[ViewVC] Diff of: cvs/libeio/eio.pod

Comparing libeio/eio.pod (file contents):
Revision 1.7 by root, Sun Jun 5 22:44:30 2011 UTC vs.
Revision 1.36 by root, Sun Jan 24 16:36:20 2016 UTC

…		…
25	similar functions, as well as less rarely ones such as C<mknod>, C<futime>	25	similar functions, as well as less rarely ones such as C<mknod>, C<futime>
26	or C<readlink>.	26	or C<readlink>.
27		27
28	It also offers wrappers around C<sendfile> (Solaris, Linux, HP-UX and	28	It also offers wrappers around C<sendfile> (Solaris, Linux, HP-UX and
29	FreeBSD, with emulation on other platforms) and C<readahead> (Linux, with	29	FreeBSD, with emulation on other platforms) and C<readahead> (Linux, with
30	emulation elsewhere>).	30	emulation elsewhere).
31		31
32	The goal is to enable you to write fully non-blocking programs. For	32	The goal is to enable you to write fully non-blocking programs. For
33	example, in a game server, you would not want to freeze for a few seconds	33	example, in a game server, you would not want to freeze for a few seconds
34	just because the server is running a backup and you happen to call	34	just because the server is running a backup and you happen to call
35	C<readdir>.	35	C<readdir>.
…		…
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
		51	considerably. Specifically, only async-safe functions can be called after
		52	fork. Libeio uses pthreads, so this applies, and makes using fork hard for
		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
56	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	libeio queue.
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
		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.
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.
		86
		87	There is currently no way to change these callbacks later, or to
		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",
…		…
97	This callback is invoked when libeio detects that all pending requests	104	This callback is invoked when libeio detects that all pending requests
98	have been handled. It is "edge-triggered", that is, it will only be	105	have been handled. It is "edge-triggered", that is, it will only be
99	called once after C<want_poll>. To put it differently, C<want_poll> and	106	called once after C<want_poll>. To put it differently, C<want_poll> and
100	C<done_poll> are invoked in pairs: after C<want_poll> you have to call	107	C<done_poll> are invoked in pairs: after C<want_poll> you have to call
101	C<eio_poll ()> until either C<eio_poll> indicates that everything has been	108	C<eio_poll ()> until either C<eio_poll> indicates that everything has been
102	handled or C<done_poll> has been called, which signals the same.	109	handled or C<done_poll> has been called, which signals the same - only one
		110	method is needed.
103		111
104	Note that C<eio_poll> might return after C<done_poll> and C<want_poll>	112	Note that C<eio_poll> might return after C<done_poll> and C<want_poll>
105	have been called again, so watch out for races in your code.	113	have been called again, so watch out for races in your code.
106		114
		115	It is quite common to have an empty C<done_call> callback and only use
		116	the return value from C<eio_poll>, or, when C<eio_poll> is configured to
		117	handle all outstanding replies, it's enough to call C<eio_poll> once.
		118
107	As with C<want_poll>, this callback is called while locks are being held,	119	As with C<want_poll>, this callback is called while locks are being held,
108	so you I<must not call any libeio functions form within this callback>.	120	so you I<must not call any libeio functions from within this callback>.
109		121
110	=item int eio_poll ()	122	=item int eio_poll ()
111		123
112	This function has to be called whenever there are pending requests that	124	This function has to be called whenever there are pending requests that
113	need finishing. You usually call this after C<want_poll> has indicated	125	need finishing. You usually call this after C<want_poll> has indicated
…		…
124	=back	136	=back
125		137
126	For libev, you would typically use an C<ev_async> watcher: the	138	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	139	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	140	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	141	()>.
130	all requests have been handled yet). The race is taken care of because	142
131	libev resets/rearms the async watcher before calling your callback,	143	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)	144	(i.e. it returns C<-1>) then you should start an idle watcher that calls
133	spurious wake-ups, but is generally harmless.	145	C<eio_poll> until it returns something C<!= -1>.
		146
		147	A full-featured connector between libeio and libev would look as follows
		148	(if C<eio_poll> is handling all requests, it can of course be simplified a
		149	lot by removing the idle watcher logic):
		150
		151	static struct ev_loop *loop;
		152	static ev_idle repeat_watcher;
		153	static ev_async ready_watcher;
		154
		155	/* idle watcher callback, only used when eio_poll */
		156	/* didn't handle all results in one call */
		157	static void
		158	repeat (EV_P_ ev_idle *w, int revents)
		159	{
		160	if (eio_poll () != -1)
		161	ev_idle_stop (EV_A_ w);
		162	}
		163
		164	/* eio has some results, process them */
		165	static void
		166	ready (EV_P_ ev_async *w, int revents)
		167	{
		168	if (eio_poll () == -1)
		169	ev_idle_start (EV_A_ &repeat_watcher);
		170	}
		171
		172	/* wake up the event loop */
		173	static void
		174	want_poll (void)
		175	{
		176	ev_async_send (loop, &ready_watcher)
		177	}
		178
		179	void
		180	my_init_eio ()
		181	{
		182	loop = EV_DEFAULT;
		183
		184	ev_idle_init (&repeat_watcher, repeat);
		185	ev_async_init (&ready_watcher, ready);
		186	ev_async_start (loop, &watcher);
		187
		188	eio_init (want_poll, 0);
		189	}
134		190
135	For most other event loops, you would typically use a pipe - the event	191	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	192	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	193	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	194	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
140	your callback again and again until the byte has been read (as the pipe
141	read callback does not read it, only C<done_poll>).
142
143	=head2 CONFIGURATION
144
145	The functions in this section can sometimes be useful, but the default
146	configuration will do in most case, so you should skip this section on
147	first reading.
148
149	=over 4
150
151	=item eio_set_max_poll_time (eio_tstamp nseconds)
152
153	This causes C<eio_poll ()> to return after it has detected that it was
154	running for C<nsecond> seconds or longer (this number can be fractional).
155
156	This can be used to limit the amount of time spent handling eio requests,
157	for example, in interactive programs, you might want to limit this time to
158	C<0.01> seconds or so.
159
160	Note that:
161
162	a) libeio doesn't know how long your request callbacks take, so the time
163	spent in C<eio_poll> is up to one callback invocation longer then this
164	interval.
165
166	b) this is implemented by calling C<gettimeofday> after each request,
167	which can be costly.
168
169	c) at least one request will be handled.
170
171	=item eio_set_max_poll_reqs (unsigned int nreqs)
172
173	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than
174	C<nreqs> requests per invocation. This is a less costly way to limit the
175	amount of work done by C<eio_poll> then setting a time limit.
176
177	If you know your callbacks are generally fast, you could use this to
178	encourage interactiveness in your programs by setting it to C<10>, C<100>
179	or even C<1000>.
180
181	=item eio_set_min_parallel (unsigned int nthreads)
182
183	Make sure libeio can handle at least this many requests in parallel. It
184	might be able handle more.
185
186	=item eio_set_max_parallel (unsigned int nthreads)
187
188	Set the maximum number of threads that libeio will spawn.
189
190	=item eio_set_max_idle (unsigned int nthreads)
191
192	Libeio uses threads internally to handle most requests, and will start and stop threads on demand.
193
194	This call can be used to limit the number of idle threads (threads without
195	work to do): libeio will keep some threads idle in preparation for more
196	requests, but never longer than C<nthreads> threads.
197
198	In addition to this, libeio will also stop threads when they are idle for
199	a few seconds, regardless of this setting.
200
201	=item unsigned int eio_nthreads ()
202
203	Return the number of worker threads currently running.
204
205	=item unsigned int eio_nreqs ()
206
207	Return the number of requests currently handled by libeio. This is the
208	total number of requests that have been submitted to libeio, but not yet
209	destroyed.
210
211	=item unsigned int eio_nready ()
212
213	Returns the number of ready requests, i.e. requests that have been
214	submitted but have not yet entered the execution phase.
215
216	=item unsigned int eio_npending ()
217
218	Returns the number of pending requests, i.e. requests that have been
219	executed and have results, but have not been finished yet by a call to
220	C<eio_poll>).	195	C<eio_poll>.
221		196
222	=back	197	You don't have to take special care in the case C<eio_poll> doesn't handle
		198	all requests, as the done callback will not be invoked, so the event loop
		199	will still signal readiness for the pipe until I<all> results have been
		200	processed.
223		201
224		202
225	=head1 HIGH LEVEL REQUEST API	203	=head1 HIGH LEVEL REQUEST API
226		204
227	Libeio has both a high-level API, which consists of calling a request	205	Libeio has both a high-level API, which consists of calling a request
…		…
234		212
235	You submit a request by calling the relevant C<eio_TYPE> function with the	213	You submit a request by calling the relevant C<eio_TYPE> function with the
236	required parameters, a callback of type C<int (eio_cb)(eio_req req)>	214	required parameters, a callback of type C<int (eio_cb)(eio_req req)>
237	(called C<eio_cb> below) and a freely usable C<void *data> argument.	215	(called C<eio_cb> below) and a freely usable C<void *data> argument.
238		216
239	The return value will either be 0	217	The return value will either be 0, in case something went really wrong
		218	(which can basically only happen on very fatal errors, such as C<malloc>
		219	returning 0, which is rather unlikely), or a pointer to the newly-created
		220	and submitted C<eio_req *>.
240		221
241	The callback will be called with an C<eio_req *> which contains the	222	The callback will be called with an C<eio_req *> which contains the
242	results of the request. The members you can access inside that structure	223	results of the request. The members you can access inside that structure
243	vary from request to request, except for:	224	vary from request to request, except for:
244		225
…		…
256	=item C<void *data>	237	=item C<void *data>
257		238
258	The C<void *data> member simply stores the value of the C<data> argument.	239	The C<void *data> member simply stores the value of the C<data> argument.
259		240
260	=back	241	=back
		242
		243	Members not explicitly described as accessible must not be
		244	accessed. Specifically, there is no guarantee that any members will still
		245	have the value they had when the request was submitted.
261		246
262	The return value of the callback is normally C<0>, which tells libeio to	247	The return value of the callback is normally C<0>, which tells libeio to
263	continue normally. If a callback returns a nonzero value, libeio will	248	continue normally. If a callback returns a nonzero value, libeio will
264	stop processing results (in C<eio_poll>) and will return the value to its	249	stop processing results (in C<eio_poll>) and will return the value to its
265	caller.	250	caller.
266		251
267	Memory areas passed to libeio must stay valid as long as a request	252	Memory areas passed to libeio wrappers must stay valid as long as a
268	executes, with the exception of paths, which are being copied	253	request executes, with the exception of paths, which are being copied
269	internally. Any memory libeio itself allocates will be freed after the	254	internally. Any memory libeio itself allocates will be freed after the
270	finish callback has been called. If you want to manage all memory passed	255	finish callback has been called. If you want to manage all memory passed
271	to libeio yourself you can use the low-level API.	256	to libeio yourself you can use the low-level API.
272		257
273	For example, to open a file, you could do this:	258	For example, to open a file, you could do this:
…		…
291	}	276	}
292		277
293	/* the first three arguments are passed to open(2) */	278	/* the first three arguments are passed to open(2) */
294	/* the remaining are priority, callback and data */	279	/* the remaining are priority, callback and data */
295	if (!eio_open ("/etc/passwd", O_RDONLY, 0, 0, file_open_done, 0))	280	if (!eio_open ("/etc/passwd", O_RDONLY, 0, 0, file_open_done, 0))
296	abort (); /* something ent wrong, we will all die!!! */	281	abort (); /* something went wrong, we will all die!!! */
297		282
298	Note that you additionally need to call C<eio_poll> when the C<want_cb>	283	Note that you additionally need to call C<eio_poll> when the C<want_cb>
299	indicates that requests are ready to be processed.	284	indicates that requests are ready to be processed.
		285
		286	=head2 CANCELLING REQUESTS
		287
		288	Sometimes the need for a request goes away before the request is
		289	finished. In that case, one can cancel the request by a call to
		290	C<eio_cancel>:
		291
		292	=over 4
		293
		294	=item eio_cancel (eio_req *req)
		295
		296	Cancel the request (and all its subrequests). If the request is currently
		297	executing it might still continue to execute, and in other cases it might
		298	still take a while till the request is cancelled.
		299
		300	When cancelled, the finish callback will not be invoked.
		301
		302	C<EIO_CANCELLED> is still true for requests that have successfully
		303	executed, as long as C<eio_cancel> was called on them at some point.
		304
		305	=back
300		306
301	=head2 AVAILABLE REQUESTS	307	=head2 AVAILABLE REQUESTS
302		308
303	The following request functions are available. I<All> of them return the	309	The following request functions are available. I<All> of them return the
304	C<eio_req *> on success and C<0> on failure, and I<all> of them have the	310	C<eio_req *> on success and C<0> on failure, and I<all> of them have the
…		…
307	custom data value as C<data>.	313	custom data value as C<data>.
308		314
309	=head3 POSIX API WRAPPERS	315	=head3 POSIX API WRAPPERS
310		316
311	These requests simply wrap the POSIX call of the same name, with the same	317	These requests simply wrap the POSIX call of the same name, with the same
312	arguments:	318	arguments. If a function is not implemented by the OS and cannot be emulated
		319	in some way, then all of these return C<-1> and set C<errorno> to C<ENOSYS>.
313		320
314	=over 4	321	=over 4
315		322
316	=item eio_open (const char path, int flags, mode_t mode, int pri, eio_cb cb, void data)	323	=item eio_open (const char path, int flags, mode_t mode, int pri, eio_cb cb, void data)
317		324
		325	=item eio_truncate (const char path, off_t offset, int pri, eio_cb cb, void data)
		326
		327	=item eio_chown (const char path, uid_t uid, gid_t gid, int pri, eio_cb cb, void data)
		328
		329	=item eio_chmod (const char path, mode_t mode, int pri, eio_cb cb, void data)
		330
		331	=item eio_mkdir (const char path, mode_t mode, int pri, eio_cb cb, void data)
		332
		333	=item eio_rmdir (const char path, int pri, eio_cb cb, void data)
		334
		335	=item eio_unlink (const char path, int pri, eio_cb cb, void data)
		336
318	=item eio_utime (const char path, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void data)	337	=item eio_utime (const char path, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void data)
319		338
320	=item eio_truncate (const char path, off_t offset, int pri, eio_cb cb, void data)
321
322	=item eio_chown (const char path, uid_t uid, gid_t gid, int pri, eio_cb cb, void data)
323
324	=item eio_chmod (const char path, mode_t mode, int pri, eio_cb cb, void data)
325
326	=item eio_mkdir (const char path, mode_t mode, int pri, eio_cb cb, void data)
327
328	=item eio_rmdir (const char path, int pri, eio_cb cb, void data)
329
330	=item eio_unlink (const char path, int pri, eio_cb cb, void data)
331
332	=item eio_readlink (const char path, int pri, eio_cb cb, void data) /* result=ptr2 allocated dynamically */
333
334	=item eio_stat (const char path, int pri, eio_cb cb, void data) /* stat buffer=ptr2 allocated dynamically */
335
336	=item eio_lstat (const char path, int pri, eio_cb cb, void data) /* stat buffer=ptr2 allocated dynamically */
337
338	=item eio_statvfs (const char path, int pri, eio_cb cb, void data) /* stat buffer=ptr2 allocated dynamically */
339
340	=item eio_mknod (const char path, mode_t mode, dev_t dev, int pri, eio_cb cb, void data)	339	=item eio_mknod (const char path, mode_t mode, dev_t dev, int pri, eio_cb cb, void data)
341		340
342	=item eio_link (const char path, const char new_path, int pri, eio_cb cb, void *data)	341	=item eio_link (const char path, const char new_path, int pri, eio_cb cb, void *data)
343		342
344	=item eio_symlink (const char path, const char new_path, int pri, eio_cb cb, void *data)	343	=item eio_symlink (const char path, const char new_path, int pri, eio_cb cb, void *data)
345		344
346	=item eio_rename (const char path, const char new_path, int pri, eio_cb cb, void *data)	345	=item eio_rename (const char path, const char new_path, int pri, eio_cb cb, void *data)
347		346
348	=item eio_msync (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
349
350	=item eio_mlock (void addr, size_t length, int pri, eio_cb cb, void data)	347	=item eio_mlock (void addr, size_t length, int pri, eio_cb cb, void data)
351
352	=item eio_mlockall (int flags, int pri, eio_cb cb, void *data)
353		348
354	=item eio_close (int fd, int pri, eio_cb cb, void *data)	349	=item eio_close (int fd, int pri, eio_cb cb, void *data)
355		350
356	=item eio_sync (int pri, eio_cb cb, void *data)	351	=item eio_sync (int pri, eio_cb cb, void *data)
357		352
…		…
386		381
387	Not surprisingly, pread and pwrite are not thread-safe on Darwin (OS/X),	382	Not surprisingly, pread and pwrite are not thread-safe on Darwin (OS/X),
388	so it is advised not to submit multiple requests on the same fd on this	383	so it is advised not to submit multiple requests on the same fd on this
389	horrible pile of garbage.	384	horrible pile of garbage.
390		385
		386	=item eio_mlockall (int flags, int pri, eio_cb cb, void *data)
		387
		388	Like C<mlockall>, but the flag value constants are called
		389	C<EIO_MCL_CURRENT> and C<EIO_MCL_FUTURE>.
		390
		391	=item eio_msync (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
		392
		393	Just like msync, except that the flag values are called C<EIO_MS_ASYNC>,
		394	C<EIO_MS_INVALIDATE> and C<EIO_MS_SYNC>.
		395
		396	=item eio_readlink (const char path, int pri, eio_cb cb, void data)
		397
		398	If successful, the path read by C<readlink(2)> can be accessed via C<<
		399	req->ptr2 >> and is I<NOT> null-terminated, with the length specified as
		400	C<< req->result >>.
		401
		402	if (req->result >= 0)
		403	{
		404	char target = strndup ((char )req->ptr2, req->result);
		405
		406	free (target);
		407	}
		408
		409	=item eio_realpath (const char path, int pri, eio_cb cb, void data)
		410
		411	Similar to the realpath libc function, but unlike that one, C<<
		412	req->result >> is C<-1> on failure. On success, the result is the length
		413	of the returned path in C<ptr2> (which is I<NOT> 0-terminated) - this is
		414	similar to readlink.
		415
		416	=item eio_stat (const char path, int pri, eio_cb cb, void data)
		417
		418	=item eio_lstat (const char path, int pri, eio_cb cb, void data)
		419
391	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)	420	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)
392		421
393	Stats a file - if C<< req->result >> indicates success, then you can	422	Stats a file - if C<< req->result >> indicates success, then you can
394	access the C<struct stat>-like structure via C<< req->ptr2 >>:	423	access the C<struct stat>-like structure via C<< req->ptr2 >>:
395		424
396	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;	425	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
397		426
398	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void data) / stat buffer=ptr2 allocated dynamically */	427	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)
		428
		429	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)
399		430
400	Stats a filesystem - if C<< req->result >> indicates success, then you can	431	Stats a filesystem - if C<< req->result >> indicates success, then you can
401	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:	432	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
402		433
403	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;	434	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
404		435
405	=back	436	=back
406		437
407	=head3 READING DIRECTORIES	438	=head3 READING DIRECTORIES
408		439
409	Reading directories sounds simple, but can be rather demanding, especially	440	Reading directories sounds simple, but can be rather demanding, especially
410	if you want to do stuff such as traversing a diretcory hierarchy or	441	if you want to do stuff such as traversing a directory hierarchy or
411	processing all files in a directory. Libeio can assist thess complex tasks	442	processing all files in a directory. Libeio can assist these complex tasks
412	with it's C<eio_readdir> call.	443	with it's C<eio_readdir> call.
413		444
414	=over 4	445	=over 4
415		446
416	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)	447	=item eio_readdir (const char path, int flags, int pri, eio_cb cb, void data)
…		…
419	(via the C<opendir>, C<readdir> and C<closedir> calls) and returns either	450	(via the C<opendir>, C<readdir> and C<closedir> calls) and returns either
420	the names or an array of C<struct eio_dirent>, depending on the C<flags>	451	the names or an array of C<struct eio_dirent>, depending on the C<flags>
421	argument.	452	argument.
422		453
423	The C<< req->result >> indicates either the number of files found, or	454	The C<< req->result >> indicates either the number of files found, or
424	C<-1> on error. On success, zero-terminated names can be found as C<< req->ptr2 >>,	455	C<-1> on error. On success, null-terminated names can be found as C<< req->ptr2 >>,
425	and C<struct eio_dirents>, if requested by C<flags>, can be found via C<<	456	and C<struct eio_dirents>, if requested by C<flags>, can be found via C<<
426	req->ptr1 >>.	457	req->ptr1 >>.
427		458
428	Here is an example that prints all the names:	459	Here is an example that prints all the names:
429		460
…		…
448		479
449	If this flag is specified, then, in addition to the names in C<ptr2>,	480	If this flag is specified, then, in addition to the names in C<ptr2>,
450	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct	481	also an array of C<struct eio_dirent> is returned, in C<ptr1>. A C<struct
451	eio_dirent> looks like this:	482	eio_dirent> looks like this:
452		483
453	struct eio_dirent	484	struct eio_dirent
454	{	485	{
455	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /	486	int nameofs; /* offset of null-terminated name string in (char )req->ptr2 /
456	unsigned short namelen; /* size of filename without trailing 0 */	487	unsigned short namelen; /* size of filename without trailing 0 */
457	unsigned char type; /* one of EIO_DT_* */	488	unsigned char type; /* one of EIO_DT_* */
458	signed char score; /* internal use */	489	signed char score; /* internal use */
459	ino_t inode; /* the inode number, if available, otherwise unspecified */	490	ino_t inode; /* the inode number, if available, otherwise unspecified */
460	};	491	};
461		492
462	The only members you normally would access are C<nameofs>, which is the	493	The only members you normally would access are C<nameofs>, which is the
463	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.	494	byte-offset from C<ptr2> to the start of the name, C<namelen> and C<type>.
464		495
465	C<type> can be one of:	496	C<type> can be one of:
…		…
508	When this flag is specified, then the names will be returned in an order	539	When this flag is specified, then the names will be returned in an order
509	suitable for stat()'ing each one. That is, when you plan to stat()	540	suitable for stat()'ing each one. That is, when you plan to stat()
510	all files in the given directory, then the returned order will likely	541	all files in the given directory, then the returned order will likely
511	be fastest.	542	be fastest.
512		543
513	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then	544	If both this flag and C<EIO_READDIR_DIRS_FIRST> are specified, then the
514	the likely dirs come first, resulting in a less optimal stat order.	545	likely directories come first, resulting in a less optimal stat order.
515		546
516	=item EIO_READDIR_FOUND_UNKNOWN	547	=item EIO_READDIR_FOUND_UNKNOWN
517		548
518	This flag should not be specified when calling C<eio_readdir>. Instead,	549	This flag should not be specified when calling C<eio_readdir>. Instead,
519	it is being set by C<eio_readdir> (you can access the C<flags> via C<<	550	it is being set by C<eio_readdir> (you can access the C<flags> via C<<
520	req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The	551	req->int1 >>, when any of the C<type>'s found were C<EIO_DT_UNKNOWN>. The
521	absense of this flag therefore indicates that all C<type>'s are known,	552	absence of this flag therefore indicates that all C<type>'s are known,
522	which can be used to speed up some algorithms.	553	which can be used to speed up some algorithms.
523		554
524	A typical use case would be to identify all subdirectories within a	555	A typical use case would be to identify all subdirectories within a
525	directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If	556	directory - you would ask C<eio_readdir> for C<EIO_READDIR_DIRS_FIRST>. If
526	then this flag is I<NOT> set, then all the entries at the beginning of the	557	then this flag is I<NOT> set, then all the entries at the beginning of the
…		…
556	=item eio_readahead (int fd, off_t offset, size_t length, int pri, eio_cb cb, void *data)	587	=item eio_readahead (int fd, off_t offset, size_t length, int pri, eio_cb cb, void *data)
557		588
558	Calls C<readahead(2)>. If the syscall is missing, then the call is	589	Calls C<readahead(2)>. If the syscall is missing, then the call is
559	emulated by simply reading the data (currently in 64kiB chunks).	590	emulated by simply reading the data (currently in 64kiB chunks).
560		591
		592	=item eio_syncfs (int fd, int pri, eio_cb cb, void *data)
		593
		594	Calls Linux' C<syncfs> syscall, if available. Returns C<-1> and sets
		595	C<errno> to C<ENOSYS> if the call is missing I<but still calls sync()>,
		596	if the C<fd> is C<< >= 0 >>, so you can probe for the availability of the
		597	syscall with a negative C<fd> argument and checking for C<-1/ENOSYS>.
		598
561	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)	599	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)
562		600
563	Calls C<sync_file_range>. If the syscall is missing, then this is the same	601	Calls C<sync_file_range>. If the syscall is missing, then this is the same
564	as calling C<fdatasync>.	602	as calling C<fdatasync>.
565		603
		604	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,
		605	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
		606
		607	=item eio_fallocate (int fd, int mode, off_t offset, off_t len, int pri, eio_cb cb, void *data)
		608
		609	Calls C<fallocate> (note: I<NOT> C<posix_fallocate>!). If the syscall is
		610	missing, then it returns failure and sets C<errno> to C<ENOSYS>.
		611
		612	The C<mode> argument can be C<0> (for behaviour similar to
		613	C<posix_fallocate>), or C<EIO_FALLOC_FL_KEEP_SIZE>, which keeps the size
		614	of the file unchanged (but still preallocates space beyond end of file).
		615
566	=back	616	=back
567		617
568	=head3 LIBEIO-SPECIFIC REQUESTS	618	=head3 LIBEIO-SPECIFIC REQUESTS
569		619
570	These requests are specific to libeio and do not correspond to any OS call.	620	These requests are specific to libeio and do not correspond to any OS call.
571		621
572	=over 4	622	=over 4
573		623
574	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)	624	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
575		625
		626	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY>) the given
		627	memory area, page-wise, that is, it reads (or reads and writes back) the
		628	first octet of every page that spans the memory area.
		629
		630	This can be used to page in some mmapped file, or dirty some pages. Note
		631	that dirtying is an unlocked read-write access, so races can ensue when
		632	the some other thread modifies the data stored in that memory area.
		633
576	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)	634	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)
577		635
578	Executes a custom request, i.e., a user-specified callback.	636	Executes a custom request, i.e., a user-specified callback.
579		637
580	The callback gets the C<eio_req *> as parameter and is expected to read	638	The callback gets the C<eio_req *> as parameter and is expected to read
581	and modify any request-specific members. Specifically, it should set C<<	639	and modify any request-specific members. Specifically, it should set C<<
…		…
601	req->result = open (req->data, O_RDONLY);	659	req->result = open (req->data, O_RDONLY);
602	}	660	}
603		661
604	eio_custom (my_open, 0, my_open_done, "/etc/passwd");	662	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
605		663
606	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)	664	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
607		665
608	This is a a request that takes C<delay> seconds to execute, but otherwise	666	This is a request that takes C<delay> seconds to execute, but otherwise
609	does nothing - it simply puts one of the worker threads to sleep for this	667	does nothing - it simply puts one of the worker threads to sleep for this
610	long.	668	long.
611		669
612	This request can be used to artificially increase load, e.g. for debugging	670	This request can be used to artificially increase load, e.g. for debugging
613	or benchmarking reasons.	671	or benchmarking reasons.
614		672
615	=item eio_nop (int pri, eio_cb cb, void *data)	673	=item eio_nop (int pri, eio_cb cb, void *data)
616		674
617	This request does nothing, except go through the whole request cycle. This	675	This request does nothing, except go through the whole request cycle. This
618	can be used to measure latency or in some cases to simplify code, but is	676	can be used to measure latency or in some cases to simplify code, but is
619	not really of much use.	677	not really of much use.
620		678
621	=back	679	=back
622		680
623	=head3 GROUPING AND LIMITING REQUESTS	681	=head3 GROUPING AND LIMITING REQUESTS
624		682
		683	There is one more rather special request, C<eio_grp>. It is a very special
		684	aio request: Instead of doing something, it is a container for other eio
		685	requests.
		686
		687	There are two primary use cases for this: a) bundle many requests into a
		688	single, composite, request with a definite callback and the ability to
		689	cancel the whole request with its subrequests and b) limiting the number
		690	of "active" requests.
		691
		692	Further below you will find more discussion of these topics - first
		693	follows the reference section detailing the request generator and other
		694	methods.
		695
		696	=over 4
		697
		698	=item eio_req grp = eio_grp (eio_cb cb, void data)
		699
		700	Creates, submits and returns a group request. Note that it doesn't have a
		701	priority, unlike all other requests.
		702
		703	=item eio_grp_add (eio_req grp, eio_req req)
		704
		705	Adds a request to the request group.
		706
		707	=item eio_grp_cancel (eio_req *grp)
		708
		709	Cancels all requests I<in> the group, but I<not> the group request
		710	itself. You can cancel the group request I<and> all subrequests via a
		711	normal C<eio_cancel> call.
		712
		713	=back
		714
		715	=head4 GROUP REQUEST LIFETIME
		716
		717	Left alone, a group request will instantly move to the pending state and
		718	will be finished at the next call of C<eio_poll>.
		719
		720	The usefulness stems from the fact that, if a subrequest is added to a
		721	group I<before> a call to C<eio_poll>, via C<eio_grp_add>, then the group
		722	will not finish until all the subrequests have finished.
		723
		724	So the usage cycle of a group request is like this: after it is created,
		725	you normally instantly add a subrequest. If none is added, the group
		726	request will finish on it's own. As long as subrequests are added before
		727	the group request is finished it will be kept from finishing, that is the
		728	callbacks of any subrequests can, in turn, add more requests to the group,
		729	and as long as any requests are active, the group request itself will not
		730	finish.
		731
		732	=head4 CREATING COMPOSITE REQUESTS
		733
		734	Imagine you wanted to create an C<eio_load> request that opens a file,
		735	reads it and closes it. This means it has to execute at least three eio
		736	requests, but for various reasons it might be nice if that request looked
		737	like any other eio request.
		738
		739	This can be done with groups:
		740
		741	=over 4
		742
		743	=item 1) create the request object
		744
		745	Create a group that contains all further requests. This is the request you
		746	can return as "the load request".
		747
		748	=item 2) open the file, maybe
		749
		750	Next, open the file with C<eio_open> and add the request to the group
		751	request and you are finished setting up the request.
		752
		753	If, for some reason, you cannot C<eio_open> (path is a null ptr?) you
		754	can set C<< grp->result >> to C<-1> to signal an error and let the group
		755	request finish on its own.
		756
		757	=item 3) open callback adds more requests
		758
		759	In the open callback, if the open was not successful, copy C<<
		760	req->errorno >> to C<< grp->errorno >> and set C<< grp->result >> to
		761	C<-1> to signal an error.
		762
		763	Otherwise, malloc some memory or so and issue a read request, adding the
		764	read request to the group.
		765
		766	=item 4) continue issuing requests till finished
		767
		768	In the read callback, check for errors and possibly continue with
		769	C<eio_close> or any other eio request in the same way.
		770
		771	As soon as no new requests are added, the group request will finish. Make
		772	sure you I<always> set C<< grp->result >> to some sensible value.
		773
		774	=back
		775
		776	=head4 REQUEST LIMITING
		777
		778
625	#TODO	779	#TODO
626		780
627	/*****************************************************************************/
628	/* groups */
629
630	eio_req eio_grp (eio_cb cb, void data);
631	void eio_grp_feed (eio_req grp, void (feed)(eio_req *req), int limit);
632	void eio_grp_limit (eio_req *grp, int limit);	781	void eio_grp_limit (eio_req *grp, int limit);
633	void eio_grp_add (eio_req grp, eio_req req);
634	void eio_grp_cancel (eio_req grp); / cancels all sub requests but not the group */
635		782
636
637	=back
638		783
639		784
640	=head1 LOW LEVEL REQUEST API	785	=head1 LOW LEVEL REQUEST API
641		786
642	#TODO	787	#TODO
…		…
645	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST	790	=head1 ANATOMY AND LIFETIME OF AN EIO REQUEST
646		791
647	A request is represented by a structure of type C<eio_req>. To initialise	792	A request is represented by a structure of type C<eio_req>. To initialise
648	it, clear it to all zero bytes:	793	it, clear it to all zero bytes:
649		794
650	eio_req req;	795	eio_req req;
651		796
652	memset (&req, 0, sizeof (req));	797	memset (&req, 0, sizeof (req));
653		798
654	A more common way to initialise a new C<eio_req> is to use C<calloc>:	799	A more common way to initialise a new C<eio_req> is to use C<calloc>:
655		800
656	eio_req req = calloc (1, sizeof (req));	801	eio_req req = calloc (1, sizeof (req));
657		802
658	In either case, libeio neither allocates, initialises or frees the	803	In either case, libeio neither allocates, initialises or frees the
659	C<eio_req> structure for you - it merely uses it.	804	C<eio_req> structure for you - it merely uses it.
660		805
661	zero	806	zero
662		807
663	#TODO	808	#TODO
		809
		810	=head2 CONFIGURATION
		811
		812	The functions in this section can sometimes be useful, but the default
		813	configuration will do in most case, so you should skip this section on
		814	first reading.
		815
		816	=over 4
		817
		818	=item eio_set_max_poll_time (eio_tstamp nseconds)
		819
		820	This causes C<eio_poll ()> to return after it has detected that it was
		821	running for C<nsecond> seconds or longer (this number can be fractional).
		822
		823	This can be used to limit the amount of time spent handling eio requests,
		824	for example, in interactive programs, you might want to limit this time to
		825	C<0.01> seconds or so.
		826
		827	Note that:
		828
		829	=over 4
		830
		831	=item a) libeio doesn't know how long your request callbacks take, so the
		832	time spent in C<eio_poll> is up to one callback invocation longer then
		833	this interval.
		834
		835	=item b) this is implemented by calling C<gettimeofday> after each
		836	request, which can be costly.
		837
		838	=item c) at least one request will be handled.
		839
		840	=back
		841
		842	=item eio_set_max_poll_reqs (unsigned int nreqs)
		843
		844	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than
		845	C<nreqs> requests per invocation. This is a less costly way to limit the
		846	amount of work done by C<eio_poll> then setting a time limit.
		847
		848	If you know your callbacks are generally fast, you could use this to
		849	encourage interactiveness in your programs by setting it to C<10>, C<100>
		850	or even C<1000>.
		851
		852	=item eio_set_min_parallel (unsigned int nthreads)
		853
		854	Make sure libeio can handle at least this many requests in parallel. It
		855	might be able handle more.
		856
		857	=item eio_set_max_parallel (unsigned int nthreads)
		858
		859	Set the maximum number of threads that libeio will spawn.
		860
		861	=item eio_set_max_idle (unsigned int nthreads)
		862
		863	Libeio uses threads internally to handle most requests, and will start and stop threads on demand.
		864
		865	This call can be used to limit the number of idle threads (threads without
		866	work to do): libeio will keep some threads idle in preparation for more
		867	requests, but never longer than C<nthreads> threads.
		868
		869	In addition to this, libeio will also stop threads when they are idle for
		870	a few seconds, regardless of this setting.
		871
		872	=item unsigned int eio_nthreads ()
		873
		874	Return the number of worker threads currently running.
		875
		876	=item unsigned int eio_nreqs ()
		877
		878	Return the number of requests currently handled by libeio. This is the
		879	total number of requests that have been submitted to libeio, but not yet
		880	destroyed.
		881
		882	=item unsigned int eio_nready ()
		883
		884	Returns the number of ready requests, i.e. requests that have been
		885	submitted but have not yet entered the execution phase.
		886
		887	=item unsigned int eio_npending ()
		888
		889	Returns the number of pending requests, i.e. requests that have been
		890	executed and have results, but have not been finished yet by a call to
		891	C<eio_poll>).
		892
		893	=back
664		894
665	=head1 EMBEDDING	895	=head1 EMBEDDING
666		896
667	Libeio can be embedded directly into programs. This functionality is not	897	Libeio can be embedded directly into programs. This functionality is not
668	documented and not (yet) officially supported.	898	documented and not (yet) officially supported.
…		…
685	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
686	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>
687	requests, you might want to increase this.	917	requests, you might want to increase this.
688		918
689	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
690	stack size (C<sizeof (long) * 4096> currently). If it is defined, but	920	stack size (C<sizeof (void ) 4096> currently). In all other cases, the
691	C<0>, then the default operating system stack size will be used. In all
692	other cases, the value must be an expression that evaluates to the desired	921	value must be an expression that evaluates to the desired stack size.
693	stack size.
694		922
695	=back	923	=back
696		924
697		925
698	=head1 PORTABILITY REQUIREMENTS	926	=head1 PORTABILITY REQUIREMENTS

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Revision 1.7 by root, Sun Jun 5 22:44:30 2011 UTC vs.
Revision 1.36 by root, Sun Jan 24 16:36:20 2016 UTC