NAME

       libdlm - dlm_get_fd, dlm_dispatch, dlm_pthread_init, dlm_ls_pthread_init, dlm_cleanup

SYNOPSIS

       #include <libdlm.h>
       int dlm_pthread_init();
       int dlm_ls_pthread_init(dlm_lshandle_t lockspace);
       int dlm_pthread_cleanup();
       int dlm_get_fd(void);
       int dlm_dispatch(int fd);

       link with -ldlm

DESCRIPTION

       libdlm  provides  the programmatic userspace interface to the Distributed Lock manager. It
       provides all the calls you need to manipulate locks & lockspaces
       libdlm can be used in pthread or non-pthread applications. For pthread applications simply
       call  the  following  function before doing any lock operations. If you're using pthreads,
       remember to define _REENTRANT at the top of the  program  or  using  -D_REENTRANT  on  the
       compile line.
       pthreads  is  the  normal  way  of using the DLM. This way you simply initialize the DLM's
       thread and all the AST routines will be delivered  in  that  thread.  You  just  call  the
       dlm_lock() etc routines in the main line of your program.
       If  you  don't  want  to use pthreads or you want to handle the dlm callback ASTs yourself
       then you can get an FD handle to the DLM device and call dlm_dispatch() on it whenever  it
       becomes  active. That was ASTs will be delivered in the context of the thread/process that
       called dlm_dispatch().

   int dlm_pthread_init()
       Creates a thread to receive all lock ASTs. The AST callback function for  lock  operations
       will  be  called in the context of this thread. If there is a potential for local resource
       access conflicts you must provide your own pthread-based locking in the AST routine.

   int dlm_ls_pthread_init(dlm_lshandle_t lockspace)
       As dlm_pthread_init but initializes a thread for the specified lockspace.

   int dlm_pthread_cleanup()
       Cleans up the default lockspace threads after use. Normally you don't need to  call  this,
       but  if the locking code is in a dynamically loadable shared library this will probably be
       necessary.
       For non-pthread based applications the DLM provides a file descriptor that the program can
       feed  into poll/select. If activity is detected on that FD then a dispatch function should
       be called:

   int dlm_get_fd()
       Returns a file-descriptor for the DLM suitable for passing in to poll() or select().

   int dlm_dispatch(int fd)
       Reads from the DLM and calls any AST routines that may be needed. This routine runs in the
       context of the caller so no extra locking is needed to protect local resources.

libdlm_lt

       There  also  exists  a  "light"  version  of  the libdlm library called libdlm_lt. This is
       provided for those applications that do not want to use pthread functions. If you use this
       library  it is important that your application is NOT compiled with -D_REENTRANT or linked
       with libpthread.

EXAMPLES

       Create a lockspace and start a thread to deliver its callbacks:
       dlm_lshandle_t ls;

       ls = dlm_create_lockspace("myLS", 0660);
       dlm_ls_pthread_init(ls);

        ...

       status = dlm_ls_lock(ls,
                            ... );

        Using poll(2) to wait for and dispatch ASTs

       static int poll_for_ast(dlm_lshandle_t ls)
       {
           struct pollfd pfd;

           pfd.fd = dlm_ls_get_fd(ls);
           pfd.events = POLLIN;
           while (!ast_called)
           {
               if (poll(&pfd, 1, 0) < 0)
               {
                   perror("poll");
                   return -1;
               }
               dlm_dispatch(dlm_ls_get_fd(ls));
           }
           ast_called = 0;
           return 0;
       }

SEE ALSO

       libdlm(3),  dlm_lock(3),  dlm_unlock(3),  dlm_open_lockspace(3),  dlm_create_lockspace(3),
       dlm_close_lockspace(3), dlm_release_lockspace(3)