LIBDLM(3)						     Library Functions Manual							 LIBDLM(3)

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  load-
       able 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)

libdlm functions						   July 5, 2007 							 LIBDLM(3)