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LIBDLM(3)							     LIBDLM(3)

       libdlm	   -	  dlm_get_fd,	   dlm_dispatch,     dlm_pthread_init,
       dlm_ls_pthread_init, dlm_cleanup

       #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

       libdlm provides the programmatic userspace interface to the Distributed
       Lock  manager. It provides all the calls you need to manipulate locks &
       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 ini‐
       tialize 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	 call‐
       back  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

   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  pro‐
       vide 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

   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.

       There  also  exists a "light" version of the libdlm library called lib‐
       dlm_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

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

       ls = dlm_create_lockspace("myLS", 0660);


       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); = POLLIN;
	   while (!ast_called)
	       if (poll(&pfd, 1, 0) < 0)
		   return -1;
	   ast_called = 0;
	   return 0;

       libdlm(3),  dlm_lock(3), dlm_unlock(3), dlm_open_lockspace(3), dlm_cre‐
       ate_lockspace(3), dlm_close_lockspace(3), dlm_release_lockspace(3)

libdlm functions		 July 5, 2007			     LIBDLM(3)

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