When the user activates a project or tool icon, the program is run as a separate process asynchronous to Workbench. This allows the user to take full advantage of the multitasking features of the Amiga. A process is simply a task with additional information needed to use DOS library. When Workbench loads and starts a program, its sends the program a WBStartup message containing the arguments as described earlier. The WBStartup also contains a pointer to the new Process structure which describes the execution environment of the program. The WBStartup message is posted to the message port of the program's Process structure. The Process message port is for the exclusive use of DOS, so this message must be removed from the port before using any DOS library functions. Normally this is handled by the startup code module that comes with your compiler so you don't have to worry about this unless you are writing your own startup code. Standard startup code modules also set up SysBase, the pointer to the Exec master library, and open the DOS library setting up DOSBase. That is why Exec and AmigaDOS functions can be called by C applications without first opening a library; the startup code that applications are linked with handles this. Some special startups may also set up NIL: input and output streams, or may open a stdio window so that the Workbench applications can use stdio functions such as printf(). The startup code can tell if it is running in the Workbench environment because the pr_CLI field of the Process structure will contain NULL. In that case the startup code removes the WBStartup message from the Process message port with GetMsg() before using any functions in the DOS library. Do Not Use the Process Message Port for Anything Else. ------------------------------------------------------ The message port in a Process structure is for the exclusive use of the DOS library. Standard startup code will pass the WBStartup message pointer in argv and 0 (zero) in argc if the program is started from Workbench. These values are pushed onto the stack, and the startup code calls the application code that it is linked with as a function. When the application code exits back to the startup code, the startup code closes and frees all opens and allocations it made. It will then Forbid(), and ReplyMsg() the WBStartup message, notifying Workbench that the application Process may be terminated and its code unloaded from memory. Avoid the DOS Exit() function. ------------------------------ The DOS Exit() function does not return an application to the startup code that called it. If you wish to exit your application, use the exit function provided by your startup code (usually lower-case exit(), or _exit for assembler), passing it a valid DOS return code as listed in the include file <libraries/dos.h>.
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