2. Process Creation and Execution Manager¶

2.1. Introduction¶

The process creation and execution manager provides the functionality associated with the creation and termination of processes.

The directives provided by the process creation and execution manager are:

• fork - Create a Process
• execl - Execute a File
• execv - Execute a File
• execle - Execute a File
• execve - Execute a File
• execlp - Execute a File
• execvp - Execute a File
• pthread_atfork - Register Fork Handlers
• wait - Wait for Process Termination
• waitpid - Wait for Process Termination
• _exit - Terminate a Process

2.2. Background¶

POSIX process functionality can not be completely supported by RTEMS. This is because RTEMS provides no memory protection and implements a single process, multi-threaded execution model. In this light, RTEMS provides none of the routines that are associated with the creation of new processes. However, since the entire RTEMS application (e.g. executable) is logically a single POSIX process, RTEMS is able to provide implementations of many operations on processes. The rule of thumb is that those routines provide a meaningful result. For example, getpid() returns the node number.

2.3. Operations¶

The only functionality method defined by this manager which is supported by RTEMS is the _exit service. The implementation of _exit shuts the application down and is equivalent to invoking either exit or rtems_shutdown_executive.

2.4. Directives¶

This section details the process creation and execution manager’s directives. A subsection is dedicated to each of this manager’s directives and describes the calling sequence, related constants, usage, and status codes.

#include <sys/types.h>
int fork( void );

int execl(
    const char *path,
    const char *arg,
    ...
);

int execv(
    const char *path,
    char const *argv[],
    ...
);

int execle(
    const char *path,
    const char *arg,
    ...
);

int execve(
    const char *path,
    char *const argv[],
    char *const envp[]
);

int execlp(
    const char *file,
    const char *arg,
    ...
);

int execvp(
    const char *file,
    char *const argv[],
    ...
);

#include <sys/types.h>
int pthread_atfork(
    void (*prepare)(void),
    void (*parent)(void),
    void (*child)(void)
);

#include <sys/types.h>
#include <sys/wait.h>
int wait(
    int *stat_loc
);

int wait(
    pid_t  pid,
    int   *stat_loc,
    int    options
);

void _exit(
    int status
);