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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. It is implemented in these steps: |
50 | Calling C<fork ()> is fully supported by this module - but you must not |
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51 | rely on this. It is currently implemented in these steps: |
51 | |
52 | |
52 | 1. wait till all requests in "execute" state have been handled |
53 | 1. wait till all requests in "execute" state have been handled |
53 | (basically requests that are already handed over to the kernel). |
54 | (basically requests that are already handed over to the kernel). |
54 | 2. fork |
55 | 2. fork |
55 | 3. in the parent, continue business as usual, done |
56 | 3. in the parent, continue business as usual, done |
56 | 4. in the child, destroy all ready and pending requests and free the |
57 | 4. in the child, destroy all ready and pending requests and free the |
57 | memory used by the worker threads. This gives you a fully empty |
58 | memory used by the worker threads. This gives you a fully empty |
58 | libeio queue. |
59 | libeio queue. |
59 | |
60 | |
60 | Note, however, since libeio does use threads, thr above guarantee doesn't |
61 | Note, however, since libeio does use threads, the above guarantee doesn't |
61 | cover your libc, for example, malloc and other libc functions are not |
62 | cover your libc, for example, malloc and other libc functions are not |
62 | fork-safe, so there is very little you can do after a fork, and in fatc, |
63 | fork-safe, so there is very little you can do after a fork, and in fact, |
63 | the above might crash, and thus change. |
64 | the above might crash, and thus change. |
64 | |
65 | |
65 | =head1 INITIALISATION/INTEGRATION |
66 | =head1 INITIALISATION/INTEGRATION |
66 | |
67 | |
67 | Before you can call any eio functions you first have to initialise the |
68 | Before you can call any eio functions you first have to initialise the |
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124 | =back |
125 | =back |
125 | |
126 | |
126 | For libev, you would typically use an C<ev_async> watcher: the |
127 | For libev, you would typically use an C<ev_async> watcher: the |
127 | C<want_poll> callback would invoke C<ev_async_send> to wake up the event |
128 | C<want_poll> callback would invoke C<ev_async_send> to wake up the event |
128 | loop. Inside the callback set for the watcher, one would call C<eio_poll |
129 | loop. Inside the callback set for the watcher, one would call C<eio_poll |
129 | ()> (followed by C<ev_async_send> again if C<eio_poll> indicates that not |
130 | ()>. |
130 | all requests have been handled yet). The race is taken care of because |
131 | |
131 | libev resets/rearms the async watcher before calling your callback, |
132 | If C<eio_poll ()> is configured to not handle all results in one go |
132 | and therefore, before calling C<eio_poll>. This might result in (some) |
133 | (i.e. it returns C<-1>) then you should start an idle watcher that calls |
133 | spurious wake-ups, but is generally harmless. |
134 | C<eio_poll> until it returns something C<!= -1>. |
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135 | |
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136 | A full-featured conenctor between libeio and libev would look as follows |
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137 | (if C<eio_poll> is handling all requests, it can of course be simplified a |
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138 | lot by removing the idle watcher logic): |
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139 | |
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140 | static struct ev_loop *loop; |
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141 | static ev_idle repeat_watcher; |
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142 | static ev_async ready_watcher; |
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143 | |
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144 | /* idle watcher callback, only used when eio_poll */ |
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145 | /* didn't handle all results in one call */ |
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146 | static void |
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147 | repeat (EV_P_ ev_idle *w, int revents) |
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148 | { |
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149 | if (eio_poll () != -1) |
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150 | ev_idle_stop (EV_A_ w); |
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151 | } |
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152 | |
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153 | /* eio has some results, process them */ |
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154 | static void |
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155 | ready (EV_P_ ev_async *w, int revents) |
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156 | { |
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157 | if (eio_poll () == -1) |
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158 | ev_idle_start (EV_A_ &repeat_watcher); |
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159 | } |
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160 | |
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161 | /* wake up the event loop */ |
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162 | static void |
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163 | want_poll (void) |
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164 | { |
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165 | ev_async_send (loop, &ready_watcher) |
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166 | } |
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167 | |
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168 | void |
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169 | my_init_eio () |
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170 | { |
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171 | loop = EV_DEFAULT; |
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172 | |
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173 | ev_idle_init (&repeat_watcher, repeat); |
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174 | ev_async_init (&ready_watcher, ready); |
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175 | ev_async_start (loop &watcher); |
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176 | |
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177 | eio_init (want_poll, 0); |
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178 | } |
134 | |
179 | |
135 | For most other event loops, you would typically use a pipe - the event |
180 | For most other event loops, you would typically use a pipe - the event |
136 | loop should be told to wait for read readiness on the read end. In |
181 | loop should be told to wait for read readiness on the read end. In |
137 | C<want_poll> you would write a single byte, in C<done_poll> you would try |
182 | C<want_poll> you would write a single byte, in C<done_poll> you would try |
138 | to read that byte, and in the callback for the read end, you would call |
183 | to read that byte, and in the callback for the read end, you would call |
139 | C<eio_poll>. The race is avoided here because the event loop should invoke |
184 | C<eio_poll>. |
140 | your callback again and again until the byte has been read (as the pipe |
185 | |
141 | read callback does not read it, only C<done_poll>). |
186 | You don't have to take special care in the case C<eio_poll> doesn't handle |
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187 | all requests, as the done callback will not be invoked, so the event loop |
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188 | will still signal readyness for the pipe until I<all> results have been |
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189 | processed. |
142 | |
190 | |
143 | |
191 | |
144 | =head1 HIGH LEVEL REQUEST API |
192 | =head1 HIGH LEVEL REQUEST API |
145 | |
193 | |
146 | Libeio has both a high-level API, which consists of calling a request |
194 | Libeio has both a high-level API, which consists of calling a request |
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218 | abort (); /* something ent wrong, we will all die!!! */ |
266 | abort (); /* something ent wrong, we will all die!!! */ |
219 | |
267 | |
220 | Note that you additionally need to call C<eio_poll> when the C<want_cb> |
268 | Note that you additionally need to call C<eio_poll> when the C<want_cb> |
221 | indicates that requests are ready to be processed. |
269 | indicates that requests are ready to be processed. |
222 | |
270 | |
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271 | =head2 CANCELLING REQUESTS |
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272 | |
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273 | Sometimes the need for a request goes away before the request is |
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274 | finished. In that case, one can cancel the reqiest by a call to |
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275 | C<eio_cancel>: |
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276 | |
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277 | =over 4 |
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278 | |
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279 | =item eio_cancel (eio_req *req) |
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280 | |
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281 | Cancel the request. If the request is currently executing it might still |
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282 | continue to execute, and in other cases it might still take a while till |
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283 | the request is cancelled. |
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284 | |
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285 | Even if cancelled, the finish callback will still be invoked - the |
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286 | callbacks of all cancellable requests need to check whether the request |
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287 | has been cancelled by calling C<EIO_CANCELLED (req)>: |
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288 | |
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289 | static int |
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290 | my_eio_cb (eio_req *req) |
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291 | { |
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292 | if (EIO_CANCELLED (req)) |
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293 | return 0; |
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294 | } |
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295 | |
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296 | In addition, cancelled requests will either have C<< req->result >> set to |
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297 | C<-1> and C<errno> to C<ECANCELED>, or otherwise they were successfully |
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298 | executed despite being cancelled (e.g. when they have already been |
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299 | executed at the time they were cancelled). |
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300 | |
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301 | =back |
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302 | |
223 | =head2 AVAILABLE REQUESTS |
303 | =head2 AVAILABLE REQUESTS |
224 | |
304 | |
225 | The following request functions are available. I<All> of them return the |
305 | The following request functions are available. I<All> of them return the |
226 | C<eio_req *> on success and C<0> on failure, and I<all> of them have the |
306 | C<eio_req *> on success and C<0> on failure, and I<all> of them have the |
227 | same three trailing arguments: C<pri>, C<cb> and C<data>. The C<cb> is |
307 | same three trailing arguments: C<pri>, C<cb> and C<data>. The C<cb> is |
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335 | =item eio_fstat (int fd, int pri, eio_cb cb, void *data) |
415 | =item eio_fstat (int fd, int pri, eio_cb cb, void *data) |
336 | |
416 | |
337 | Stats a file - if C<< req->result >> indicates success, then you can |
417 | Stats a file - if C<< req->result >> indicates success, then you can |
338 | access the C<struct stat>-like structure via C<< req->ptr2 >>: |
418 | access the C<struct stat>-like structure via C<< req->ptr2 >>: |
339 | |
419 | |
340 | EIO_STRUCT_STAT *statdata = (EIO_STRUCT_STAT *)req->ptr2; |
420 | EIO_STRUCT_STAT *statdata = (EIO_STRUCT_STAT *)req->ptr2; |
341 | |
421 | |
342 | =item eio_statvfs (const char *path, int pri, eio_cb cb, void *data) |
422 | =item eio_statvfs (const char *path, int pri, eio_cb cb, void *data) |
343 | |
423 | |
344 | =item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data) |
424 | =item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data) |
345 | |
425 | |
346 | Stats a filesystem - if C<< req->result >> indicates success, then you can |
426 | Stats a filesystem - if C<< req->result >> indicates success, then you can |
347 | access the C<struct statvfs>-like structure via C<< req->ptr2 >>: |
427 | access the C<struct statvfs>-like structure via C<< req->ptr2 >>: |
348 | |
428 | |
349 | EIO_STRUCT_STATVFS *statdata = (EIO_STRUCT_STATVFS *)req->ptr2; |
429 | EIO_STRUCT_STATVFS *statdata = (EIO_STRUCT_STATVFS *)req->ptr2; |
350 | |
430 | |
351 | =back |
431 | =back |
352 | |
432 | |
353 | =head3 READING DIRECTORIES |
433 | =head3 READING DIRECTORIES |
354 | |
434 | |
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394 | |
474 | |
395 | If this flag is specified, then, in addition to the names in C<ptr2>, |
475 | If this flag is specified, then, in addition to the names in C<ptr2>, |
396 | also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct |
476 | also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct |
397 | eio_dirent> looks like this: |
477 | eio_dirent> looks like this: |
398 | |
478 | |
399 | struct eio_dirent |
479 | struct eio_dirent |
400 | { |
480 | { |
401 | int nameofs; /* offset of null-terminated name string in (char *)req->ptr2 */ |
481 | int nameofs; /* offset of null-terminated name string in (char *)req->ptr2 */ |
402 | unsigned short namelen; /* size of filename without trailing 0 */ |
482 | unsigned short namelen; /* size of filename without trailing 0 */ |
403 | unsigned char type; /* one of EIO_DT_* */ |
483 | unsigned char type; /* one of EIO_DT_* */ |
404 | signed char score; /* internal use */ |
484 | signed char score; /* internal use */ |
405 | ino_t inode; /* the inode number, if available, otherwise unspecified */ |
485 | ino_t inode; /* the inode number, if available, otherwise unspecified */ |
406 | }; |
486 | }; |
407 | |
487 | |
408 | The only members you normally would access are C<nameofs>, which is the |
488 | The only members you normally would access are C<nameofs>, which is the |
409 | byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>. |
489 | byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>. |
410 | |
490 | |
411 | C<type> can be one of: |
491 | C<type> can be one of: |
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591 | Further below you will find more dicussion of these topics - first follows |
671 | Further below you will find more dicussion of these topics - first follows |
592 | the reference section detailing the request generator and other methods. |
672 | the reference section detailing the request generator and other methods. |
593 | |
673 | |
594 | =over 4 |
674 | =over 4 |
595 | |
675 | |
596 | =item eio_grp (eio_cb cb, void *data) |
676 | =item eio_req *grp = eio_grp (eio_cb cb, void *data) |
597 | |
677 | |
598 | Creates and submits a group request. |
678 | Creates, submits and returns a group request. |
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679 | |
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680 | =item eio_grp_add (eio_req *grp, eio_req *req) |
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681 | |
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682 | Adds a request to the request group. |
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683 | |
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684 | =item eio_grp_cancel (eio_req *grp) |
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685 | |
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686 | Cancels all requests I<in> the group, but I<not> the group request |
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687 | itself. You can cancel the group request via a normal C<eio_cancel> call. |
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688 | |
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689 | |
599 | |
690 | |
600 | =back |
691 | =back |
601 | |
692 | |
602 | |
693 | |
603 | |
694 | |
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607 | /* groups */ |
698 | /* groups */ |
608 | |
699 | |
609 | eio_req *eio_grp (eio_cb cb, void *data); |
700 | eio_req *eio_grp (eio_cb cb, void *data); |
610 | void eio_grp_feed (eio_req *grp, void (*feed)(eio_req *req), int limit); |
701 | void eio_grp_feed (eio_req *grp, void (*feed)(eio_req *req), int limit); |
611 | void eio_grp_limit (eio_req *grp, int limit); |
702 | void eio_grp_limit (eio_req *grp, int limit); |
612 | void eio_grp_add (eio_req *grp, eio_req *req); |
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613 | void eio_grp_cancel (eio_req *grp); /* cancels all sub requests but not the group */ |
703 | void eio_grp_cancel (eio_req *grp); /* cancels all sub requests but not the group */ |
614 | |
704 | |
615 | |
705 | |
616 | =back |
706 | =back |
617 | |
707 | |
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624 | =head1 ANATOMY AND LIFETIME OF AN EIO REQUEST |
714 | =head1 ANATOMY AND LIFETIME OF AN EIO REQUEST |
625 | |
715 | |
626 | A request is represented by a structure of type C<eio_req>. To initialise |
716 | A request is represented by a structure of type C<eio_req>. To initialise |
627 | it, clear it to all zero bytes: |
717 | it, clear it to all zero bytes: |
628 | |
718 | |
629 | eio_req req; |
719 | eio_req req; |
630 | |
720 | |
631 | memset (&req, 0, sizeof (req)); |
721 | memset (&req, 0, sizeof (req)); |
632 | |
722 | |
633 | A more common way to initialise a new C<eio_req> is to use C<calloc>: |
723 | A more common way to initialise a new C<eio_req> is to use C<calloc>: |
634 | |
724 | |
635 | eio_req *req = calloc (1, sizeof (*req)); |
725 | eio_req *req = calloc (1, sizeof (*req)); |
636 | |
726 | |
637 | In either case, libeio neither allocates, initialises or frees the |
727 | In either case, libeio neither allocates, initialises or frees the |
638 | C<eio_req> structure for you - it merely uses it. |
728 | C<eio_req> structure for you - it merely uses it. |
639 | |
729 | |
640 | zero |
730 | zero |