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rfork ()
  • >> rfork (2) ( FreeBSD man: Системные вызовы )

  • BSD mandoc
     

    NAME

    
    
    rfork
    
     - manipulate process resources
    
     
    

    LIBRARY

    Lb libc
    
     
    

    SYNOPSIS

       #include <unistd.h>
    pid_t rfork (int flags);
     

    DESCRIPTION

    Forking, vforking or rforking are the only ways new processes are created. The Fa flags argument to rfork ();
    selects which resources of the invoking process (parent) are shared by the new process (child) or initialized to their default values. The resources include the open file descriptor table (which, when shared, permits processes to open and close files for other processes), and open files. The Fa flags argument is the logical OR of some subset of:

    RFPROC
    If set a new process is created; otherwise changes affect the current process.
    RFNOWAIT
    If set, the child process will be dissociated from the parent. Upon exit the child will not leave a status for the parent to collect. See wait(2).
    RFFDG
    If set, the invoker's file descriptor table (see intro(2)) is copied; otherwise the two processes share a single table.
    RFCFDG
    If set, the new process starts with a clean file descriptor table. Is mutually exclusive with RFFDG
    RFTHREAD
    If set, the new process shares file descriptor to process leaders table with its parent. Only applies when neither RFFDG nor RFCFDG are set.
    RFMEM
    If set, the kernel will force sharing of the entire address space, typically by sharing the hardware page table directly. The child will thus inherit and share all the segments the parent process owns, whether they are normally shareable or not. The stack segment is not split (both the parent and child return on the same stack) and thus rfork ();
    with the RFMEM flag may not generally be called directly from high level languages including C. May be set only with RFPROC A helper function is provided to assist with this problem and will cause the new process to run on the provided stack. See rfork_thread3 for information.
    RFSIGSHARE
    If set, the kernel will force sharing the sigacts structure between the child and the parent.
    RFLINUXTHPN
    If set, the kernel will return SIGUSR1 instead of SIGCHILD upon thread exit for the child. This is intended to mimic certain Linux clone behaviour.

    File descriptors in a shared file descriptor table are kept open until either they are explicitly closed or all processes sharing the table exit.

    If RFPROC is set, the value returned in the parent process is the process id of the child process; the value returned in the child is zero. Without RFPROC the return value is zero. Process id's range from 1 to the maximum integer ( int ) value. The rfork ();
    system call will sleep, if necessary, until required process resources are available.

    The fork ();
    system call can be implemented as a call to rfork (RFFDG | RFPROC);
    but is not for backwards compatibility.  

    RETURN VALUES

    Upon successful completion, rfork ();
    returns a value of 0 to the child process and returns the process ID of the child process to the parent process. Otherwise, a value of -1 is returned to the parent process, no child process is created, and the global variable errno is set to indicate the error.  

    ERRORS

    The rfork ();
    system call will fail and no child process will be created if:

    Bq Er EAGAIN
    The system-imposed limit on the total number of processes under execution would be exceeded. The limit is given by the sysctl(3) MIB variable KERN_MAXPROC (The limit is actually ten less than this except for the super user).
    Bq Er EAGAIN
    The user is not the super user, and the system-imposed limit on the total number of processes under execution by a single user would be exceeded. The limit is given by the sysctl(3) MIB variable KERN_MAXPROCPERUID
    Bq Er EAGAIN
    The user is not the super user, and the soft resource limit corresponding to the Fa resource argument RLIMIT_NOFILE would be exceeded (see getrlimit(2)).
    Bq Er EINVAL
    Both the RFFDG and the RFCFDG flags were specified.
    Bq Er EINVAL
    Any flags not listed above were specified.
    Bq Er ENOMEM
    There is insufficient swap space for the new process.

     

    SEE ALSO

    fork(2), intro(2), minherit(2), vfork(2), rfork_thread3  

    HISTORY

    The rfork ();
    function first appeared in Plan9.  

    BUGS

    Fx does not yet implement a native clone ();
    library call, and the current pthreads implementation does not use rfork ();
    with RFMEM. A native port of the linux threads library, /usr/ports/devel/linuxthreads contains a working clone ();
    call that utilizes RFMEM. The rfork_thread3 function can often be used instead of clone (.);


     

    Index

    NAME
    LIBRARY
    SYNOPSIS
    DESCRIPTION
    RETURN VALUES
    ERRORS
    SEE ALSO
    HISTORY
    BUGS


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