[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 1.16 by root, Tue Jul 5 17:05:54 2011 UTC

…		…
124	=back	124	=back
125		125
126	For libev, you would typically use an C<ev_async> watcher: the	126	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	127	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	128	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	129	()>.
130	all requests have been handled yet). The race is taken care of because	130
131	libev resets/rearms the async watcher before calling your callback,	131	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)	132	(i.e. it returns C<-1>) then you should start an idle watcher that calls
133	spurious wake-ups, but is generally harmless.	133	C<eio_poll> until it returns something C<!= -1>.
		134
		135	A full-featured conenctor between libeio and libev would look as follows
		136	(if C<eio_poll> is handling all requests, it can of course be simplified a
		137	lot by removing the idle watcher logic):
		138
		139	static struct ev_loop *loop;
		140	static ev_idle repeat_watcher;
		141	static ev_async ready_watcher;
		142
		143	/* idle watcher callback, only used when eio_poll */
		144	/* didn't handle all results in one call */
		145	static void
		146	repeat (EV_P_ ev_idle *w, int revents)
		147	{
		148	if (eio_poll () != -1)
		149	ev_idle_stop (EV_A_ w);
		150	}
		151
		152	/* eio has some results, process them */
		153	static void
		154	ready (EV_P_ ev_async *w, int revents)
		155	{
		156	if (eio_poll () == -1)
		157	ev_idle_start (EV_A_ &repeat_watcher);
		158	}
		159
		160	/* wake up the event loop */
		161	static void
		162	want_poll (void)
		163	{
		164	ev_async_send (loop, &ready_watcher)
		165	}
		166
		167	void
		168	my_init_eio ()
		169	{
		170	loop = EV_DEFAULT;
		171
		172	ev_idle_init (&repeat_watcher, repeat);
		173	ev_async_init (&ready_watcher, ready);
		174	ev_async_start (loop &watcher);
		175
		176	eio_init (want_poll, 0);
		177	}
134		178
135	For most other event loops, you would typically use a pipe - the event	179	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	180	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	181	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	182	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>).	183	C<eio_poll>.
221		184
222	=back	185	You don't have to take special care in the case C<eio_poll> doesn't handle
		186	all requests, as the done callback will not be invoked, so the event loop
		187	will still signal readyness for the pipe until I<all> results have been
		188	processed.
223		189
224		190
225	=head1 HIGH LEVEL REQUEST API	191	=head1 HIGH LEVEL REQUEST API
226		192
227	Libeio has both a high-level API, which consists of calling a request	193	Libeio has both a high-level API, which consists of calling a request
…		…
234		200
235	You submit a request by calling the relevant C<eio_TYPE> function with the	201	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)>	202	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.	203	(called C<eio_cb> below) and a freely usable C<void *data> argument.
238		204
239	The return value will either be 0	205	The return value will either be 0, in case something went really wrong
		206	(which can basically only happen on very fatal errors, such as C<malloc>
		207	returning 0, which is rather unlikely), or a pointer to the newly-created
		208	and submitted C<eio_req *>.
240		209
241	The callback will be called with an C<eio_req *> which contains the	210	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	211	results of the request. The members you can access inside that structure
243	vary from request to request, except for:	212	vary from request to request, except for:
244		213
…		…
307	custom data value as C<data>.	276	custom data value as C<data>.
308		277
309	=head3 POSIX API WRAPPERS	278	=head3 POSIX API WRAPPERS
310		279
311	These requests simply wrap the POSIX call of the same name, with the same	280	These requests simply wrap the POSIX call of the same name, with the same
312	arguments:	281	arguments. If a function is not implemented by the OS and cannot be emulated
		282	in some way, then all of these return C<-1> and set C<errorno> to C<ENOSYS>.
313		283
314	=over 4	284	=over 4
315		285
316	=item eio_open (const char path, int flags, mode_t mode, int pri, eio_cb cb, void data)	286	=item eio_open (const char path, int flags, mode_t mode, int pri, eio_cb cb, void data)
317		287
		288	=item eio_truncate (const char path, off_t offset, int pri, eio_cb cb, void data)
		289
		290	=item eio_chown (const char path, uid_t uid, gid_t gid, int pri, eio_cb cb, void data)
		291
		292	=item eio_chmod (const char path, mode_t mode, int pri, eio_cb cb, void data)
		293
		294	=item eio_mkdir (const char path, mode_t mode, int pri, eio_cb cb, void data)
		295
		296	=item eio_rmdir (const char path, int pri, eio_cb cb, void data)
		297
		298	=item eio_unlink (const char path, int pri, eio_cb cb, void data)
		299
318	=item eio_utime (const char path, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void data)	300	=item eio_utime (const char path, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void data)
319		301
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)	302	=item eio_mknod (const char path, mode_t mode, dev_t dev, int pri, eio_cb cb, void data)
341		303
342	=item eio_link (const char path, const char new_path, int pri, eio_cb cb, void *data)	304	=item eio_link (const char path, const char new_path, int pri, eio_cb cb, void *data)
343		305
344	=item eio_symlink (const char path, const char new_path, int pri, eio_cb cb, void *data)	306	=item eio_symlink (const char path, const char new_path, int pri, eio_cb cb, void *data)
345		307
346	=item eio_rename (const char path, const char new_path, int pri, eio_cb cb, void *data)	308	=item eio_rename (const char path, const char new_path, int pri, eio_cb cb, void *data)
347		309
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)	310	=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		311
354	=item eio_close (int fd, int pri, eio_cb cb, void *data)	312	=item eio_close (int fd, int pri, eio_cb cb, void *data)
355		313
356	=item eio_sync (int pri, eio_cb cb, void *data)	314	=item eio_sync (int pri, eio_cb cb, void *data)
357		315
…		…
386		344
387	Not surprisingly, pread and pwrite are not thread-safe on Darwin (OS/X),	345	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	346	so it is advised not to submit multiple requests on the same fd on this
389	horrible pile of garbage.	347	horrible pile of garbage.
390		348
		349	=item eio_mlockall (int flags, int pri, eio_cb cb, void *data)
		350
		351	Like C<mlockall>, but the flag value constants are called
		352	C<EIO_MCL_CURRENT> and C<EIO_MCL_FUTURE>.
		353
		354	=item eio_msync (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
		355
		356	Just like msync, except that the flag values are called C<EIO_MS_ASYNC>,
		357	C<EIO_MS_INVALIDATE> and C<EIO_MS_SYNC>.
		358
		359	=item eio_readlink (const char path, int pri, eio_cb cb, void data)
		360
		361	If successful, the path read by C<readlink(2)> can be accessed via C<<
		362	req->ptr2 >> and is I<NOT> null-terminated, with the length specified as
		363	C<< req->result >>.
		364
		365	if (req->result >= 0)
		366	{
		367	char target = strndup ((char )req->ptr2, req->result);
		368
		369	free (target);
		370	}
		371
		372	=item eio_realpath (const char path, int pri, eio_cb cb, void data)
		373
		374	Similar to the realpath libc function, but unlike that one, result is
		375	C<-1> on failure and the length of the returned path in C<ptr2> (which is
		376	not 0-terminated) - this is similar to readlink.
		377
		378	=item eio_stat (const char path, int pri, eio_cb cb, void data)
		379
		380	=item eio_lstat (const char path, int pri, eio_cb cb, void data)
		381
391	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)	382	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)
392		383
393	Stats a file - if C<< req->result >> indicates success, then you can	384	Stats a file - if C<< req->result >> indicates success, then you can
394	access the C<struct stat>-like structure via C<< req->ptr2 >>:	385	access the C<struct stat>-like structure via C<< req->ptr2 >>:
395		386
396	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;	387	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
397		388
398	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void data) / stat buffer=ptr2 allocated dynamically */	389	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)
		390
		391	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)
399		392
400	Stats a filesystem - if C<< req->result >> indicates success, then you can	393	Stats a filesystem - if C<< req->result >> indicates success, then you can
401	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:	394	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
402		395
403	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;	396	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
…		…
419	(via the C<opendir>, C<readdir> and C<closedir> calls) and returns either	412	(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>	413	the names or an array of C<struct eio_dirent>, depending on the C<flags>
421	argument.	414	argument.
422		415
423	The C<< req->result >> indicates either the number of files found, or	416	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 >>,	417	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<<	418	and C<struct eio_dirents>, if requested by C<flags>, can be found via C<<
426	req->ptr1 >>.	419	req->ptr1 >>.
427		420
428	Here is an example that prints all the names:	421	Here is an example that prints all the names:
429		422
…		…
561	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)	554	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)
562		555
563	Calls C<sync_file_range>. If the syscall is missing, then this is the same	556	Calls C<sync_file_range>. If the syscall is missing, then this is the same
564	as calling C<fdatasync>.	557	as calling C<fdatasync>.
565		558
		559	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,
		560	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
		561
566	=back	562	=back
567		563
568	=head3 LIBEIO-SPECIFIC REQUESTS	564	=head3 LIBEIO-SPECIFIC REQUESTS
569		565
570	These requests are specific to libeio and do not correspond to any OS call.	566	These requests are specific to libeio and do not correspond to any OS call.
571		567
572	=over 4	568	=over 4
573		569
574	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)	570	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
575		571
		572	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY) the given
		573	memory area, page-wise, that is, it reads (or reads and writes back) the
		574	first octet of every page that spans the memory area.
		575
		576	This can be used to page in some mmapped file, or dirty some pages. Note
		577	that dirtying is an unlocked read-write access, so races can ensue when
		578	the some other thread modifies the data stored in that memory area.
		579
576	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)	580	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)
577		581
578	Executes a custom request, i.e., a user-specified callback.	582	Executes a custom request, i.e., a user-specified callback.
579		583
580	The callback gets the C<eio_req *> as parameter and is expected to read	584	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<<	585	and modify any request-specific members. Specifically, it should set C<<
…		…
601	req->result = open (req->data, O_RDONLY);	605	req->result = open (req->data, O_RDONLY);
602	}	606	}
603		607
604	eio_custom (my_open, 0, my_open_done, "/etc/passwd");	608	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
605		609
606	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)	610	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
607		611
608	This is a a request that takes C<delay> seconds to execute, but otherwise	612	This is a 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	613	does nothing - it simply puts one of the worker threads to sleep for this
610	long.	614	long.
611		615
612	This request can be used to artificially increase load, e.g. for debugging	616	This request can be used to artificially increase load, e.g. for debugging
613	or benchmarking reasons.	617	or benchmarking reasons.
614		618
615	=item eio_nop (int pri, eio_cb cb, void *data)	619	=item eio_nop (int pri, eio_cb cb, void *data)
616		620
617	This request does nothing, except go through the whole request cycle. This	621	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	622	can be used to measure latency or in some cases to simplify code, but is
619	not really of much use.	623	not really of much use.
620		624
621	=back	625	=back
622		626
623	=head3 GROUPING AND LIMITING REQUESTS	627	=head3 GROUPING AND LIMITING REQUESTS
		628
		629	There is one more rather special request, C<eio_grp>. It is a very special
		630	aio request: Instead of doing something, it is a container for other eio
		631	requests.
		632
		633	There are two primary use cases for this: a) bundle many requests into a
		634	single, composite, request with a definite callback and the ability to
		635	cancel the whole request with its subrequests and b) limiting the number
		636	of "active" requests.
		637
		638	Further below you will find more dicussion of these topics - first follows
		639	the reference section detailing the request generator and other methods.
		640
		641	=over 4
		642
		643	=item eio_grp (eio_cb cb, void *data)
		644
		645	Creates and submits a group request.
		646
		647	=back
		648
		649
624		650
625	#TODO	651	#TODO
626		652
627	/*****************************************************************************/	653	/*****************************************************************************/
628	/* groups */	654	/* groups */
…		…
660		686
661	zero	687	zero
662		688
663	#TODO	689	#TODO
664		690
		691	=head2 CONFIGURATION
		692
		693	The functions in this section can sometimes be useful, but the default
		694	configuration will do in most case, so you should skip this section on
		695	first reading.
		696
		697	=over 4
		698
		699	=item eio_set_max_poll_time (eio_tstamp nseconds)
		700
		701	This causes C<eio_poll ()> to return after it has detected that it was
		702	running for C<nsecond> seconds or longer (this number can be fractional).
		703
		704	This can be used to limit the amount of time spent handling eio requests,
		705	for example, in interactive programs, you might want to limit this time to
		706	C<0.01> seconds or so.
		707
		708	Note that:
		709
		710	a) libeio doesn't know how long your request callbacks take, so the time
		711	spent in C<eio_poll> is up to one callback invocation longer then this
		712	interval.
		713
		714	b) this is implemented by calling C<gettimeofday> after each request,
		715	which can be costly.
		716
		717	c) at least one request will be handled.
		718
		719	=item eio_set_max_poll_reqs (unsigned int nreqs)
		720
		721	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than
		722	C<nreqs> requests per invocation. This is a less costly way to limit the
		723	amount of work done by C<eio_poll> then setting a time limit.
		724
		725	If you know your callbacks are generally fast, you could use this to
		726	encourage interactiveness in your programs by setting it to C<10>, C<100>
		727	or even C<1000>.
		728
		729	=item eio_set_min_parallel (unsigned int nthreads)
		730
		731	Make sure libeio can handle at least this many requests in parallel. It
		732	might be able handle more.
		733
		734	=item eio_set_max_parallel (unsigned int nthreads)
		735
		736	Set the maximum number of threads that libeio will spawn.
		737
		738	=item eio_set_max_idle (unsigned int nthreads)
		739
		740	Libeio uses threads internally to handle most requests, and will start and stop threads on demand.
		741
		742	This call can be used to limit the number of idle threads (threads without
		743	work to do): libeio will keep some threads idle in preparation for more
		744	requests, but never longer than C<nthreads> threads.
		745
		746	In addition to this, libeio will also stop threads when they are idle for
		747	a few seconds, regardless of this setting.
		748
		749	=item unsigned int eio_nthreads ()
		750
		751	Return the number of worker threads currently running.
		752
		753	=item unsigned int eio_nreqs ()
		754
		755	Return the number of requests currently handled by libeio. This is the
		756	total number of requests that have been submitted to libeio, but not yet
		757	destroyed.
		758
		759	=item unsigned int eio_nready ()
		760
		761	Returns the number of ready requests, i.e. requests that have been
		762	submitted but have not yet entered the execution phase.
		763
		764	=item unsigned int eio_npending ()
		765
		766	Returns the number of pending requests, i.e. requests that have been
		767	executed and have results, but have not been finished yet by a call to
		768	C<eio_poll>).
		769
		770	=back
		771
665	=head1 EMBEDDING	772	=head1 EMBEDDING
666		773
667	Libeio can be embedded directly into programs. This functionality is not	774	Libeio can be embedded directly into programs. This functionality is not
668	documented and not (yet) officially supported.	775	documented and not (yet) officially supported.
669		776

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Comparing libeio/eio.pod (file contents): Revision 1.7 by root, Sun Jun 5 22:44:30 2011 UTC vs. Revision 1.16 by root, Tue Jul 5 17:05:54 2011 UTC

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Comparing libeio/eio.pod (file contents):
Revision 1.7 by root, Sun Jun 5 22:44:30 2011 UTC vs.
Revision 1.16 by root, Tue Jul 5 17:05:54 2011 UTC