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MPE/iX Developer's Kit Reference Manual Volume I: HP 3000 MPE/iX Computer Systems > Chapter 3
MPE/iX Library Implementation Considerations
Process Management |
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This section provides an overview of implementation considerations that you must understand when creating and managing processes as they are implemented in the POSIX/iX library. For more information about how processes are created and managed in a POSIX.1 environment, refer to chapter 6, "Process Creation and Synchronization", in The POSIX.1 Standard - A Programmer's Guide (36430-90003). The implementation and behavior of processes created through the POSIX/iX library conform in most respects to the POSIX.1 standard. In most cases, underlying MPE/iX process features are transparent to a POSIX.1 application; however, there are some MPE/iX features outside the scope of the POSIX.1 standard that cannot be hidden from your application. These additional implementation features must be taken into account when you are creating and managing processes through the POSIX/iX library.
The following implementation considerations must be understood when using fork() or an exec() function to create or execute processes.
An executable file that is compiled and linked using the c89 command (available through the MPE/iX Shell) always creates an executable file with an MPE/iX file code of NMPRG. Attempts to use an exec() function to execute a file that has a file code of anything other than NMPRG results in an error, with errno set to ENOEXEC. To determine whether a file has an MPE/iX file code of NMPRG, you must use the MPE/iX CI command LISTFILE. For more information about using the LISTFILE command, refer to MPE/iX Commands Reference manual. By default, MPE/iX restricts an application's ability to spawn multiple processes. The MPE/iX process handling (PH) capability allows the creation of multiple processes. There are two levels of restrictions that apply if an application wishes to invoke the fork() function or exec() functions:
Because processes created through POSIX/iX library functions reside in an MPE/iX process environment, certain MPE/iX process attributes are inherited by a process created by fork(); however, these MPE/iX process attributes are not visible in the POSIX/iX environment. For example, the following MPE/iX process attributes are inherited by a new process created by fork():
Also, some MPE/iX process attributes that are not defined by the POSIX.1 standard are not inherited by the child process. The lack of these attributes does not affect the behavior of a process created in the POSIX/iX environment. On MPE/iX, if a parent process terminates without waiting for all of its child processes to terminate, the resulting "orphaned" child processes are terminated immediately prior to termination of the parent process. The implementation does not allow orphaned child processes to be adopted by a system process. Your application should not rely upon orphaned child processes being adopted by a system process. No user process can be a controlling process. Only system processes, such as the MPE/iX Command Interpreter (CI), are allowed to be controlling processes. The controlling terminal is not disassociated from the session when a user process terminates. The controlling terminal is associated with the MPE/iX CI session that invokes the application. The controlling terminal is only disassociated when the MPE/iX session is ended (when the user logs off the system using the BYE command). CPU time accounting information accrued by process is not made available to the parent process through the wait() and waitpid() functions. A zero is always returned. Attempts to use the fork() or exec() function to create a new process fails if the calling process
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