… | |
… | |
45 | Unlike the name component C<stamp> might indicate, it is also used for |
45 | Unlike the name component C<stamp> might indicate, it is also used for |
46 | time differences throughout libeio. |
46 | time differences throughout libeio. |
47 | |
47 | |
48 | =head2 FORK SUPPORT |
48 | =head2 FORK SUPPORT |
49 | |
49 | |
50 | Calling C<fork ()> is fully supported by this module - but you must not |
50 | Usage of pthreads in a program changes the semantics of fork |
51 | rely on this. It is currently implemented in these steps: |
51 | considerably. Specifically, only async-safe functions can be called after |
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|
52 | fork. Libeio uses pthreads, so this applies, and makes using fork hard for |
|
|
53 | anything but relatively fork + exec uses. |
52 | |
54 | |
53 | 1. wait till all requests in "execute" state have been handled |
55 | This library only works in the process that initialised it: Forking is |
54 | (basically requests that are already handed over to the kernel). |
56 | fully supported, but using libeio in any other process than the one that |
55 | 2. fork |
57 | called 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 | |
61 | Note, however, since libeio does use threads, the above guarantee doesn't |
59 | You might get around by not I<using> libeio before (or after) forking in |
62 | cover your libc, for example, malloc and other libc functions are not |
60 | the parent, and using it in the child afterwards. You could also try to |
63 | fork-safe, so there is very little you can do after a fork, and in fact, |
61 | call the L<eio_init> function again in the child, which will brutally |
64 | the above might crash, and thus change. |
62 | reinitialise all data structures, which isn't POSIX conformant, but |
|
|
63 | typically works. |
|
|
64 | |
|
|
65 | Otherwise, the only recommendation you should follow is: treat fork code |
|
|
66 | the same way you treat signal handlers, and only ever call C<eio_init> in |
|
|
67 | the process that uses it, and only once ever. |
65 | |
68 | |
66 | =head1 INITIALISATION/INTEGRATION |
69 | =head1 INITIALISATION/INTEGRATION |
67 | |
70 | |
68 | Before you can call any eio functions you first have to initialise the |
71 | Before you can call any eio functions you first have to initialise the |
69 | library. The library integrates into any event loop, but can also be used |
72 | library. The library integrates into any event loop, but can also be used |
… | |
… | |
78 | This function initialises the library. On success it returns C<0>, on |
81 | This function initialises the library. On success it returns C<0>, on |
79 | failure it returns C<-1> and sets C<errno> appropriately. |
82 | failure it returns C<-1> and sets C<errno> appropriately. |
80 | |
83 | |
81 | It accepts two function pointers specifying callbacks as argument, both of |
84 | It accepts two function pointers specifying callbacks as argument, both of |
82 | which can be C<0>, in which case the callback isn't called. |
85 | which can be C<0>, in which case the callback isn't called. |
|
|
86 | |
|
|
87 | There 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 | |
86 | The C<want_poll> callback is invoked whenever libeio wants attention (i.e. |
92 | The C<want_poll> callback is invoked whenever libeio wants attention (i.e. |
87 | it wants to be polled by calling C<eio_poll>). It is "edge-triggered", |
93 | it wants to be polled by calling C<eio_poll>). It is "edge-triggered", |
… | |
… | |
131 | |
137 | |
132 | If C<eio_poll ()> is configured to not handle all results in one go |
138 | If C<eio_poll ()> is configured to not handle all results in one go |
133 | (i.e. it returns C<-1>) then you should start an idle watcher that calls |
139 | (i.e. it returns C<-1>) then you should start an idle watcher that calls |
134 | C<eio_poll> until it returns something C<!= -1>. |
140 | C<eio_poll> until it returns something C<!= -1>. |
135 | |
141 | |
136 | A full-featured conenctor between libeio and libev would look as follows |
142 | A full-featured connector between libeio and libev would look as follows |
137 | (if C<eio_poll> is handling all requests, it can of course be simplified a |
143 | (if C<eio_poll> is handling all requests, it can of course be simplified a |
138 | lot by removing the idle watcher logic): |
144 | lot by removing the idle watcher logic): |
139 | |
145 | |
140 | static struct ev_loop *loop; |
146 | static struct ev_loop *loop; |
141 | static ev_idle repeat_watcher; |
147 | static ev_idle repeat_watcher; |
… | |
… | |
227 | |
233 | |
228 | The C<void *data> member simply stores the value of the C<data> argument. |
234 | The C<void *data> member simply stores the value of the C<data> argument. |
229 | |
235 | |
230 | =back |
236 | =back |
231 | |
237 | |
|
|
238 | Members not explicitly described as accessible must not be |
|
|
239 | accessed. Specifically, there is no guarantee that any members will still |
|
|
240 | have the value they had when the request was submitted. |
|
|
241 | |
232 | The return value of the callback is normally C<0>, which tells libeio to |
242 | The return value of the callback is normally C<0>, which tells libeio to |
233 | continue normally. If a callback returns a nonzero value, libeio will |
243 | continue normally. If a callback returns a nonzero value, libeio will |
234 | stop processing results (in C<eio_poll>) and will return the value to its |
244 | stop processing results (in C<eio_poll>) and will return the value to its |
235 | caller. |
245 | caller. |
236 | |
246 | |
237 | Memory areas passed to libeio must stay valid as long as a request |
247 | Memory areas passed to libeio wrappers must stay valid as long as a |
238 | executes, with the exception of paths, which are being copied |
248 | request executes, with the exception of paths, which are being copied |
239 | internally. Any memory libeio itself allocates will be freed after the |
249 | internally. Any memory libeio itself allocates will be freed after the |
240 | finish callback has been called. If you want to manage all memory passed |
250 | finish callback has been called. If you want to manage all memory passed |
241 | to libeio yourself you can use the low-level API. |
251 | to libeio yourself you can use the low-level API. |
242 | |
252 | |
243 | For example, to open a file, you could do this: |
253 | For example, to open a file, you could do this: |
… | |
… | |
405 | free (target); |
415 | free (target); |
406 | } |
416 | } |
407 | |
417 | |
408 | =item eio_realpath (const char *path, int pri, eio_cb cb, void *data) |
418 | =item eio_realpath (const char *path, int pri, eio_cb cb, void *data) |
409 | |
419 | |
410 | Similar to the realpath libc function, but unlike that one, result is |
420 | Similar to the realpath libc function, but unlike that one, C<< |
411 | C<-1> on failure and the length of the returned path in C<ptr2> (which is |
421 | req->result >> is C<-1> on failure. On success, the result is the length |
412 | not 0-terminated) - this is similar to readlink. |
422 | of the returned path in C<ptr2> (which is I<NOT> 0-terminated) - this is |
|
|
423 | similar to readlink. |
413 | |
424 | |
414 | =item eio_stat (const char *path, int pri, eio_cb cb, void *data) |
425 | =item eio_stat (const char *path, int pri, eio_cb cb, void *data) |
415 | |
426 | |
416 | =item eio_lstat (const char *path, int pri, eio_cb cb, void *data) |
427 | =item eio_lstat (const char *path, int pri, eio_cb cb, void *data) |
417 | |
428 | |
… | |
… | |
585 | =item eio_readahead (int fd, off_t offset, size_t length, int pri, eio_cb cb, void *data) |
596 | =item eio_readahead (int fd, off_t offset, size_t length, int pri, eio_cb cb, void *data) |
586 | |
597 | |
587 | Calls C<readahead(2)>. If the syscall is missing, then the call is |
598 | Calls C<readahead(2)>. If the syscall is missing, then the call is |
588 | emulated by simply reading the data (currently in 64kiB chunks). |
599 | emulated by simply reading the data (currently in 64kiB chunks). |
589 | |
600 | |
|
|
601 | =item eio_syncfs (int fd, int pri, eio_cb cb, void *data) |
|
|
602 | |
|
|
603 | Calls Linux' C<syncfs> syscall, if available. Returns C<-1> and sets |
|
|
604 | C<errno> to C<ENOSYS> if the call is missing I<but still calls sync()>, |
|
|
605 | if the C<fd> is C<< >= 0 >>, so you can probe for the availability of the |
|
|
606 | syscall with a negative C<fd> argument and checking for C<-1/ENOSYS>. |
|
|
607 | |
590 | =item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data) |
608 | =item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data) |
591 | |
609 | |
592 | Calls C<sync_file_range>. If the syscall is missing, then this is the same |
610 | Calls C<sync_file_range>. If the syscall is missing, then this is the same |
593 | as calling C<fdatasync>. |
611 | as calling C<fdatasync>. |
594 | |
612 | |
595 | Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>, |
613 | Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>, |
596 | C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>. |
614 | C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>. |
|
|
615 | |
|
|
616 | =item eio_fallocate (int fd, int mode, off_t offset, off_t len, int pri, eio_cb cb, void *data) |
|
|
617 | |
|
|
618 | Calls C<fallocate> (note: I<NOT> C<posix_fallocate>!). If the syscall is |
|
|
619 | missing, then it returns failure and sets C<errno> to C<ENOSYS>. |
|
|
620 | |
|
|
621 | The C<mode> argument can be C<0> (for behaviour similar to |
|
|
622 | C<posix_fallocate>), or C<EIO_FALLOC_FL_KEEP_SIZE>, which keeps the size |
|
|
623 | of the file unchanged (but still preallocates space beyond end of file). |
597 | |
624 | |
598 | =back |
625 | =back |
599 | |
626 | |
600 | =head3 LIBEIO-SPECIFIC REQUESTS |
627 | =head3 LIBEIO-SPECIFIC REQUESTS |
601 | |
628 | |
… | |
… | |
677 | |
704 | |
678 | =over 4 |
705 | =over 4 |
679 | |
706 | |
680 | =item eio_req *grp = eio_grp (eio_cb cb, void *data) |
707 | =item eio_req *grp = eio_grp (eio_cb cb, void *data) |
681 | |
708 | |
682 | Creates, submits and returns a group request. |
709 | Creates, submits and returns a group request. Note that it doesn't have a |
|
|
710 | priority, unlike all other requests. |
683 | |
711 | |
684 | =item eio_grp_add (eio_req *grp, eio_req *req) |
712 | =item eio_grp_add (eio_req *grp, eio_req *req) |
685 | |
713 | |
686 | Adds a request to the request group. |
714 | Adds a request to the request group. |
687 | |
715 | |
688 | =item eio_grp_cancel (eio_req *grp) |
716 | =item eio_grp_cancel (eio_req *grp) |
689 | |
717 | |
690 | Cancels all requests I<in> the group, but I<not> the group request |
718 | Cancels all requests I<in> the group, but I<not> the group request |
691 | itself. You can cancel the group request via a normal C<eio_cancel> call. |
719 | itself. You can cancel the group request I<and> all subrequests via a |
|
|
720 | normal C<eio_cancel> call. |
692 | |
721 | |
693 | |
|
|
694 | |
|
|
695 | =back |
722 | =back |
696 | |
723 | |
|
|
724 | =head4 GROUP REQUEST LIFETIME |
|
|
725 | |
|
|
726 | Left alone, a group request will instantly move to the pending state and |
|
|
727 | will be finished at the next call of C<eio_poll>. |
|
|
728 | |
|
|
729 | The usefulness stems from the fact that, if a subrequest is added to a |
|
|
730 | group I<before> a call to C<eio_poll>, via C<eio_grp_add>, then the group |
|
|
731 | will not finish until all the subrequests have finished. |
|
|
732 | |
|
|
733 | So the usage cycle of a group request is like this: after it is created, |
|
|
734 | you normally instantly add a subrequest. If none is added, the group |
|
|
735 | request will finish on it's own. As long as subrequests are added before |
|
|
736 | the group request is finished it will be kept from finishing, that is the |
|
|
737 | callbacks of any subrequests can, in turn, add more requests to the group, |
|
|
738 | and as long as any requests are active, the group request itself will not |
|
|
739 | finish. |
|
|
740 | |
|
|
741 | =head4 CREATING COMPOSITE REQUESTS |
|
|
742 | |
|
|
743 | Imagine you wanted to create an C<eio_load> request that opens a file, |
|
|
744 | reads it and closes it. This means it has to execute at least three eio |
|
|
745 | requests, but for various reasons it might be nice if that request looked |
|
|
746 | like any other eio request. |
|
|
747 | |
|
|
748 | This can be done with groups: |
|
|
749 | |
|
|
750 | =over 4 |
|
|
751 | |
|
|
752 | =item 1) create the request object |
|
|
753 | |
|
|
754 | Create a group that contains all further requests. This is the request you |
|
|
755 | can return as "the load request". |
|
|
756 | |
|
|
757 | =item 2) open the file, maybe |
|
|
758 | |
|
|
759 | Next, open the file with C<eio_open> and add the request to the group |
|
|
760 | request and you are finished setting up the request. |
|
|
761 | |
|
|
762 | If, for some reason, you cannot C<eio_open> (path is a null ptr?) you |
|
|
763 | can set C<< grp->result >> to C<-1> to signal an error and let the group |
|
|
764 | request finish on its own. |
|
|
765 | |
|
|
766 | =item 3) open callback adds more requests |
|
|
767 | |
|
|
768 | In the open callback, if the open was not successful, copy C<< |
|
|
769 | req->errorno >> to C<< grp->errorno >> and set C<< grp->result >> to |
|
|
770 | C<-1> to signal an error. |
|
|
771 | |
|
|
772 | Otherwise, malloc some memory or so and issue a read request, adding the |
|
|
773 | read request to the group. |
|
|
774 | |
|
|
775 | =item 4) continue issuing requests till finished |
|
|
776 | |
|
|
777 | In the read callback, check for errors and possibly continue with |
|
|
778 | C<eio_close> or any other eio request in the same way. |
|
|
779 | |
|
|
780 | As soon as no new requests are added, the group request will finish. Make |
|
|
781 | sure you I<always> set C<< grp->result >> to some sensible value. |
|
|
782 | |
|
|
783 | =back |
|
|
784 | |
|
|
785 | =head4 REQUEST LIMITING |
697 | |
786 | |
698 | |
787 | |
699 | #TODO |
788 | #TODO |
700 | |
789 | |
701 | /*****************************************************************************/ |
|
|
702 | /* groups */ |
|
|
703 | |
|
|
704 | eio_req *eio_grp (eio_cb cb, void *data); |
|
|
705 | void eio_grp_feed (eio_req *grp, void (*feed)(eio_req *req), int limit); |
|
|
706 | void eio_grp_limit (eio_req *grp, int limit); |
790 | void eio_grp_limit (eio_req *grp, int limit); |
707 | void eio_grp_cancel (eio_req *grp); /* cancels all sub requests but not the group */ |
|
|
708 | |
791 | |
709 | |
792 | |
710 | =back |
793 | =back |
711 | |
794 | |
712 | |
795 | |
… | |
… | |
843 | This symbol governs the stack size for each eio thread. Libeio itself |
926 | This symbol governs the stack size for each eio thread. Libeio itself |
844 | was written to use very little stackspace, but when using C<EIO_CUSTOM> |
927 | was written to use very little stackspace, but when using C<EIO_CUSTOM> |
845 | requests, you might want to increase this. |
928 | requests, you might want to increase this. |
846 | |
929 | |
847 | If this symbol is undefined (the default) then libeio will use its default |
930 | If this symbol is undefined (the default) then libeio will use its default |
848 | stack size (C<sizeof (long) * 4096> currently). If it is defined, but |
931 | stack size (C<sizeof (void *) * 4096> currently). If it is defined, but |
849 | C<0>, then the default operating system stack size will be used. In all |
932 | C<0>, then the default operating system stack size will be used. In all |
850 | other cases, the value must be an expression that evaluates to the desired |
933 | other cases, the value must be an expression that evaluates to the desired |
851 | stack size. |
934 | stack size. |
852 | |
935 | |
853 | =back |
936 | =back |