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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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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 | |
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238 | Members not explicitly described as accessible must not be |
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239 | accessed. Specifically, there is no guarantee that any members will still |
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240 | have the value they had when the request was submitted. |
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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: |
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586 | =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) |
587 | |
597 | |
588 | 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 |
589 | emulated by simply reading the data (currently in 64kiB chunks). |
599 | emulated by simply reading the data (currently in 64kiB chunks). |
590 | |
600 | |
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|
601 | =item eio_syncfs (int fd, int pri, eio_cb cb, void *data) |
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602 | |
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|
603 | Calls Linux' C<syncfs> syscall, if available. Returns C<-1> and sets |
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|
604 | C<errno> to C<ENOSYS> if the call is missing I<but still calls sync()>, |
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605 | if the C<fd> is C<< >= 0 >>, so you can probe for the availability of the |
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606 | syscall with a negative C<fd> argument and checking for C<-1/ENOSYS>. |
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|
607 | |
591 | =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) |
592 | |
609 | |
593 | 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 |
594 | as calling C<fdatasync>. |
611 | as calling C<fdatasync>. |
595 | |
612 | |
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… | |
613 | |
630 | |
614 | =over 4 |
631 | =over 4 |
615 | |
632 | |
616 | =item eio_mtouch (void *addr, size_t length, int flags, int pri, eio_cb cb, void *data) |
633 | =item eio_mtouch (void *addr, size_t length, int flags, int pri, eio_cb cb, void *data) |
617 | |
634 | |
618 | Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY) the given |
635 | Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY>) the given |
619 | memory area, page-wise, that is, it reads (or reads and writes back) the |
636 | memory area, page-wise, that is, it reads (or reads and writes back) the |
620 | first octet of every page that spans the memory area. |
637 | first octet of every page that spans the memory area. |
621 | |
638 | |
622 | This can be used to page in some mmapped file, or dirty some pages. Note |
639 | This can be used to page in some mmapped file, or dirty some pages. Note |
623 | that dirtying is an unlocked read-write access, so races can ensue when |
640 | that dirtying is an unlocked read-write access, so races can ensue when |
… | |
… | |
747 | request finish on its own. |
764 | request finish on its own. |
748 | |
765 | |
749 | =item 3) open callback adds more requests |
766 | =item 3) open callback adds more requests |
750 | |
767 | |
751 | In the open callback, if the open was not successful, copy C<< |
768 | In the open callback, if the open was not successful, copy C<< |
752 | req->errorno >> to C<< grp->errorno >> and set C<< grp->errorno >> to |
769 | req->errorno >> to C<< grp->errorno >> and set C<< grp->result >> to |
753 | C<-1> to signal an error. |
770 | C<-1> to signal an error. |
754 | |
771 | |
755 | Otherwise, malloc some memory or so and issue a read request, adding the |
772 | Otherwise, malloc some memory or so and issue a read request, adding the |
756 | read request to the group. |
773 | read request to the group. |
757 | |
774 | |
758 | =item 4) continue issuing requests till finished |
775 | =item 4) continue issuing requests till finished |
759 | |
776 | |
760 | In the real callback, check for errors and possibly continue with |
777 | In the read callback, check for errors and possibly continue with |
761 | C<eio_close> or any other eio request in the same way. |
778 | C<eio_close> or any other eio request in the same way. |
762 | |
779 | |
763 | As soon as no new requests are added the group request will finish. Make |
780 | As soon as no new requests are added, the group request will finish. Make |
764 | sure you I<always> set C<< grp->result >> to some sensible value. |
781 | sure you I<always> set C<< grp->result >> to some sensible value. |
765 | |
782 | |
766 | =back |
783 | =back |
767 | |
784 | |
768 | =head4 REQUEST LIMITING |
785 | =head4 REQUEST LIMITING |
… | |
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909 | 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 |
910 | 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> |
911 | requests, you might want to increase this. |
928 | requests, you might want to increase this. |
912 | |
929 | |
913 | 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 |
914 | 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 |
915 | 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 |
916 | 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 |
917 | stack size. |
934 | stack size. |
918 | |
935 | |
919 | =back |
936 | =back |