[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 1.15 by root, Tue Jul 5 16:57:41 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 wrapper would look as follows (if C<eio_poll> is handling
		136	all requests, it can of course be simplified a lot by removing the idle
		137	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	183	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	184	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>).	185	read callback does not read it, only C<done_poll>).
142		186
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>).
221
222	=back
223
224		187
225	=head1 HIGH LEVEL REQUEST API	188	=head1 HIGH LEVEL REQUEST API
226		189
227	Libeio has both a high-level API, which consists of calling a request	190	Libeio has both a high-level API, which consists of calling a request
228	function with a callback to be called on completion, and a low-level API	191	function with a callback to be called on completion, and a low-level API
…		…
234		197
235	You submit a request by calling the relevant C<eio_TYPE> function with the	198	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)>	199	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.	200	(called C<eio_cb> below) and a freely usable C<void *data> argument.
238		201
239	The return value will either be 0	202	The return value will either be 0, in case something went really wrong
		203	(which can basically only happen on very fatal errors, such as C<malloc>
		204	returning 0, which is rather unlikely), or a pointer to the newly-created
		205	and submitted C<eio_req *>.
240		206
241	The callback will be called with an C<eio_req *> which contains the	207	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	208	results of the request. The members you can access inside that structure
243	vary from request to request, except for:	209	vary from request to request, except for:
244		210
…		…
307	custom data value as C<data>.	273	custom data value as C<data>.
308		274
309	=head3 POSIX API WRAPPERS	275	=head3 POSIX API WRAPPERS
310		276
311	These requests simply wrap the POSIX call of the same name, with the same	277	These requests simply wrap the POSIX call of the same name, with the same
312	arguments:	278	arguments. If a function is not implemented by the OS and cannot be emulated
		279	in some way, then all of these return C<-1> and set C<errorno> to C<ENOSYS>.
313		280
314	=over 4	281	=over 4
315		282
316	=item eio_open (const char path, int flags, mode_t mode, int pri, eio_cb cb, void data)	283	=item eio_open (const char path, int flags, mode_t mode, int pri, eio_cb cb, void data)
317		284
		285	=item eio_truncate (const char path, off_t offset, int pri, eio_cb cb, void data)
		286
		287	=item eio_chown (const char path, uid_t uid, gid_t gid, int pri, eio_cb cb, void data)
		288
		289	=item eio_chmod (const char path, mode_t mode, int pri, eio_cb cb, void data)
		290
		291	=item eio_mkdir (const char path, mode_t mode, int pri, eio_cb cb, void data)
		292
		293	=item eio_rmdir (const char path, int pri, eio_cb cb, void data)
		294
		295	=item eio_unlink (const char path, int pri, eio_cb cb, void data)
		296
318	=item eio_utime (const char path, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void data)	297	=item eio_utime (const char path, eio_tstamp atime, eio_tstamp mtime, int pri, eio_cb cb, void data)
319		298
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)	299	=item eio_mknod (const char path, mode_t mode, dev_t dev, int pri, eio_cb cb, void data)
341		300
342	=item eio_link (const char path, const char new_path, int pri, eio_cb cb, void *data)	301	=item eio_link (const char path, const char new_path, int pri, eio_cb cb, void *data)
343		302
344	=item eio_symlink (const char path, const char new_path, int pri, eio_cb cb, void *data)	303	=item eio_symlink (const char path, const char new_path, int pri, eio_cb cb, void *data)
345		304
346	=item eio_rename (const char path, const char new_path, int pri, eio_cb cb, void *data)	305	=item eio_rename (const char path, const char new_path, int pri, eio_cb cb, void *data)
347		306
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)	307	=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		308
354	=item eio_close (int fd, int pri, eio_cb cb, void *data)	309	=item eio_close (int fd, int pri, eio_cb cb, void *data)
355		310
356	=item eio_sync (int pri, eio_cb cb, void *data)	311	=item eio_sync (int pri, eio_cb cb, void *data)
357		312
…		…
386		341
387	Not surprisingly, pread and pwrite are not thread-safe on Darwin (OS/X),	342	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	343	so it is advised not to submit multiple requests on the same fd on this
389	horrible pile of garbage.	344	horrible pile of garbage.
390		345
		346	=item eio_mlockall (int flags, int pri, eio_cb cb, void *data)
		347
		348	Like C<mlockall>, but the flag value constants are called
		349	C<EIO_MCL_CURRENT> and C<EIO_MCL_FUTURE>.
		350
		351	=item eio_msync (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
		352
		353	Just like msync, except that the flag values are called C<EIO_MS_ASYNC>,
		354	C<EIO_MS_INVALIDATE> and C<EIO_MS_SYNC>.
		355
		356	=item eio_readlink (const char path, int pri, eio_cb cb, void data)
		357
		358	If successful, the path read by C<readlink(2)> can be accessed via C<<
		359	req->ptr2 >> and is I<NOT> null-terminated, with the length specified as
		360	C<< req->result >>.
		361
		362	if (req->result >= 0)
		363	{
		364	char target = strndup ((char )req->ptr2, req->result);
		365
		366	free (target);
		367	}
		368
		369	=item eio_realpath (const char path, int pri, eio_cb cb, void data)
		370
		371	Similar to the realpath libc function, but unlike that one, result is
		372	C<-1> on failure and the length of the returned path in C<ptr2> (which is
		373	not 0-terminated) - this is similar to readlink.
		374
		375	=item eio_stat (const char path, int pri, eio_cb cb, void data)
		376
		377	=item eio_lstat (const char path, int pri, eio_cb cb, void data)
		378
391	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)	379	=item eio_fstat (int fd, int pri, eio_cb cb, void *data)
392		380
393	Stats a file - if C<< req->result >> indicates success, then you can	381	Stats a file - if C<< req->result >> indicates success, then you can
394	access the C<struct stat>-like structure via C<< req->ptr2 >>:	382	access the C<struct stat>-like structure via C<< req->ptr2 >>:
395		383
396	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;	384	EIO_STRUCT_STAT statdata = (EIO_STRUCT_STAT )req->ptr2;
397		385
398	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void data) / stat buffer=ptr2 allocated dynamically */	386	=item eio_statvfs (const char path, int pri, eio_cb cb, void data)
		387
		388	=item eio_fstatvfs (int fd, int pri, eio_cb cb, void *data)
399		389
400	Stats a filesystem - if C<< req->result >> indicates success, then you can	390	Stats a filesystem - if C<< req->result >> indicates success, then you can
401	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:	391	access the C<struct statvfs>-like structure via C<< req->ptr2 >>:
402		392
403	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;	393	EIO_STRUCT_STATVFS statdata = (EIO_STRUCT_STATVFS )req->ptr2;
…		…
419	(via the C<opendir>, C<readdir> and C<closedir> calls) and returns either	409	(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>	410	the names or an array of C<struct eio_dirent>, depending on the C<flags>
421	argument.	411	argument.
422		412
423	The C<< req->result >> indicates either the number of files found, or	413	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 >>,	414	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<<	415	and C<struct eio_dirents>, if requested by C<flags>, can be found via C<<
426	req->ptr1 >>.	416	req->ptr1 >>.
427		417
428	Here is an example that prints all the names:	418	Here is an example that prints all the names:
429		419
…		…
561	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)	551	=item eio_sync_file_range (int fd, off_t offset, size_t nbytes, unsigned int flags, int pri, eio_cb cb, void *data)
562		552
563	Calls C<sync_file_range>. If the syscall is missing, then this is the same	553	Calls C<sync_file_range>. If the syscall is missing, then this is the same
564	as calling C<fdatasync>.	554	as calling C<fdatasync>.
565		555
		556	Flags can be any combination of C<EIO_SYNC_FILE_RANGE_WAIT_BEFORE>,
		557	C<EIO_SYNC_FILE_RANGE_WRITE> and C<EIO_SYNC_FILE_RANGE_WAIT_AFTER>.
		558
566	=back	559	=back
567		560
568	=head3 LIBEIO-SPECIFIC REQUESTS	561	=head3 LIBEIO-SPECIFIC REQUESTS
569		562
570	These requests are specific to libeio and do not correspond to any OS call.	563	These requests are specific to libeio and do not correspond to any OS call.
571		564
572	=over 4	565	=over 4
573		566
574	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)	567	=item eio_mtouch (void addr, size_t length, int flags, int pri, eio_cb cb, void data)
575		568
		569	Reads (C<flags == 0>) or modifies (C<flags == EIO_MT_MODIFY) the given
		570	memory area, page-wise, that is, it reads (or reads and writes back) the
		571	first octet of every page that spans the memory area.
		572
		573	This can be used to page in some mmapped file, or dirty some pages. Note
		574	that dirtying is an unlocked read-write access, so races can ensue when
		575	the some other thread modifies the data stored in that memory area.
		576
576	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)	577	=item eio_custom (void ()(eio_req ) execute, int pri, eio_cb cb, void *data)
577		578
578	Executes a custom request, i.e., a user-specified callback.	579	Executes a custom request, i.e., a user-specified callback.
579		580
580	The callback gets the C<eio_req *> as parameter and is expected to read	581	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<<	582	and modify any request-specific members. Specifically, it should set C<<
…		…
601	req->result = open (req->data, O_RDONLY);	602	req->result = open (req->data, O_RDONLY);
602	}	603	}
603		604
604	eio_custom (my_open, 0, my_open_done, "/etc/passwd");	605	eio_custom (my_open, 0, my_open_done, "/etc/passwd");
605		606
606	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)	607	=item eio_busy (eio_tstamp delay, int pri, eio_cb cb, void *data)
607		608
608	This is a a request that takes C<delay> seconds to execute, but otherwise	609	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	610	does nothing - it simply puts one of the worker threads to sleep for this
610	long.	611	long.
611		612
612	This request can be used to artificially increase load, e.g. for debugging	613	This request can be used to artificially increase load, e.g. for debugging
613	or benchmarking reasons.	614	or benchmarking reasons.
614		615
615	=item eio_nop (int pri, eio_cb cb, void *data)	616	=item eio_nop (int pri, eio_cb cb, void *data)
616		617
617	This request does nothing, except go through the whole request cycle. This	618	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	619	can be used to measure latency or in some cases to simplify code, but is
619	not really of much use.	620	not really of much use.
620		621
621	=back	622	=back
622		623
623	=head3 GROUPING AND LIMITING REQUESTS	624	=head3 GROUPING AND LIMITING REQUESTS
		625
		626	There is one more rather special request, C<eio_grp>. It is a very special
		627	aio request: Instead of doing something, it is a container for other eio
		628	requests.
		629
		630	There are two primary use cases for this: a) bundle many requests into a
		631	single, composite, request with a definite callback and the ability to
		632	cancel the whole request with its subrequests and b) limiting the number
		633	of "active" requests.
		634
		635	Further below you will find more dicussion of these topics - first follows
		636	the reference section detailing the request generator and other methods.
		637
		638	=over 4
		639
		640	=item eio_grp (eio_cb cb, void *data)
		641
		642	Creates and submits a group request.
		643
		644	=back
		645
		646
624		647
625	#TODO	648	#TODO
626		649
627	/*****************************************************************************/	650	/*****************************************************************************/
628	/* groups */	651	/* groups */
…		…
660		683
661	zero	684	zero
662		685
663	#TODO	686	#TODO
664		687
		688	=head2 CONFIGURATION
		689
		690	The functions in this section can sometimes be useful, but the default
		691	configuration will do in most case, so you should skip this section on
		692	first reading.
		693
		694	=over 4
		695
		696	=item eio_set_max_poll_time (eio_tstamp nseconds)
		697
		698	This causes C<eio_poll ()> to return after it has detected that it was
		699	running for C<nsecond> seconds or longer (this number can be fractional).
		700
		701	This can be used to limit the amount of time spent handling eio requests,
		702	for example, in interactive programs, you might want to limit this time to
		703	C<0.01> seconds or so.
		704
		705	Note that:
		706
		707	a) libeio doesn't know how long your request callbacks take, so the time
		708	spent in C<eio_poll> is up to one callback invocation longer then this
		709	interval.
		710
		711	b) this is implemented by calling C<gettimeofday> after each request,
		712	which can be costly.
		713
		714	c) at least one request will be handled.
		715
		716	=item eio_set_max_poll_reqs (unsigned int nreqs)
		717
		718	When C<nreqs> is non-zero, then C<eio_poll> will not handle more than
		719	C<nreqs> requests per invocation. This is a less costly way to limit the
		720	amount of work done by C<eio_poll> then setting a time limit.
		721
		722	If you know your callbacks are generally fast, you could use this to
		723	encourage interactiveness in your programs by setting it to C<10>, C<100>
		724	or even C<1000>.
		725
		726	=item eio_set_min_parallel (unsigned int nthreads)
		727
		728	Make sure libeio can handle at least this many requests in parallel. It
		729	might be able handle more.
		730
		731	=item eio_set_max_parallel (unsigned int nthreads)
		732
		733	Set the maximum number of threads that libeio will spawn.
		734
		735	=item eio_set_max_idle (unsigned int nthreads)
		736
		737	Libeio uses threads internally to handle most requests, and will start and stop threads on demand.
		738
		739	This call can be used to limit the number of idle threads (threads without
		740	work to do): libeio will keep some threads idle in preparation for more
		741	requests, but never longer than C<nthreads> threads.
		742
		743	In addition to this, libeio will also stop threads when they are idle for
		744	a few seconds, regardless of this setting.
		745
		746	=item unsigned int eio_nthreads ()
		747
		748	Return the number of worker threads currently running.
		749
		750	=item unsigned int eio_nreqs ()
		751
		752	Return the number of requests currently handled by libeio. This is the
		753	total number of requests that have been submitted to libeio, but not yet
		754	destroyed.
		755
		756	=item unsigned int eio_nready ()
		757
		758	Returns the number of ready requests, i.e. requests that have been
		759	submitted but have not yet entered the execution phase.
		760
		761	=item unsigned int eio_npending ()
		762
		763	Returns the number of pending requests, i.e. requests that have been
		764	executed and have results, but have not been finished yet by a call to
		765	C<eio_poll>).
		766
		767	=back
		768
665	=head1 EMBEDDING	769	=head1 EMBEDDING
666		770
667	Libeio can be embedded directly into programs. This functionality is not	771	Libeio can be embedded directly into programs. This functionality is not
668	documented and not (yet) officially supported.	772	documented and not (yet) officially supported.
669		773

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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 1.15 by root, Tue Jul 5 16:57:41 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 1.15 by root, Tue Jul 5 16:57:41 2011 UTC