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Revision 1.20 by sf-exg, Thu Jul 7 17:35:52 2011 UTC vs.
Revision 1.26 by root, Mon Jul 18 02:59:58 2011 UTC

… …
45Unlike the name component C<stamp> might indicate, it is also used for 45Unlike the name component C<stamp> might indicate, it is also used for
46time differences throughout libeio. 46time differences throughout libeio.
47 47
48=head2 FORK SUPPORT 48=head2 FORK SUPPORT
49 49
50Calling C<fork ()> is fully supported by this module - but you must not 50Usage of pthreads in a program changes the semantics of fork
51rely on this. It is currently implemented in these steps: 51considerably. Specifically, only async-safe functions can be called after
52fork. Libeio uses pthreads, so this applies, and makes using fork hard for
53anything but relatively fork + exec uses.
52 54
53 1. wait till all requests in "execute" state have been handled 55This library only works in the process that initialised it: Forking is
54 (basically requests that are already handed over to the kernel). 56fully supported, but using libeio in any other process than the one that
55 2. fork 57called C<eio_init> is not.
56 3. in the parent, continue business as usual, done
57 4. in the child, destroy all ready and pending requests and free the
58 memory used by the worker threads. This gives you a fully empty
59 libeio queue.
60 58
61Note, however, since libeio does use threads, the above guarantee doesn't 59You might get around by not I<using> libeio before (or after) forking in
62cover your libc, for example, malloc and other libc functions are not 60the parent, and using it in the child afterwards. You could also try to
63fork-safe, so there is very little you can do after a fork, and in fact, 61call the L<eio_init> function again in the child, which will brutally
64the above might crash, and thus change. 62reinitialise all data structures, which isn't POSIX conformant, but
63typically works.
64
65Otherwise, the only recommendation you should follow is: treat fork code
66the same way you treat signal handlers, and only ever call C<eio_init> in
67the process that uses it, and only once ever.
65 68
66=head1 INITIALISATION/INTEGRATION 69=head1 INITIALISATION/INTEGRATION
67 70
68Before you can call any eio functions you first have to initialise the 71Before you can call any eio functions you first have to initialise the
69library. The library integrates into any event loop, but can also be used 72library. The library integrates into any event loop, but can also be used
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78This function initialises the library. On success it returns C<0>, on 81This function initialises the library. On success it returns C<0>, on
79failure it returns C<-1> and sets C<errno> appropriately. 82failure it returns C<-1> and sets C<errno> appropriately.
80 83
81It accepts two function pointers specifying callbacks as argument, both of 84It accepts two function pointers specifying callbacks as argument, both of
82which can be C<0>, in which case the callback isn't called. 85which can be C<0>, in which case the callback isn't called.
86
87There is currently no way to change these callbacks later, or to
88"uninitialise" the library again.
83 89
84=item want_poll callback 90=item want_poll callback
85 91
86The C<want_poll> callback is invoked whenever libeio wants attention (i.e. 92The C<want_poll> callback is invoked whenever libeio wants attention (i.e.
87it wants to be polled by calling C<eio_poll>). It is "edge-triggered", 93it wants to be polled by calling C<eio_poll>). It is "edge-triggered",
… …
405 free (target); 411 free (target);
406 } 412 }
407 413
408=item eio_realpath (const char *path, int pri, eio_cb cb, void *data) 414=item eio_realpath (const char *path, int pri, eio_cb cb, void *data)
409 415
410Similar to the realpath libc function, but unlike that one, result is 416Similar to the realpath libc function, but unlike that one, C<<
411C<-1> on failure and the length of the returned path in C<ptr2> (which is 417req->result >> is C<-1> on failure. On success, the result is the length
412not 0-terminated) - this is similar to readlink. 418of the returned path in C<ptr2> (which is I<NOT> 0-terminated) - this is
419similar to readlink.
413 420
414=item eio_stat (const char *path, int pri, eio_cb cb, void *data) 421=item eio_stat (const char *path, int pri, eio_cb cb, void *data)
415 422
416=item eio_lstat (const char *path, int pri, eio_cb cb, void *data) 423=item eio_lstat (const char *path, int pri, eio_cb cb, void *data)
417 424
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593as calling C<fdatasync>. 600as calling C<fdatasync>.
594 601
595Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>, 602Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,
596C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>. 603C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
597 604
605=item eio_fallocate (int fd, int mode, off_t offset, off_t len, int pri, eio_cb cb, void *data)
606
607Calls C<fallocate> (note: I<NOT> C<posix_fallocate>!). If the syscall is
608missing, then it returns failure and sets C<errno> to C<ENOSYS>.
609
610The C<mode> argument can be C<0> (for behaviour similar to
611C<posix_fallocate>), or C<EIO_FALLOC_FL_KEEP_SIZE>, which keeps the size
612of the file unchanged (but still preallocates space beyond end of file).
613
598=back 614=back
599 615
600=head3 LIBEIO-SPECIFIC REQUESTS 616=head3 LIBEIO-SPECIFIC REQUESTS
601 617
602These requests are specific to libeio and do not correspond to any OS call. 618These requests are specific to libeio and do not correspond to any OS call.
… …
677 693
678=over 4 694=over 4
679 695
680=item eio_req *grp = eio_grp (eio_cb cb, void *data) 696=item eio_req *grp = eio_grp (eio_cb cb, void *data)
681 697
682Creates, submits and returns a group request. 698Creates, submits and returns a group request. Note that it doesn't have a
699priority, unlike all other requests.
683 700
684=item eio_grp_add (eio_req *grp, eio_req *req) 701=item eio_grp_add (eio_req *grp, eio_req *req)
685 702
686Adds a request to the request group. 703Adds a request to the request group.
687 704
688=item eio_grp_cancel (eio_req *grp) 705=item eio_grp_cancel (eio_req *grp)
689 706
690Cancels all requests I<in> the group, but I<not> the group request 707Cancels all requests I<in> the group, but I<not> the group request
691itself. You can cancel the group request via a normal C<eio_cancel> call. 708itself. You can cancel the group request I<and> all subrequests via a
709normal C<eio_cancel> call.
692 710
693
694
695=back 711=back
696 712
713=head4 GROUP REQUEST LIFETIME
714
715Left alone, a group request will instantly move to the pending state and
716will be finished at the next call of C<eio_poll>.
717
718The usefulness stems from the fact that, if a subrequest is added to a
719group I<before> a call to C<eio_poll>, via C<eio_grp_add>, then the group
720will not finish until all the subrequests have finished.
721
722So the usage cycle of a group request is like this: after it is created,
723you normally instantly add a subrequest. If none is added, the group
724request will finish on it's own. As long as subrequests are added before
725the group request is finished it will be kept from finishing, that is the
726callbacks of any subrequests can, in turn, add more requests to the group,
727and as long as any requests are active, the group request itself will not
728finish.
729
730=head4 CREATING COMPOSITE REQUESTS
731
732Imagine you wanted to create an C<eio_load> request that opens a file,
733reads it and closes it. This means it has to execute at least three eio
734requests, but for various reasons it might be nice if that request looked
735like any other eio request.
736
737This can be done with groups:
738
739=over 4
740
741=item 1) create the request object
742
743Create a group that contains all further requests. This is the request you
744can return as "the load request".
745
746=item 2) open the file, maybe
747
748Next, open the file with C<eio_open> and add the request to the group
749request and you are finished setting up the request.
750
751If, for some reason, you cannot C<eio_open> (path is a null ptr?) you
752can set C<< grp->result >> to C<-1> to signal an error and let the group
753request finish on its own.
754
755=item 3) open callback adds more requests
756
757In the open callback, if the open was not successful, copy C<<
758req->errorno >> to C<< grp->errorno >> and set C<< grp->errorno >> to
759C<-1> to signal an error.
760
761Otherwise, malloc some memory or so and issue a read request, adding the
762read request to the group.
763
764=item 4) continue issuing requests till finished
765
766In the real callback, check for errors and possibly continue with
767C<eio_close> or any other eio request in the same way.
768
769As soon as no new requests are added the group request will finish. Make
770sure you I<always> set C<< grp->result >> to some sensible value.
771
772=back
773
774=head4 REQUEST LIMITING
697 775
698 776
699#TODO 777#TODO
700 778
701/*****************************************************************************/
702/* groups */
703
704eio_req *eio_grp (eio_cb cb, void *data);
705void eio_grp_feed (eio_req *grp, void (*feed)(eio_req *req), int limit);
706void eio_grp_limit (eio_req *grp, int limit); 779void eio_grp_limit (eio_req *grp, int limit);
707void eio_grp_cancel (eio_req *grp); /* cancels all sub requests but not the group */
708 780
709 781
710=back 782=back
711 783
712 784
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843This symbol governs the stack size for each eio thread. Libeio itself 915This symbol governs the stack size for each eio thread. Libeio itself
844was written to use very little stackspace, but when using C<EIO_CUSTOM> 916was written to use very little stackspace, but when using C<EIO_CUSTOM>
845requests, you might want to increase this. 917requests, you might want to increase this.
846 918
847If this symbol is undefined (the default) then libeio will use its default 919If this symbol is undefined (the default) then libeio will use its default
848stack size (C<sizeof (long) * 4096> currently). If it is defined, but 920stack size (C<sizeof (void *) * 4096> currently). If it is defined, but
849C<0>, then the default operating system stack size will be used. In all 921C<0>, then the default operating system stack size will be used. In all
850other cases, the value must be an expression that evaluates to the desired 922other cases, the value must be an expression that evaluates to the desired
851stack size. 923stack size.
852 924
853=back 925=back

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