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Full Discussion: Ideas: 'select'ing file descriptors
Top Forums Programming Ideas: 'select'ing file descriptors Post 48114 by DreamWarrior on Thursday 26th of February 2004 03:47:54 PM
Old 02-26-2004
Quote:
Originally posted by Perderabo
I didn't really follow all of that, but I would try to go in one of two directions...

1) Lose that memory queue
--snip--

2) Lose that pipe
--snip--
1) Well, the memory queue is a requirement because the pipe has a byte limit and given the threaded nature and the need for mutex protection it is possible that I run up against a deadlock because the read thread is trying to lock a structure to handle a request and the write thread has it locked but can put it on the pipe because of the byte limit.

I found that out the hard way...and that's why the single byte on and off to prevent this.

2) That's so close to polling it might as well be polling and would decrease the overall responsiveness of the system because I'd have to wait for socket events, switch to wait for response events, and then back. This also wastes CPU cycles as most polling type activity does...and that's bad practice IMO.

As for the race condition...there really is not worry there. First the mutex will protect the memory queue. So a thread putting a request on it has a consistent view of whether it is the first to put a request on or not. The thread taking the data off then (after it locks the mutex) has a consistent view of whether that item is the "last" item. If another is to be added the mutex has to be aquired, which it can not be until the read thread either removes the byte and the request (or the write thread places the byte and the "first" request).

What I'm really looking for is a way to, maybe with fcntl, make a file (rather than a pipe...maybe one open to /dev/null) readable and then non-readable so that a select can see the readable flag set, and then I can clear it. This is acheived with the single byte outstanding on the pipe...but I'm looking for a cleaner way.

Thanks for the suggestions, if you have any more ideas I'd love to hear them.
 

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LEARN ABOUT DEBIAN

gearman_worker_timeout

GEARMAN_WORKER_TIMEOUT(3)					     Gearmand						 GEARMAN_WORKER_TIMEOUT(3)

NAME

       gearman_worker_timeout - Gearmand Documentation, http://gearman.info/

SYNOPSIS

       #include <libgearman/gearman.h>

       gearman_worker_st

       gearman_worker_set_task_context_free_fn

       int gearman_worker_timeout(gearman_worker_st *worker)

       void gearman_worker_set_timeout(gearman_worker_st *worker, int timeout)

       void *gearman_worker_context(const gearman_worker_st *worker)

       void gearman_worker_set_context(gearman_worker_st *worker, void *context)

       void gearman_worker_set_workload_malloc_fn(gearman_worker_st *worker, gearman_malloc_fn *function, void *context)

       void gearman_worker_set_workload_free_fn(gearman_worker_st *worker, gearman_free_fn *function, void *context)

       gearman_return_t gearman_worker_wait(gearman_worker_st *worker)

       gearman_return_t gearman_worker_register(gearman_worker_st *worker, const char *function_name, uint32_t timeout)

       gearman_return_t gearman_worker_unregister(gearman_worker_st *worker, const char *function_name)

       gearman_return_t gearman_worker_unregister_all(gearman_worker_st *worker)

       gearman_job_st *gearman_worker_grab_job(gearman_worker_st *worker, gearman_job_st *job, gearman_return_t *ret_ptr)

       void gearman_job_free_all(gearman_worker_st *worker)

       bool gearman_worker_function_exist(gearman_worker_st *worker, const char *function_name, size_t function_length)

       gearman_return_t gearman_worker_work(gearman_worker_st *worker)

       Link with -lgearman

DESCRIPTION

       gearman_worker_st is used for worker communication with the server.

       gearman_worker_context() and gearman_worker_set_context() can be used to store an arbitrary object for the user.

       gearman_worker_set_task_context_free_fn() sets a trigger that will be called when a gearman_task_st is released.

       gearman_worker_timeout() and gearman_worker_set_timeout() get and set the current timeout value, in milliseconds, for the worker.

       gearman_worker_function_exist() is used to determine if a given worker has a specific function.

       Normally   malloc(3)   and   free(3)   are  used  for  allocation  and  releasing  workloads.  gearman_worker_set_workload_malloc_fn()  and
       gearman_worker_set_workload_free_fn() can be used to replace these with custom functions.

       If you need to remove a function from the server you can call either gearman_worker_unregister_all()  to  remove  all  functions  that  the
       worker has told the gearmand server about, or you can use gearman_worker_unregister() to remove just a single function.

RETURN

       Various

HOME

       To find out more information please check: http://gearman.info/

SEE ALSO

       gearmand(8) libgearman(3)

AUTHOR

       Data Differential http://www.datadifferential.com/

COPYRIGHT

       2012, Data Differential, http://www.datadifferential.com/

0.33								   May 04, 2012 					 GEARMAN_WORKER_TIMEOUT(3)
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