… | |
… | |
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 | Usage of pthreads in a program changes the semantics of fork |
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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. |
51 | |
54 | |
52 | 1. wait till all requests in "execute" state have been handled |
55 | This library only works in the process that initialised it: Forking is |
53 | (basically requests that are already handed over to the kernel). |
56 | fully supported, but using libeio in any other process than the one that |
54 | 2. fork |
57 | called C<eio_init> is not. |
55 | 3. in the parent, continue business as usual, done |
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56 | 4. in the child, destroy all ready and pending requests and free the |
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57 | memory used by the worker threads. This gives you a fully empty |
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58 | libeio queue. |
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59 | |
58 | |
60 | Note, however, since libeio does use threads, thr above guarantee doesn't |
59 | You might get around by not I<using> libeio before (or after) forking in |
61 | 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 |
62 | fork-safe, so there is very little you can do after a fork, and in fatc, |
61 | call the L<eio_init> function again in the child, which will brutally |
63 | 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. |
64 | |
68 | |
65 | =head1 INITIALISATION/INTEGRATION |
69 | =head1 INITIALISATION/INTEGRATION |
66 | |
70 | |
67 | 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 |
68 | 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 |
… | |
… | |
77 | 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 |
78 | failure it returns C<-1> and sets C<errno> appropriately. |
82 | failure it returns C<-1> and sets C<errno> appropriately. |
79 | |
83 | |
80 | It accepts two function pointers specifying callbacks as argument, both of |
84 | It accepts two function pointers specifying callbacks as argument, both of |
81 | 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. |
82 | |
89 | |
83 | =item want_poll callback |
90 | =item want_poll callback |
84 | |
91 | |
85 | 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. |
86 | 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", |
… | |
… | |
124 | =back |
131 | =back |
125 | |
132 | |
126 | For libev, you would typically use an C<ev_async> watcher: the |
133 | 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 |
134 | 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 |
135 | 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 |
136 | ()>. |
130 | all requests have been handled yet). The race is taken care of because |
137 | |
131 | libev resets/rearms the async watcher before calling your callback, |
138 | 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) |
139 | (i.e. it returns C<-1>) then you should start an idle watcher that calls |
133 | spurious wake-ups, but is generally harmless. |
140 | C<eio_poll> until it returns something C<!= -1>. |
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141 | |
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142 | A full-featured connector between libeio and libev would look as follows |
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143 | (if C<eio_poll> is handling all requests, it can of course be simplified a |
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144 | lot by removing the idle watcher logic): |
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145 | |
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146 | static struct ev_loop *loop; |
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147 | static ev_idle repeat_watcher; |
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148 | static ev_async ready_watcher; |
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149 | |
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150 | /* idle watcher callback, only used when eio_poll */ |
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151 | /* didn't handle all results in one call */ |
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152 | static void |
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153 | repeat (EV_P_ ev_idle *w, int revents) |
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154 | { |
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155 | if (eio_poll () != -1) |
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156 | ev_idle_stop (EV_A_ w); |
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157 | } |
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158 | |
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159 | /* eio has some results, process them */ |
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160 | static void |
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161 | ready (EV_P_ ev_async *w, int revents) |
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162 | { |
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163 | if (eio_poll () == -1) |
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164 | ev_idle_start (EV_A_ &repeat_watcher); |
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165 | } |
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166 | |
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167 | /* wake up the event loop */ |
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168 | static void |
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169 | want_poll (void) |
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170 | { |
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171 | ev_async_send (loop, &ready_watcher) |
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172 | } |
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173 | |
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174 | void |
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175 | my_init_eio () |
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176 | { |
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177 | loop = EV_DEFAULT; |
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178 | |
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179 | ev_idle_init (&repeat_watcher, repeat); |
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180 | ev_async_init (&ready_watcher, ready); |
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181 | ev_async_start (loop &watcher); |
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182 | |
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183 | eio_init (want_poll, 0); |
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184 | } |
134 | |
185 | |
135 | For most other event loops, you would typically use a pipe - the event |
186 | 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 |
187 | 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 |
188 | 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 |
189 | 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 |
190 | C<eio_poll>. |
140 | your callback again and again until the byte has been read (as the pipe |
191 | |
141 | read callback does not read it, only C<done_poll>). |
192 | You don't have to take special care in the case C<eio_poll> doesn't handle |
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193 | all requests, as the done callback will not be invoked, so the event loop |
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194 | will still signal readiness for the pipe until I<all> results have been |
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195 | processed. |
142 | |
196 | |
143 | |
197 | |
144 | =head1 HIGH LEVEL REQUEST API |
198 | =head1 HIGH LEVEL REQUEST API |
145 | |
199 | |
146 | Libeio has both a high-level API, which consists of calling a request |
200 | Libeio has both a high-level API, which consists of calling a request |
… | |
… | |
179 | |
233 | |
180 | 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. |
181 | |
235 | |
182 | =back |
236 | =back |
183 | |
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 | |
184 | 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 |
185 | continue normally. If a callback returns a nonzero value, libeio will |
243 | continue normally. If a callback returns a nonzero value, libeio will |
186 | 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 |
187 | caller. |
245 | caller. |
188 | |
246 | |
189 | 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 |
190 | executes, with the exception of paths, which are being copied |
248 | request executes, with the exception of paths, which are being copied |
191 | internally. Any memory libeio itself allocates will be freed after the |
249 | internally. Any memory libeio itself allocates will be freed after the |
192 | 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 |
193 | to libeio yourself you can use the low-level API. |
251 | to libeio yourself you can use the low-level API. |
194 | |
252 | |
195 | For example, to open a file, you could do this: |
253 | For example, to open a file, you could do this: |
… | |
… | |
213 | } |
271 | } |
214 | |
272 | |
215 | /* the first three arguments are passed to open(2) */ |
273 | /* the first three arguments are passed to open(2) */ |
216 | /* the remaining are priority, callback and data */ |
274 | /* the remaining are priority, callback and data */ |
217 | if (!eio_open ("/etc/passwd", O_RDONLY, 0, 0, file_open_done, 0)) |
275 | if (!eio_open ("/etc/passwd", O_RDONLY, 0, 0, file_open_done, 0)) |
218 | abort (); /* something ent wrong, we will all die!!! */ |
276 | abort (); /* something went wrong, we will all die!!! */ |
219 | |
277 | |
220 | Note that you additionally need to call C<eio_poll> when the C<want_cb> |
278 | Note that you additionally need to call C<eio_poll> when the C<want_cb> |
221 | indicates that requests are ready to be processed. |
279 | indicates that requests are ready to be processed. |
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280 | |
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281 | =head2 CANCELLING REQUESTS |
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282 | |
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283 | Sometimes the need for a request goes away before the request is |
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284 | finished. In that case, one can cancel the request by a call to |
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285 | C<eio_cancel>: |
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286 | |
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287 | =over 4 |
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288 | |
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289 | =item eio_cancel (eio_req *req) |
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290 | |
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291 | Cancel the request (and all its subrequests). If the request is currently |
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292 | executing it might still continue to execute, and in other cases it might |
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293 | still take a while till the request is cancelled. |
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294 | |
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295 | Even if cancelled, the finish callback will still be invoked - the |
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296 | callbacks of all cancellable requests need to check whether the request |
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297 | has been cancelled by calling C<EIO_CANCELLED (req)>: |
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298 | |
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299 | static int |
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300 | my_eio_cb (eio_req *req) |
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301 | { |
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302 | if (EIO_CANCELLED (req)) |
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303 | return 0; |
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304 | } |
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305 | |
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306 | In addition, cancelled requests will I<either> have C<< req->result >> |
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307 | set to C<-1> and C<errno> to C<ECANCELED>, or I<otherwise> they were |
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308 | successfully executed, despite being cancelled (e.g. when they have |
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309 | already been executed at the time they were cancelled). |
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310 | |
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311 | C<EIO_CANCELLED> is still true for requests that have successfully |
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312 | executed, as long as C<eio_cancel> was called on them at some point. |
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313 | |
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314 | =back |
222 | |
315 | |
223 | =head2 AVAILABLE REQUESTS |
316 | =head2 AVAILABLE REQUESTS |
224 | |
317 | |
225 | The following request functions are available. I<All> of them return the |
318 | 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 |
319 | C<eio_req *> on success and C<0> on failure, and I<all> of them have the |
… | |
… | |
322 | free (target); |
415 | free (target); |
323 | } |
416 | } |
324 | |
417 | |
325 | =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) |
326 | |
419 | |
327 | Similar to the realpath libc function, but unlike that one, result is |
420 | Similar to the realpath libc function, but unlike that one, C<< |
328 | C<0> on failure and the length of the returned path in C<ptr2> - this is |
421 | req->result >> is C<-1> on failure. On success, the result is the length |
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422 | of the returned path in C<ptr2> (which is I<NOT> 0-terminated) - this is |
329 | similar to readlink. |
423 | similar to readlink. |
330 | |
424 | |
331 | =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) |
332 | |
426 | |
333 | =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) |
… | |
… | |
335 | =item eio_fstat (int fd, int pri, eio_cb cb, void *data) |
429 | =item eio_fstat (int fd, int pri, eio_cb cb, void *data) |
336 | |
430 | |
337 | Stats a file - if C<< req->result >> indicates success, then you can |
431 | Stats a file - if C<< req->result >> indicates success, then you can |
338 | access the C<struct stat>-like structure via C<< req->ptr2 >>: |
432 | access the C<struct stat>-like structure via C<< req->ptr2 >>: |
339 | |
433 | |
340 | EIO_STRUCT_STAT *statdata = (EIO_STRUCT_STAT *)req->ptr2; |
434 | EIO_STRUCT_STAT *statdata = (EIO_STRUCT_STAT *)req->ptr2; |
341 | |
435 | |
342 | =item eio_statvfs (const char *path, int pri, eio_cb cb, void *data) |
436 | =item eio_statvfs (const char *path, int pri, eio_cb cb, void *data) |
343 | |
437 | |
344 | =item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data) |
438 | =item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data) |
345 | |
439 | |
346 | Stats a filesystem - if C<< req->result >> indicates success, then you can |
440 | Stats a filesystem - if C<< req->result >> indicates success, then you can |
347 | access the C<struct statvfs>-like structure via C<< req->ptr2 >>: |
441 | access the C<struct statvfs>-like structure via C<< req->ptr2 >>: |
348 | |
442 | |
349 | EIO_STRUCT_STATVFS *statdata = (EIO_STRUCT_STATVFS *)req->ptr2; |
443 | EIO_STRUCT_STATVFS *statdata = (EIO_STRUCT_STATVFS *)req->ptr2; |
350 | |
444 | |
351 | =back |
445 | =back |
352 | |
446 | |
353 | =head3 READING DIRECTORIES |
447 | =head3 READING DIRECTORIES |
354 | |
448 | |
355 | Reading directories sounds simple, but can be rather demanding, especially |
449 | Reading directories sounds simple, but can be rather demanding, especially |
356 | if you want to do stuff such as traversing a diretcory hierarchy or |
450 | if you want to do stuff such as traversing a directory hierarchy or |
357 | processing all files in a directory. Libeio can assist thess complex tasks |
451 | processing all files in a directory. Libeio can assist these complex tasks |
358 | with it's C<eio_readdir> call. |
452 | with it's C<eio_readdir> call. |
359 | |
453 | |
360 | =over 4 |
454 | =over 4 |
361 | |
455 | |
362 | =item eio_readdir (const char *path, int flags, int pri, eio_cb cb, void *data) |
456 | =item eio_readdir (const char *path, int flags, int pri, eio_cb cb, void *data) |
… | |
… | |
394 | |
488 | |
395 | If this flag is specified, then, in addition to the names in C<ptr2>, |
489 | 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 |
490 | also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct |
397 | eio_dirent> looks like this: |
491 | eio_dirent> looks like this: |
398 | |
492 | |
399 | struct eio_dirent |
493 | struct eio_dirent |
400 | { |
494 | { |
401 | int nameofs; /* offset of null-terminated name string in (char *)req->ptr2 */ |
495 | int nameofs; /* offset of null-terminated name string in (char *)req->ptr2 */ |
402 | unsigned short namelen; /* size of filename without trailing 0 */ |
496 | unsigned short namelen; /* size of filename without trailing 0 */ |
403 | unsigned char type; /* one of EIO_DT_* */ |
497 | unsigned char type; /* one of EIO_DT_* */ |
404 | signed char score; /* internal use */ |
498 | signed char score; /* internal use */ |
405 | ino_t inode; /* the inode number, if available, otherwise unspecified */ |
499 | ino_t inode; /* the inode number, if available, otherwise unspecified */ |
406 | }; |
500 | }; |
407 | |
501 | |
408 | The only members you normally would access are C<nameofs>, which is the |
502 | 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>. |
503 | byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>. |
410 | |
504 | |
411 | C<type> can be one of: |
505 | C<type> can be one of: |
… | |
… | |
454 | When this flag is specified, then the names will be returned in an order |
548 | When this flag is specified, then the names will be returned in an order |
455 | suitable for stat()'ing each one. That is, when you plan to stat() |
549 | suitable for stat()'ing each one. That is, when you plan to stat() |
456 | all files in the given directory, then the returned order will likely |
550 | all files in the given directory, then the returned order will likely |
457 | be fastest. |
551 | be fastest. |
458 | |
552 | |
459 | If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then |
553 | If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then the |
460 | the likely dirs come first, resulting in a less optimal stat order. |
554 | likely directories come first, resulting in a less optimal stat order. |
461 | |
555 | |
462 | =item EIO_READDIR_FOUND_UNKNOWN |
556 | =item EIO_READDIR_FOUND_UNKNOWN |
463 | |
557 | |
464 | This flag should not be specified when calling C<eio_readdir>. Instead, |
558 | This flag should not be specified when calling C<eio_readdir>. Instead, |
465 | it is being set by C<eio_readdir> (you can access the C<flags> via C<< |
559 | it is being set by C<eio_readdir> (you can access the C<flags> via C<< |
466 | req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The |
560 | req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The |
467 | absense of this flag therefore indicates that all C<type>'s are known, |
561 | absence of this flag therefore indicates that all C<type>'s are known, |
468 | which can be used to speed up some algorithms. |
562 | which can be used to speed up some algorithms. |
469 | |
563 | |
470 | A typical use case would be to identify all subdirectories within a |
564 | A typical use case would be to identify all subdirectories within a |
471 | directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If |
565 | directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If |
472 | then this flag is I<NOT> set, then all the entries at the beginning of the |
566 | then this flag is I<NOT> set, then all the entries at the beginning of the |
… | |
… | |
502 | =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) |
503 | |
597 | |
504 | 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 |
505 | emulated by simply reading the data (currently in 64kiB chunks). |
599 | emulated by simply reading the data (currently in 64kiB chunks). |
506 | |
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 |
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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 |
|
|
606 | syscall with a negative C<fd> argument and checking for C<-1/ENOSYS>. |
|
|
607 | |
507 | =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) |
508 | |
609 | |
509 | 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 |
510 | as calling C<fdatasync>. |
611 | as calling C<fdatasync>. |
511 | |
612 | |
512 | 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>, |
513 | 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 |
|
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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). |
514 | |
624 | |
515 | =back |
625 | =back |
516 | |
626 | |
517 | =head3 LIBEIO-SPECIFIC REQUESTS |
627 | =head3 LIBEIO-SPECIFIC REQUESTS |
518 | |
628 | |
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560 | |
670 | |
561 | eio_custom (my_open, 0, my_open_done, "/etc/passwd"); |
671 | eio_custom (my_open, 0, my_open_done, "/etc/passwd"); |
562 | |
672 | |
563 | =item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data) |
673 | =item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data) |
564 | |
674 | |
565 | This is a a request that takes C<delay> seconds to execute, but otherwise |
675 | This is a request that takes C<delay> seconds to execute, but otherwise |
566 | does nothing - it simply puts one of the worker threads to sleep for this |
676 | does nothing - it simply puts one of the worker threads to sleep for this |
567 | long. |
677 | long. |
568 | |
678 | |
569 | This request can be used to artificially increase load, e.g. for debugging |
679 | This request can be used to artificially increase load, e.g. for debugging |
570 | or benchmarking reasons. |
680 | or benchmarking reasons. |
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586 | There are two primary use cases for this: a) bundle many requests into a |
696 | There are two primary use cases for this: a) bundle many requests into a |
587 | single, composite, request with a definite callback and the ability to |
697 | single, composite, request with a definite callback and the ability to |
588 | cancel the whole request with its subrequests and b) limiting the number |
698 | cancel the whole request with its subrequests and b) limiting the number |
589 | of "active" requests. |
699 | of "active" requests. |
590 | |
700 | |
591 | Further below you will find more dicussion of these topics - first follows |
701 | Further below you will find more discussion of these topics - first |
592 | the reference section detailing the request generator and other methods. |
702 | follows the reference section detailing the request generator and other |
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703 | methods. |
593 | |
704 | |
594 | =over 4 |
705 | =over 4 |
595 | |
706 | |
596 | =item eio_grp (eio_cb cb, void *data) |
707 | =item eio_req *grp = eio_grp (eio_cb cb, void *data) |
597 | |
708 | |
598 | Creates and submits a group request. |
709 | Creates, submits and returns a group request. Note that it doesn't have a |
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710 | priority, unlike all other requests. |
599 | |
711 | |
600 | =back |
712 | =item eio_grp_add (eio_req *grp, eio_req *req) |
601 | |
713 | |
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714 | Adds a request to the request group. |
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715 | |
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716 | =item eio_grp_cancel (eio_req *grp) |
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717 | |
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718 | Cancels all requests I<in> the group, but I<not> the group request |
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719 | itself. You can cancel the group request I<and> all subrequests via a |
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720 | normal C<eio_cancel> call. |
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721 | |
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722 | =back |
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723 | |
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724 | =head4 GROUP REQUEST LIFETIME |
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725 | |
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726 | Left alone, a group request will instantly move to the pending state and |
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727 | will be finished at the next call of C<eio_poll>. |
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728 | |
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729 | The usefulness stems from the fact that, if a subrequest is added to a |
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730 | group I<before> a call to C<eio_poll>, via C<eio_grp_add>, then the group |
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731 | will not finish until all the subrequests have finished. |
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732 | |
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733 | So the usage cycle of a group request is like this: after it is created, |
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734 | you normally instantly add a subrequest. If none is added, the group |
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735 | request will finish on it's own. As long as subrequests are added before |
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736 | the group request is finished it will be kept from finishing, that is the |
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737 | callbacks of any subrequests can, in turn, add more requests to the group, |
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738 | and as long as any requests are active, the group request itself will not |
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739 | finish. |
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740 | |
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741 | =head4 CREATING COMPOSITE REQUESTS |
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742 | |
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743 | Imagine you wanted to create an C<eio_load> request that opens a file, |
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744 | reads it and closes it. This means it has to execute at least three eio |
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745 | requests, but for various reasons it might be nice if that request looked |
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746 | like any other eio request. |
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747 | |
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748 | This can be done with groups: |
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749 | |
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750 | =over 4 |
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751 | |
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752 | =item 1) create the request object |
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753 | |
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754 | Create a group that contains all further requests. This is the request you |
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755 | can return as "the load request". |
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756 | |
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757 | =item 2) open the file, maybe |
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758 | |
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759 | Next, open the file with C<eio_open> and add the request to the group |
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760 | request and you are finished setting up the request. |
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761 | |
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762 | If, for some reason, you cannot C<eio_open> (path is a null ptr?) you |
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763 | can set C<< grp->result >> to C<-1> to signal an error and let the group |
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764 | request finish on its own. |
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765 | |
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766 | =item 3) open callback adds more requests |
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767 | |
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768 | In the open callback, if the open was not successful, copy C<< |
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769 | req->errorno >> to C<< grp->errorno >> and set C<< grp->result >> to |
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770 | C<-1> to signal an error. |
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771 | |
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772 | Otherwise, malloc some memory or so and issue a read request, adding the |
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773 | read request to the group. |
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774 | |
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775 | =item 4) continue issuing requests till finished |
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776 | |
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777 | In the read callback, check for errors and possibly continue with |
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778 | C<eio_close> or any other eio request in the same way. |
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779 | |
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780 | As soon as no new requests are added, the group request will finish. Make |
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781 | sure you I<always> set C<< grp->result >> to some sensible value. |
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782 | |
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783 | =back |
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784 | |
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785 | =head4 REQUEST LIMITING |
602 | |
786 | |
603 | |
787 | |
604 | #TODO |
788 | #TODO |
605 | |
789 | |
606 | /*****************************************************************************/ |
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607 | /* groups */ |
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608 | |
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609 | eio_req *eio_grp (eio_cb cb, void *data); |
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610 | void eio_grp_feed (eio_req *grp, void (*feed)(eio_req *req), int limit); |
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611 | void eio_grp_limit (eio_req *grp, int limit); |
790 | 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 */ |
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614 | |
791 | |
615 | |
792 | |
616 | =back |
793 | =back |
617 | |
794 | |
618 | |
795 | |
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624 | =head1 ANATOMY AND LIFETIME OF AN EIO REQUEST |
801 | =head1 ANATOMY AND LIFETIME OF AN EIO REQUEST |
625 | |
802 | |
626 | A request is represented by a structure of type C<eio_req>. To initialise |
803 | A request is represented by a structure of type C<eio_req>. To initialise |
627 | it, clear it to all zero bytes: |
804 | it, clear it to all zero bytes: |
628 | |
805 | |
629 | eio_req req; |
806 | eio_req req; |
630 | |
807 | |
631 | memset (&req, 0, sizeof (req)); |
808 | memset (&req, 0, sizeof (req)); |
632 | |
809 | |
633 | A more common way to initialise a new C<eio_req> is to use C<calloc>: |
810 | A more common way to initialise a new C<eio_req> is to use C<calloc>: |
634 | |
811 | |
635 | eio_req *req = calloc (1, sizeof (*req)); |
812 | eio_req *req = calloc (1, sizeof (*req)); |
636 | |
813 | |
637 | In either case, libeio neither allocates, initialises or frees the |
814 | In either case, libeio neither allocates, initialises or frees the |
638 | C<eio_req> structure for you - it merely uses it. |
815 | C<eio_req> structure for you - it merely uses it. |
639 | |
816 | |
640 | zero |
817 | zero |
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658 | for example, in interactive programs, you might want to limit this time to |
835 | for example, in interactive programs, you might want to limit this time to |
659 | C<0.01> seconds or so. |
836 | C<0.01> seconds or so. |
660 | |
837 | |
661 | Note that: |
838 | Note that: |
662 | |
839 | |
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840 | =over 4 |
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841 | |
663 | a) libeio doesn't know how long your request callbacks take, so the time |
842 | =item a) libeio doesn't know how long your request callbacks take, so the |
664 | spent in C<eio_poll> is up to one callback invocation longer then this |
843 | time spent in C<eio_poll> is up to one callback invocation longer then |
665 | interval. |
844 | this interval. |
666 | |
845 | |
667 | b) this is implemented by calling C<gettimeofday> after each request, |
846 | =item b) this is implemented by calling C<gettimeofday> after each |
668 | which can be costly. |
847 | request, which can be costly. |
669 | |
848 | |
670 | c) at least one request will be handled. |
849 | =item c) at least one request will be handled. |
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850 | |
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851 | =back |
671 | |
852 | |
672 | =item eio_set_max_poll_reqs (unsigned int nreqs) |
853 | =item eio_set_max_poll_reqs (unsigned int nreqs) |
673 | |
854 | |
674 | When C<nreqs> is non-zero, then C<eio_poll> will not handle more than |
855 | When C<nreqs> is non-zero, then C<eio_poll> will not handle more than |
675 | C<nreqs> requests per invocation. This is a less costly way to limit the |
856 | C<nreqs> requests per invocation. This is a less costly way to limit the |
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745 | 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 |
746 | 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> |
747 | requests, you might want to increase this. |
928 | requests, you might want to increase this. |
748 | |
929 | |
749 | 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 |
750 | 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 |
751 | 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 |
752 | 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 |
753 | stack size. |
934 | stack size. |
754 | |
935 | |
755 | =back |
936 | =back |