vfork()

create new process that shares the same address as calling process 

Function


SYNOPSIS

#include <unistd.h>

pid_t vfork(void);


DESCRIPTION

The vfork() function creates a new process as does fork(), except that the child process shares the same address space as the calling process. Execution of the calling process is blocked until the child process calls one of the exec() family of functions, or calls _exit(). Because parent and child share the address space, you must not return from the function that called vfork(); doing so can corrupt the parent's stack.

You should use vfork() when your child process simply modifies the process state and then calls one of the exec() functions. Because of the shared address space, you must avoid doing anything in the child that impacts the parent when it resumes execution. For example, if your exec() call fails, you must call _exit(), and not exit(), because calling exit() would close standard I/O stream buffers for the parent as well as the child.

Handlers registered with pthread_atfork() are not invoked when vfork() is called, because doing so would adversely affect the shared address space.


PARAMETERS

None.


RETURN VALUES

If successful, vfork() returns 0 in the child process, and returns the process ID of the child process to the parent process. On failure, it returns -1 and sets errno to one of the following values:

EAGAIN 

The system lacked the necessary resources to create another process, or the system-imposed limit on the total number of processes under execution system-wide would be exceeded.


CONFORMANCE

UNIX 98, with exceptions.


MULTITHREAD SAFETY LEVEL

Unsafe.


PORTING ISSUES

The vfork() function provides an efficient mechanism to create a new process, in those instances where you need to manipulate process state (for example, closing file descriptors) prior calling one of the exec() family of functions. vfork() does not create a new Windows process context, however. Hence calling getpid() in the child of a vfork() operation returns the same value as in the parent. The process ID returned by vfork() is actually the process ID of the exec()ed child. Refer to Process Management in the Windows Concepts chapter of the PTC MKS Toolkit UNIX to Windows Porting Guide for a detailed discussion of the process model.


AVAILABILITY

PTC MKS Toolkit for Professional Developers
PTC MKS Toolkit for Enterprise Developers
PTC MKS Toolkit for Enterprise Developers 64-Bit Edition


SEE ALSO

Functions:
_exit(), execl(), execle(), execlp(), execlpe(), execv(), execve(), execvp(), execvpe(), exit(), fork(), getpid(), pthread_atfork()


PTC MKS Toolkit 9.6 Documentation Build 9.