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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 |
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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 |
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57 | 4. in the child, destroy all ready and pending requests and free the |
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58 | memory used by the worker threads. This gives you a fully empty |
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59 | libeio queue. |
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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 |
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63 | typically works. |
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64 | |
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65 | Otherwise, the only recommendation you should follow is: treat fork code |
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66 | the same way you treat signal handlers, and only ever call C<eio_init> in |
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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 |
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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. |
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86 | |
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87 | There is currently no way to change these callbacks later, or to |
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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", |
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707 | =head4 GROUP REQUEST LIFETIME |
713 | =head4 GROUP REQUEST LIFETIME |
708 | |
714 | |
709 | Left alone, a group request will instantly move to the pending state and |
715 | Left alone, a group request will instantly move to the pending state and |
710 | will be finished at the next call of C<eio_poll>. |
716 | will be finished at the next call of C<eio_poll>. |
711 | |
717 | |
712 | There usefulness stems from the fact that, if a subrequest is added to a |
718 | The usefulness stems from the fact that, if a subrequest is added to a |
713 | group I<before> a call to C<eio_poll>, via C<eio_grp_add>, then the group |
719 | group I<before> a call to C<eio_poll>, via C<eio_grp_add>, then the group |
714 | will not finish until all the subrequests have finished. |
720 | will not finish until all the subrequests have finished. |
715 | |
721 | |
716 | So the usage cycle of a group request is like this: after it is created, |
722 | So the usage cycle of a group request is like this: after it is created, |
717 | you normally instantly add a subrequest. If none is added, the group |
723 | you normally instantly add a subrequest. If none is added, the group |
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738 | can return as "the load request". |
744 | can return as "the load request". |
739 | |
745 | |
740 | =item 2) open the file, maybe |
746 | =item 2) open the file, maybe |
741 | |
747 | |
742 | Next, open the file with C<eio_open> and add the request to the group |
748 | Next, open the file with C<eio_open> and add the request to the group |
743 | request and you are finished steting up the request. |
749 | request and you are finished setting up the request. |
744 | |
750 | |
745 | If, for some reason, you cannot C<eio_open> (path is a null ptr?) you |
751 | If, for some reason, you cannot C<eio_open> (path is a null ptr?) you |
746 | cna set C<< grp->result >> to C<-1> to signal an error and let the gorup |
752 | can set C<< grp->result >> to C<-1> to signal an error and let the group |
747 | request finish on its own. |
753 | request finish on its own. |
748 | |
754 | |
749 | =item 3) open callback adds more requests |
755 | =item 3) open callback adds more requests |
750 | |
756 | |
751 | In the open callback, if the open was not successful, copy C<< |
757 | In the open callback, if the open was not successful, copy C<< |
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753 | C<-1> to signal an error. |
759 | C<-1> to signal an error. |
754 | |
760 | |
755 | Otherwise, malloc some memory or so and issue a read request, adding the |
761 | Otherwise, malloc some memory or so and issue a read request, adding the |
756 | read request to the group. |
762 | read request to the group. |
757 | |
763 | |
758 | =item 4) continue issuign requests till finished |
764 | =item 4) continue issuing requests till finished |
759 | |
765 | |
760 | In the real callback, check for errors and possibly continue with |
766 | In the real callback, check for errors and possibly continue with |
761 | C<eio_close> or any other eio request in the same way. |
767 | C<eio_close> or any other eio request in the same way. |
762 | |
768 | |
763 | As soon as no new requests are added the group request will finish. Make |
769 | As soon as no new requests are added the group request will finish. Make |
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909 | This symbol governs the stack size for each eio thread. Libeio itself |
915 | This symbol governs the stack size for each eio thread. Libeio itself |
910 | was written to use very little stackspace, but when using C<EIO_CUSTOM> |
916 | was written to use very little stackspace, but when using C<EIO_CUSTOM> |
911 | requests, you might want to increase this. |
917 | requests, you might want to increase this. |
912 | |
918 | |
913 | If this symbol is undefined (the default) then libeio will use its default |
919 | If this symbol is undefined (the default) then libeio will use its default |
914 | stack size (C<sizeof (long) * 4096> currently). If it is defined, but |
920 | stack size (C<sizeof (void *) * 4096> currently). If it is defined, but |
915 | C<0>, then the default operating system stack size will be used. In all |
921 | C<0>, then the default operating system stack size will be used. In all |
916 | other cases, the value must be an expression that evaluates to the desired |
922 | other cases, the value must be an expression that evaluates to the desired |
917 | stack size. |
923 | stack size. |
918 | |
924 | |
919 | =back |
925 | =back |