (Figure 6).

Figure 6. /closeLibrary closes the connection to the shared library

/executeFunction

This method calls the function in the shared library (Figure 7). Two Shared Library methods are called prior to the final call to the shared library function via the XPrim exec-code-frag. The method /getGlue gets a chunk of embedded code (Shackelford [1994]) that exec-code-frag needs. The method /findSymbol gets a pointer to the function in the shared library. The XPrim exec-code-frag makes the call to the selected function.

Figure 7. /executeFunction encapsulates low-level CFM calls

Figure 8. /listSymbols obtains a list of function pointers

Figure 9. /listSymbolInfos gets basic information for symbols exported by a shared library

Figure 10. /findSymbol gets the function pointer
for a specific symbol by name

/listSymbols

This method can be used to get pointers to the functions exported by the shared library (Figure 8).

/listSymbolInfos

This method can be used to get pointers to the functions exported by the shared library, names of the functions, and SymClass for each function (Figure 9).

/findSymbol

This method can be used to get a specific function pointer. You must pass in the name of the function (Figure 10).

C++ Wrapper

For this article I created a small C++ library. I’ll show a function in that library and the wrapper code that was written to access it from CPX. The wrapper technique is basically the same for each function. I won’t discuss the pure C library (ExampleCLib), since the C++ version is more general as concerns the techniques required to access shared libraries from CPX. The C++ code is a simple class called Tvector. It provides a way to do calculations on a single-dimensional array of data. The next few listings show the declaration file for the shared library (OOSharedLib), the declaration file for the data structure we use to pass data into the shared libraries from CPX, the declaration file for the wrapper functions, the declaration file for the Tvector class, and the implementation files for the wrapper functions and the Tvector class.

Listing 1: OOSharedLib.h
Declaration file for the OOP shared library for this article.

#ifndef OOSHAREDLIB_H
#define OOSHAREDLIB_H
/*
    OOSharedLib.h
    
    Purpose: Header file for OOSharedLib.c
    
    This is the public function interface.
*/

#include "OOSharedLibStructs.h"

#if defined(__cplusplus)
extern "C" {
#endif


void get_average(data_cache *data);
void get_maximum(data_cache *data);
void get_minimum(data_cache *data);
void get_sum(data_cache *data);
void get_variance(data_cache *data);

#if defined(__cplusplus)
}
#endif
#endif

Listing 2: TanLibStructs.h

Declaration file for the data_cache. This is in a separate file so that we can use it with Prograph C Tool to 
“expose” or define the data structures for CPX - i.e. we can allocate the structure and fill the fields.

#ifndef TAN_LIB_STRUCTS_H
#define TAN_LIB_STRUCTS_H
/*
    © 1995 Tangent Systems
    All Rights Reserved.
    
    Public declarations for interface structures.
    Putting these declarations in a separate header makes it easier when it
    comes time to use Prograph C Tool to define these strcutures for use in CPX.
*/

#pragma pgtype double Real8
#pragma pgtype int Int4
#pragma pgtype unsigned Nat4

typedef struct {
 unsigned long length;
 int  success;
 double result;
 double *data;
 } data_cache;
 
#endif

Listing 3: Tvector.h

Declaration file for Tvector class. Defines simple methods for doing calculations on one dimensional arrays 
of doubles. Each Tvector has an array of doubles.

#ifndef TVECTOR_H
#define TVECTOR_H

class Tvector
{
 public:
    // Attributes
 unsigned long length;  // Number of element in this object
 double *theVector;
 
    // Methods
 Tvector(unsigned long length, double *aVector);
 ~Tvector();

 int calc_average(double *result);
 int calc_maximum(double *result);
 int calc_minimum(double *result);
 int calc_sum(double *result);
 int calc_variance(double *result);
 
 protected:
 
 private:
 int ok_vector;
 
};

#endif

As you can see, the class provides a constructor, a destructor, and five “mathematical” methods. Let’s look at get_average, which wraps the method calc_average. One limitation we have is that on the CPX side we will be allowed only one argument when making a call. So each wrapper will be designed to provide one argument - a pointer to a structure. We will handle the allocation and deletion of Tvector objects as needed.

Listing 4: get_average

Wraps method “calc_average” in class Tvector. Uses the Tvector class to calculate the average value of 
an array of doubles buried in data_cache.

/*
Pass in a pointer to data_cache, calculates the average value and returns
the answer in data_cache->result.
*/
void get_average(data_cache *theData)
{
 Tvector* aVector;
 double average = 0;
 TestDebug;
 
 aVector = new Tvector(theData->length, theData->data);
 theData->success = aVector->calc_average(&average);

 theData->result = average;
 delete(aVector);
}

The C function get_average instantiates a Tvector (aVector), passing the data to it (a pointer to data_cache). It then sends the message calc_average to aVector. The function captures the result in a local variable called average. The value of average is then passed back in the data_cache structure. All the wrappers are written so that there is only one calling argument and it is a pointer to a data structure. Here are the Tvector methods used in the wrapper function get_average.

Listing 5: Tvector

Constructor, destructor and method “calc_average” for class Tvector. This is only a partial listing of the 
the file Tvector.c.

Tvector::Tvector(unsigned long theLength, double *aVector)
{
 int i;
 ok_vector = 0;
 if(theLength < 0)
 {
 length = 0;
 return;
 }
 theVector = new double[theLength];

 for(i = 0;i < theLength; i++)
 {
 theVector[i] = aVector[i];
 }

 length = theLength;
 ok_vector = 1;
}
 
Tvector::~Tvector()
{
 delete(theVector);
 ok_vector = 0;
}

int Tvector::calc_average(double *result)
{
 int i;
 double theResult = 0;
 *result = theResult;
 if(ok_vector == 1)
 {
 for(i=0; i<length; i++)
 {
 theResult += theVector[i];
 }
 theResult = theResult/i;
 }
 *result = theResult;
 return ok_vector;
}

Building Shared Libraries

I used CodeWarrior for this article, and now I’ll show the files you’ll need to create a shared library. In general there are some special files you’ll need to include in the project file, there are some preferences you’ll have to set for the project, and then there is an export definition file (the .exp file) that you’ll need to define. According to the CodeWarrior documentation, you’ll need the files listed below under “libraries” and “MW Sources” (Figure 11).

Figure 11. To build a shared library
there are a few required files

Figure 12. Define the name of the shared library
in the PEF preference panel

Figure 13. Define the creator and type attributes of the shared library in the Project preference panel

Before building the shared library there a few preferences you’ll need to set up. See the CodeWarrior documentation for a complete description of the steps. I’ll highlight a few items to get you started. You’ll have to define the name of the library or fragment. That is defined in the “PEF” portion of the preferences in CodeWarrior (Figure 12).

You’ll also define the type and creator attributes, and the fact that the project is going to build a shared library. This is accomplished in the “Project” preferences panel (Figure 13).

One of the final steps before building the shared library is to define the symbols to be exported. If the Project file does not find the appropriate .exp file, it will export all functions. You can control what functions are made publicly available by creating a file with the same name as the project file, plus the .exp extension. When compilation occurs, the exported symbols will be those functions listed in the .exp file. So, for example, the project file for the OOSharedLib is called OOSharedLib.µ. The export file for this project would be named OOSharedLib.µ.exp. Listing 6 shows the content of the file in order to export our functions.

Listing 6: Export file

The export file defines the symbols that are made available for external use.

get_average
get_maximum
get_minimum
get_sum
get_variance

Conclusion and Future Plans

With the information in this article, CPX developers can now start planning, designing, and experimenting with shared libraries on the Power Mac. This powerful new feature of the Mac OS offers exciting possibilities to CPX developers, and the code in this article provides a mechanism to unleash that power.

We view the SLD Kit as another tool for CPX developers to use. We are developing a suite of high-performance technically-oriented shared libraries. The first commercial shared library we are releasing for CPX developers will be a Wavelet packet library. The core of the library is written in C++ and currently runs on DOS, Windows and UNIX. A CPX class will be developed to encapsulate the calls to the shared library. The class will provide basic data compression and Wavelet packet analysis functions. Potential application areas for such a library include voice compression, speech recognition, and digital communications.

Bibliography and References

Shackelford, John H. “You Can Have Your ‘C’ and Call It Too!”, Visual News 15 (November 1994) 9-12.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Latest Forum Discussions

See All

Six fantastic ways to spend National Vid...
As if anyone needed an excuse to play games today, I am about to give you one: it is National Video Games Day. A day for us to play games, like we no doubt do every day. Let’s not look a gift horse in the mouth. Instead, feast your eyes on this... | Read more »
Old School RuneScape players turn out in...
The sheer leap in technological advancements in our lifetime has been mind-blowing. We went from Commodore 64s to VR glasses in what feels like a heartbeat, but more importantly, the internet. It can be a dark mess, but it also brought hundreds of... | Read more »
Today's Best Mobile Game Discounts...
Every day, we pick out a curated list of the best mobile discounts on the App Store and post them here. This list won't be comprehensive, but it every game on it is recommended. Feel free to check out the coverage we did on them in the links below... | Read more »
Nintendo and The Pokémon Company's...
Unless you have been living under a rock, you know that Nintendo has been locked in an epic battle with Pocketpair, creator of the obvious Pokémon rip-off Palworld. Nintendo often resorts to legal retaliation at the drop of a hat, but it seems this... | Read more »
Apple exclusive mobile games don’t make...
If you are a gamer on phones, no doubt you have been as distressed as I am on one huge sticking point: exclusivity. For years, Xbox and PlayStation have done battle, and before this was the Sega Genesis and the Nintendo NES. On console, it makes... | Read more »
Regionally exclusive events make no sens...
Last week, over on our sister site AppSpy, I babbled excitedly about the Pokémon GO Safari Days event. You can get nine Eevees with an explorer hat per day. Or, can you? Specifically, you, reader. Do you have the time or funds to possibly fly for... | Read more »
As Jon Bellamy defends his choice to can...
Back in March, Jagex announced the appointment of a new CEO, Jon Bellamy. Mr Bellamy then decided to almost immediately paint a huge target on his back by cancelling the Runescapes Pride event. This led to widespread condemnation about his perceived... | Read more »
Marvel Contest of Champions adds two mor...
When I saw the latest two Marvel Contest of Champions characters, I scoffed. Mr Knight and Silver Samurai, thought I, they are running out of good choices. Then I realised no, I was being far too cynical. This is one of the things that games do best... | Read more »
Grass is green, and water is wet: Pokémo...
It must be a day that ends in Y, because Pokémon Trading Card Game Pocket has kicked off its Zoroark Drop Event. Here you can get a promo version of another card, and look forward to the next Wonder Pick Event and the next Mass Outbreak that will be... | Read more »
Enter the Gungeon review
It took me a minute to get around to reviewing this game for a couple of very good reasons. The first is that Enter the Gungeon's style of roguelike bullet-hell action is teetering on the edge of being straight-up malicious, which made getting... | Read more »

Price Scanner via MacPrices.net

Take $150 off every Apple 11-inch M3 iPad Air
Amazon is offering a $150 discount on 11-inch M3 WiFi iPad Airs right now. Shipping is free: – 11″ 128GB M3 WiFi iPad Air: $449, $150 off – 11″ 256GB M3 WiFi iPad Air: $549, $150 off – 11″ 512GB M3... Read more
Apple iPad minis back on sale for $100 off MS...
Amazon is offering $100 discounts (up to 20% off) on Apple’s newest 2024 WiFi iPad minis, each with free shipping. These are the lowest prices available for new minis among the Apple retailers we... Read more
Apple’s 16-inch M4 Max MacBook Pros are on sa...
Amazon has 16-inch M4 Max MacBook Pros (Silver and Black colors) on sale for up to $410 off Apple’s MSRP right now. Shipping is free. Be sure to select Amazon as the seller, rather than a third-party... Read more
Red Pocket Mobile is offering a $150 rebate o...
Red Pocket Mobile has new Apple iPhone 17’s on sale for $150 off MSRP when you switch and open up a new line of service. Red Pocket Mobile is a nationwide MVNO using all the major wireless carrier... Read more
Switch to Verizon, and get any iPhone 16 for...
With yesterday’s introduction of the new iPhone 17 models, Verizon responded by running “on us” promos across much of the iPhone 16 lineup: iPhone 16 and 16 Plus show as $0/mo for 36 months with bill... Read more
Here is a summary of the new features in Appl...
Apple’s September 2025 event introduced major updates across its most popular product lines, focusing on health, performance, and design breakthroughs. The AirPods Pro 3 now feature best-in-class... Read more
Apple’s Smartphone Lineup Could Use A Touch o...
COMMENTARY – Whatever happened to the old adage, “less is more”? Apple’s smartphone lineup. — which is due for its annual refresh either this month or next (possibly at an Apple Event on September 9... Read more
Take $50 off every 11th-generation A16 WiFi i...
Amazon has Apple’s 11th-generation A16 WiFi iPads in stock on sale for $50 off MSRP right now. Shipping is free: – 11″ 11th-generation 128GB WiFi iPads: $299 $50 off MSRP – 11″ 11th-generation 256GB... Read more
Sunday Sale: 14-inch M4 MacBook Pros for up t...
Don’t pay full price! Amazon has Apple’s 14-inch M4 MacBook Pros (Silver and Black colors) on sale for up to $220 off MSRP right now. Shipping is free. Be sure to select Amazon as the seller, rather... Read more
Mac mini with M4 Pro CPU back on sale for $12...
B&H Photo has Apple’s Mac mini with the M4 Pro CPU back on sale for $1259, $140 off MSRP. B&H offers free 1-2 day shipping to most US addresses: – Mac mini M4 Pro CPU (24GB/512GB): $1259, $... Read more

Jobs Board

All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.