[ViewVC] Contents of: cvs/IO-AIO/Changes

Revision history for IO::AIO

TODO: better autoconf.pm that can return LIBS etc.
TODO: aio_cptree/mvtree
TODO: reduce condvar fairness: schedule hot-cache-threads first?
TODO: splice/tee/vmsplice/sync_file_range? (http://kerneltrap.org/node/6505 http://lwn.net/Articles/178199/)
TODO: aio_fcntl, at least for file-locking

        - fix a memory leak on aio_readlink.
        - bring back working fchmod.
        - nop and busy now set result to 0.
        - set errno to ENOMEM when allocation fails.

3.01 Sun May 11 03:07:03 CEST 2008
        - (libeio) make it compile on systems without readahead or readdir_r.
        - (libeio) improve configure check for readahead availability.
        - do not try to link against -lrt.
        - use a separate configure script for IO::AIO (not the libeio one).

3.0  Sun May 11 00:57:14 CEST 2008
        - added bin/treescan to the distribution.
        - switched to using libeio.
        - LOTS OF INCOMPATIBLE CHANGES:
          - remove signal functionality, it is not worth the effort.
          - max_outstanding no longer returns the previous number of requests.
          - poll_cb no longer returns number of requests.

2.62 Sat Apr 26 13:59:33 CEST 2008
        - port to solaris perls configured for old posix
          (analysed by Jost Krieger).
        - keep a reference to the perl filehandle object in aio_close,
          so it doesn't get closed prematurely, leading to ugly races.

2.61 Wed Apr 16 18:45:02 CEST 2008
        - fix treescan output duplication and improve output ordering.
          also display files given on the commandline.
        - use a different algorithm for aio_close that is faster
          and probably has even lower chances of blocking.
        - do our own stack memory management for threads - linux
          allocates outrageous amounts of VM (not so bad unless you
          use mlockall...), which severely limits the number of threads
          on 32-bit arches: stack size is the larger of PTHREAD_STACK_MIN
          and 4096 * sizeof (long) (usually this is 16..64k).

2.6  Sun Mar 30 08:28:11 CEST 2008
        - added aio_sync.
        - added aio_pathsync.
        - fix prototypes of (void) functions.

2.51 Sat Oct  6 16:04:54 CEST 2007
        - perlio isn't generally threadsafe, so aio_close could not work reliably.
          aio_close now tries a safe hack that might not be that asynchronous
          (see the manpage for details).
        - discard callback return values as to not grow the stack endlessly
          when poll_cb handles many requests without returning.
        - minor code cleanups.

2.5  Thu Oct  4 14:49:08 CEST 2007
        - replaced _fd2fh with faster xs code.
        - aio_close will now try to do "the right thing" and thus might
          work sensibly for the very first time.

2.41 Mon Sep 24 21:28:21 CEST 2007
        - after fork, invest some work to make sure that the poll_fileno
          stays stable (by dup2'ing the new fd over the old one), to make
          it easier for programs/libs that don't control their forking
          behaviour and cannot recreate their watchers.

2.4  Sun Aug  5 18:44:22 CEST 2007
        - add aio_truncate, aio_chmod, aio_chown, aio_utime (linux
          successfully demonstrated that you can block on futimes...).
        - allow undef as fileoffset for aio_read/write and use read/write(2)
          internally (useful for sockets or O_APPEND handles).
        - allow undef for length in aio_write.
        - negative dataoffsets work as expected now in aio_read/aio_write.
        - use NV instead of UV for 32 bit perls and file offsets, as NVs
          have a larger range then.
        - shared code between BDB and IO::AIO.
        - aio_busy was completely broken. now fixed.
        - readahead emulation now returns something.
        - correctly set errno to ENOSYS on unimplemented functions
          (should never happen, though).
        - large changes to make it partially compile and run on win32,
          but win32 lacks too much functionality, and perl overrides way
          too many functions with crashing versions.

2.33 Tue Jan 23 23:55:41 CET 2007
        - fix install path (Andreas J. Koenig).

2.32 Mon Jan 22 16:56:23 CET 2007
        - added aio_rmtree.
        - wow, aio_mkdir was missing.
        - aio_load did return undef on error, not -1.
        - use prefixexp not prefix in autoconf.pm
          (suggested by ... rt.cpan.org unreachable).
        - avoid installing autoconf.pm.

2.31 Sat Jan  6 03:46:02 CET 2007
        - added aio_load.

2.3  Sat Dec 23 05:48:07 CET 2006
        - fix off-by-one bug in aio_read, causing memory corruption
          or crashes.

2.21  Fri Dec 22 05:03:38 CET 2006
        - minor doc updates.
        - minor cleanups.
        - IO::AIO::poll returns request count.
        - undocumented and unfinished async-signal-reporting.

2.2  Tue Oct 31 00:31:00 CET 2006
        - minor doc updates.
        - added aio_readlink.
        - properly zero-terminate aio_read buffer.
        - fix aio_read/write with nonzero dataoffset.
        - reduced size of aio request structure.
        - better diagnostics when pathnames etc. are not byte-encoded;
          do not leak request in that case, either.

2.1  Sun Oct 29 02:01:57 CET 2006
        - INCOMPATIBLE CHANGE: replace IO::AIO::poll_some by
          IO::AIO::max_poll_reqs and IO::AIO::max_poll_time.
        - fix a bug in aio_move where it would fail everytime
          it would have to copy files manually.
        - doc updates.
        - start threads only on (very low) demand.
        - end superfluous threads automatically after 10s idling.
        - add IO::AIO::max_idle to control this.
        - some tuning applied to random places.
        - add aio_mknod.

2.0  Thu Oct 26 18:27:58 CEST 2006
        - minor incompatibility: max_outstanding semantics have changed.
        - major rewrite, consider all functionality EXPERIMENTAL.
        - aio requests can be cancelled.
        - callbacks can be (re-)set later.
        - aio requests can choose between 9 priorities.
        - add aio_group: aio requests can be grouped
          into composite requests.
        - generator interface for groups.
        - add IO::AIO::poll_some.
        - major documentation improvements.
        - very minor bugfixes.
        - add aio_nop for dummy requests.
        - add aio_busy mainly for benchmarking and debugging.
        - use "fast" mutexes on linux.
        - use dynamic (and larger) buffers instead of
          putting them onto the stack.
        - optimise x86 and amd64 a bit.
        - better error checking when ENOMEM.
        - hopefully fix mem and dirp leaks on fork.
        - warn about broken perl malloc.
        - compiles on cygwin (but pread is broken on cygwin
          which is not detected by autoconf, so you have to
          edit autoconf/config.h yourself to enable emulation).

1.8  Sat Jun 24 22:20:44 CEST 2006
        - add and/or document aio_rename, aio_link, aio_symlink and aio_move.

1.73 Wed Mar  1 22:49:32 CET 2006
        - codename "jost"
        - AIX/Solaris(?) aren't being helpful again, hardcode a value
          for NAME_MAX and drive with your eyes closed (reported by
          wcooley@nakedape.cc).

1.72 Thu Feb  2 00:40:44 CET 2006
        - another minor bug in aio_scandir, again, the callback was called
          twice when the directory can't be stat'ed.

1.71 Mon Dec 26 20:20:03 CET 2005
        - grr, another minor bug in aio_scandir, this time resulting
          in a runtime error.

1.7  Mon Dec 26 19:29:48 CET 2005
        - aio_scandir errornously called callback twice in some cases.
        - added AnyEvent example.

1.61 Wed Sep  7 19:40:42 CEST 2005
        - no longer include $Config{libs}, as distros include too much
          garbage in there that is not installed on typical systems
          (for example, debian links perl against -lgdbm and many more
          libraries despite perl not needing it, slowing down startup and
          wasting memory).

1.6  Tue Aug 30 17:44:44 CEST 2005
        - added aio_readdir, aio_scandir.
        - added aio_sendfile, including sendfile emulation when sendfile
          isn't available. Linux, FreeBSD and HP-UX might work (sendfilev
          support is unavailable on my solaris 8 machine, but preliminary
          code is there. What's lacking is configury stuff and testing...).

1.5  Sat Aug 20 02:32:19 CEST 2005
        - create the aio threads on demand only (good after forking).
        - somebody nagged about C89 compatibility, so this release should
          be C89 compatible, but no guarantees for future ones.
        - abort when the configure script fails.

1.4  Wed Aug 17 08:07:27 CEST 2005
        - forgot to recreate the pipe after forking, this could cause
          deadlocks.

1.3  Wed Aug 17 07:25:54 CEST 2005
        - properly propagate exceptions from callbacks, instead of silently
          eating them.
        - use a different fork algorithm that avoids recursive callback
          invocations and reduces fork latency in busy processes.
        - fix a bug where the buffer scalar in aio_read got assigned the wrong
          length after reading.
        - fix a bug where the child would process some outstanding requests
          from the parent.
        - make a copy of the callback scalar, to avoid some very uncommon
          (but valid) usages where the callback scalar changes.
        - the callback was never freed in aio_read/aio_write.
        - aio_read/aio_write will now set the readonly flag on the data
          scalar for better error reporting.

1.2  Wed Aug 17 01:22:58 CEST 2005
        - verified on cygwin, linux/amd64+ia32+alpha, solaris.
        - use SvPVbyte for filenames now. You *need* to encode your strings to
          the external filename encoding first.
        - fix the bug where filehandles could leak (again).
        - clarify freebsd situation: make it work and tell me how, or go away
          with your underdocumented, broken and outdated OS.
        - fork'ing should now be officially supported (where linux and
          posix contradict each other, I followed posix).
        - only call read() once per poll, not twice (speedup).
        - new functions: aio_rmdir, aio_symlink.
        - force callback arguments to be undef or a reference, for better
          error catching.

1.1  Sun Aug  7 05:27:23 CEST 2005
        - added configure script to detect availability of some calls.
          (imperfect, as we cannot detect things like -lrt due to missing
          feedback yet).
        - emulate fdatasync via fsync, pread/pwrite via unsafe read/write
          and readahead via manual reading on platforms lacking those.
        - ported t/03_errors.t+framework by Brad Fitzpatrick
          from Linux::AIO.
        - removed XOPEN_SOURCE because stupid solaris 9 doesn't
          compile with it enabled. Probably breaks others. Oh well.
        - try to be more careful with errno on non-threaded perls.
        - cygwins perl insisted on a matching open mode when morphing
          the fd to an fh.
        - convert sv's to "byte" encoding in aio_read/aio_write. Might
          do that for pathnames, too, in the future, so make sure you
          properly encode your pathnames.

1.0  Fri Jul 22 10:43:30 CEST 2005
        - aio_open did not reliably deliver (open) filehandles.
        - all aio_*-functions keep a reference to the filehandle so
          it doesn't go away while the aio requests is working on it.
        - disable warnings in AIO.pm.

0.9  Wed Jul 20 23:55:04 CEST 2005
        - allow recursive calls to poll_cb, use less locking calls, too.
        - fix the Gtk2-example in the SYNOPSIS.
        - use pread/pwrite not pread64/pwrite64. this was simply a leftover
          from Linux::AIO.
          (found by compiling on cygwin. Unfortunately, cygwin declares but
          does not implement pread/pwrite).
        - only include <sys/syscall.h> on linux.

0.5  Tue Jul 12 13:03:09 CEST 2005
        - removed #include <endian.h>, it's not portable, and we don't
          need it anyway.
        - link against -lrt, as it might contain goodies such as fdatasync,
          and often aio_read, which we do not use yet, but it shouldn't hurt.

0.4  Mon Jul 11 05:28:25 CEST 2005
        - added IO::AIO::flush, IO::AIO::poll.
        - make callback argument optional for all calls.

0.3  Mon Jul 11 01:42:37 CEST 2005
        - restructured manpage.
        - added SYNOPSIS with examples for Event, Glib, Tk.
        - remove explicit context support so I don't have to maintain
          it for threaded perls (i.e. it should work now :).

0.2  Sun Jul 10 22:57:12 CEST 2005
        - return immediately from poll_wait if nreqs==0.
        - get rid of the request pipe and use faster thread-thread
          communications for most requests and responses.

0.1
        - cloned from Linux::AIO, which is very similar.

Revision:	1.151
Committed:	Mon May 12 00:31:43 2008 UTC (16 years ago) by root
Branch:	MAIN
Changes since 1.150:	+2 -0 lines
Log Message:	* empty log message *
#	Content
1	Revision history for IO::AIO
2
3	TODO: better autoconf.pm that can return LIBS etc.
4	TODO: aio_cptree/mvtree
5	TODO: reduce condvar fairness: schedule hot-cache-threads first?
6	TODO: splice/tee/vmsplice/sync_file_range? (http://kerneltrap.org/node/6505 http://lwn.net/Articles/178199/)
7	TODO: aio_fcntl, at least for file-locking
8
9	- fix a memory leak on aio_readlink.
10	- bring back working fchmod.
11	- nop and busy now set result to 0.
12	- set errno to ENOMEM when allocation fails.
13
14	3.01 Sun May 11 03:07:03 CEST 2008
15	- (libeio) make it compile on systems without readahead or readdir_r.
16	- (libeio) improve configure check for readahead availability.
17	- do not try to link against -lrt.
18	- use a separate configure script for IO::AIO (not the libeio one).
19
20	3.0 Sun May 11 00:57:14 CEST 2008
21	- added bin/treescan to the distribution.
22	- switched to using libeio.
23	- LOTS OF INCOMPATIBLE CHANGES:
24	- remove signal functionality, it is not worth the effort.
25	- max_outstanding no longer returns the previous number of requests.
26	- poll_cb no longer returns number of requests.
27
28	2.62 Sat Apr 26 13:59:33 CEST 2008
29	- port to solaris perls configured for old posix
30	(analysed by Jost Krieger).
31	- keep a reference to the perl filehandle object in aio_close,
32	so it doesn't get closed prematurely, leading to ugly races.
33
34	2.61 Wed Apr 16 18:45:02 CEST 2008
35	- fix treescan output duplication and improve output ordering.
36	also display files given on the commandline.
37	- use a different algorithm for aio_close that is faster
38	and probably has even lower chances of blocking.
39	- do our own stack memory management for threads - linux
40	allocates outrageous amounts of VM (not so bad unless you
41	use mlockall...), which severely limits the number of threads
42	on 32-bit arches: stack size is the larger of PTHREAD_STACK_MIN
43	and 4096 * sizeof (long) (usually this is 16..64k).
44
45	2.6 Sun Mar 30 08:28:11 CEST 2008
46	- added aio_sync.
47	- added aio_pathsync.
48	- fix prototypes of (void) functions.
49
50	2.51 Sat Oct 6 16:04:54 CEST 2007
51	- perlio isn't generally threadsafe, so aio_close could not work reliably.
52	aio_close now tries a safe hack that might not be that asynchronous
53	(see the manpage for details).
54	- discard callback return values as to not grow the stack endlessly
55	when poll_cb handles many requests without returning.
56	- minor code cleanups.
57
58	2.5 Thu Oct 4 14:49:08 CEST 2007
59	- replaced _fd2fh with faster xs code.
60	- aio_close will now try to do "the right thing" and thus might
61	work sensibly for the very first time.
62
63	2.41 Mon Sep 24 21:28:21 CEST 2007
64	- after fork, invest some work to make sure that the poll_fileno
65	stays stable (by dup2'ing the new fd over the old one), to make
66	it easier for programs/libs that don't control their forking
67	behaviour and cannot recreate their watchers.
68
69	2.4 Sun Aug 5 18:44:22 CEST 2007
70	- add aio_truncate, aio_chmod, aio_chown, aio_utime (linux
71	successfully demonstrated that you can block on futimes...).
72	- allow undef as fileoffset for aio_read/write and use read/write(2)
73	internally (useful for sockets or O_APPEND handles).
74	- allow undef for length in aio_write.
75	- negative dataoffsets work as expected now in aio_read/aio_write.
76	- use NV instead of UV for 32 bit perls and file offsets, as NVs
77	have a larger range then.
78	- shared code between BDB and IO::AIO.
79	- aio_busy was completely broken. now fixed.
80	- readahead emulation now returns something.
81	- correctly set errno to ENOSYS on unimplemented functions
82	(should never happen, though).
83	- large changes to make it partially compile and run on win32,
84	but win32 lacks too much functionality, and perl overrides way
85	too many functions with crashing versions.
86
87	2.33 Tue Jan 23 23:55:41 CET 2007
88	- fix install path (Andreas J. Koenig).
89
90	2.32 Mon Jan 22 16:56:23 CET 2007
91	- added aio_rmtree.
92	- wow, aio_mkdir was missing.
93	- aio_load did return undef on error, not -1.
94	- use prefixexp not prefix in autoconf.pm
95	(suggested by ... rt.cpan.org unreachable).
96	- avoid installing autoconf.pm.
97
98	2.31 Sat Jan 6 03:46:02 CET 2007
99	- added aio_load.
100
101	2.3 Sat Dec 23 05:48:07 CET 2006
102	- fix off-by-one bug in aio_read, causing memory corruption
103	or crashes.
104
105	2.21 Fri Dec 22 05:03:38 CET 2006
106	- minor doc updates.
107	- minor cleanups.
108	- IO::AIO::poll returns request count.
109	- undocumented and unfinished async-signal-reporting.
110
111	2.2 Tue Oct 31 00:31:00 CET 2006
112	- minor doc updates.
113	- added aio_readlink.
114	- properly zero-terminate aio_read buffer.
115	- fix aio_read/write with nonzero dataoffset.
116	- reduced size of aio request structure.
117	- better diagnostics when pathnames etc. are not byte-encoded;
118	do not leak request in that case, either.
119
120	2.1 Sun Oct 29 02:01:57 CET 2006
121	- INCOMPATIBLE CHANGE: replace IO::AIO::poll_some by
122	IO::AIO::max_poll_reqs and IO::AIO::max_poll_time.
123	- fix a bug in aio_move where it would fail everytime
124	it would have to copy files manually.
125	- doc updates.
126	- start threads only on (very low) demand.
127	- end superfluous threads automatically after 10s idling.
128	- add IO::AIO::max_idle to control this.
129	- some tuning applied to random places.
130	- add aio_mknod.
131
132	2.0 Thu Oct 26 18:27:58 CEST 2006
133	- minor incompatibility: max_outstanding semantics have changed.
134	- major rewrite, consider all functionality EXPERIMENTAL.
135	- aio requests can be cancelled.
136	- callbacks can be (re-)set later.
137	- aio requests can choose between 9 priorities.
138	- add aio_group: aio requests can be grouped
139	into composite requests.
140	- generator interface for groups.
141	- add IO::AIO::poll_some.
142	- major documentation improvements.
143	- very minor bugfixes.
144	- add aio_nop for dummy requests.
145	- add aio_busy mainly for benchmarking and debugging.
146	- use "fast" mutexes on linux.
147	- use dynamic (and larger) buffers instead of
148	putting them onto the stack.
149	- optimise x86 and amd64 a bit.
150	- better error checking when ENOMEM.
151	- hopefully fix mem and dirp leaks on fork.
152	- warn about broken perl malloc.
153	- compiles on cygwin (but pread is broken on cygwin
154	which is not detected by autoconf, so you have to
155	edit autoconf/config.h yourself to enable emulation).
156
157	1.8 Sat Jun 24 22:20:44 CEST 2006
158	- add and/or document aio_rename, aio_link, aio_symlink and aio_move.
159
160	1.73 Wed Mar 1 22:49:32 CET 2006
161	- codename "jost"
162	- AIX/Solaris(?) aren't being helpful again, hardcode a value
163	for NAME_MAX and drive with your eyes closed (reported by
164	wcooley@nakedape.cc).
165
166	1.72 Thu Feb 2 00:40:44 CET 2006
167	- another minor bug in aio_scandir, again, the callback was called
168	twice when the directory can't be stat'ed.
169
170	1.71 Mon Dec 26 20:20:03 CET 2005
171	- grr, another minor bug in aio_scandir, this time resulting
172	in a runtime error.
173
174	1.7 Mon Dec 26 19:29:48 CET 2005
175	- aio_scandir errornously called callback twice in some cases.
176	- added AnyEvent example.
177
178	1.61 Wed Sep 7 19:40:42 CEST 2005
179	- no longer include $Config{libs}, as distros include too much
180	garbage in there that is not installed on typical systems
181	(for example, debian links perl against -lgdbm and many more
182	libraries despite perl not needing it, slowing down startup and
183	wasting memory).
184
185	1.6 Tue Aug 30 17:44:44 CEST 2005
186	- added aio_readdir, aio_scandir.
187	- added aio_sendfile, including sendfile emulation when sendfile
188	isn't available. Linux, FreeBSD and HP-UX might work (sendfilev
189	support is unavailable on my solaris 8 machine, but preliminary
190	code is there. What's lacking is configury stuff and testing...).
191
192	1.5 Sat Aug 20 02:32:19 CEST 2005
193	- create the aio threads on demand only (good after forking).
194	- somebody nagged about C89 compatibility, so this release should
195	be C89 compatible, but no guarantees for future ones.
196	- abort when the configure script fails.
197
198	1.4 Wed Aug 17 08:07:27 CEST 2005
199	- forgot to recreate the pipe after forking, this could cause
200	deadlocks.
201
202	1.3 Wed Aug 17 07:25:54 CEST 2005
203	- properly propagate exceptions from callbacks, instead of silently
204	eating them.
205	- use a different fork algorithm that avoids recursive callback
206	invocations and reduces fork latency in busy processes.
207	- fix a bug where the buffer scalar in aio_read got assigned the wrong
208	length after reading.
209	- fix a bug where the child would process some outstanding requests
210	from the parent.
211	- make a copy of the callback scalar, to avoid some very uncommon
212	(but valid) usages where the callback scalar changes.
213	- the callback was never freed in aio_read/aio_write.
214	- aio_read/aio_write will now set the readonly flag on the data
215	scalar for better error reporting.
216
217	1.2 Wed Aug 17 01:22:58 CEST 2005
218	- verified on cygwin, linux/amd64+ia32+alpha, solaris.
219	- use SvPVbyte for filenames now. You need to encode your strings to
220	the external filename encoding first.
221	- fix the bug where filehandles could leak (again).
222	- clarify freebsd situation: make it work and tell me how, or go away
223	with your underdocumented, broken and outdated OS.
224	- fork'ing should now be officially supported (where linux and
225	posix contradict each other, I followed posix).
226	- only call read() once per poll, not twice (speedup).
227	- new functions: aio_rmdir, aio_symlink.
228	- force callback arguments to be undef or a reference, for better
229	error catching.
230
231	1.1 Sun Aug 7 05:27:23 CEST 2005
232	- added configure script to detect availability of some calls.
233	(imperfect, as we cannot detect things like -lrt due to missing
234	feedback yet).
235	- emulate fdatasync via fsync, pread/pwrite via unsafe read/write
236	and readahead via manual reading on platforms lacking those.
237	- ported t/03_errors.t+framework by Brad Fitzpatrick
238	from Linux::AIO.
239	- removed XOPEN_SOURCE because stupid solaris 9 doesn't
240	compile with it enabled. Probably breaks others. Oh well.
241	- try to be more careful with errno on non-threaded perls.
242	- cygwins perl insisted on a matching open mode when morphing
243	the fd to an fh.
244	- convert sv's to "byte" encoding in aio_read/aio_write. Might
245	do that for pathnames, too, in the future, so make sure you
246	properly encode your pathnames.
247
248	1.0 Fri Jul 22 10:43:30 CEST 2005
249	- aio_open did not reliably deliver (open) filehandles.
250	- all aio_*-functions keep a reference to the filehandle so
251	it doesn't go away while the aio requests is working on it.
252	- disable warnings in AIO.pm.
253
254	0.9 Wed Jul 20 23:55:04 CEST 2005
255	- allow recursive calls to poll_cb, use less locking calls, too.
256	- fix the Gtk2-example in the SYNOPSIS.
257	- use pread/pwrite not pread64/pwrite64. this was simply a leftover
258	from Linux::AIO.
259	(found by compiling on cygwin. Unfortunately, cygwin declares but
260	does not implement pread/pwrite).
261	- only include <sys/syscall.h> on linux.
262
263	0.5 Tue Jul 12 13:03:09 CEST 2005
264	- removed #include <endian.h>, it's not portable, and we don't
265	need it anyway.
266	- link against -lrt, as it might contain goodies such as fdatasync,
267	and often aio_read, which we do not use yet, but it shouldn't hurt.
268
269	0.4 Mon Jul 11 05:28:25 CEST 2005
270	- added IO::AIO::flush, IO::AIO::poll.
271	- make callback argument optional for all calls.
272
273	0.3 Mon Jul 11 01:42:37 CEST 2005
274	- restructured manpage.
275	- added SYNOPSIS with examples for Event, Glib, Tk.
276	- remove explicit context support so I don't have to maintain
277	it for threaded perls (i.e. it should work now :).
278
279	0.2 Sun Jul 10 22:57:12 CEST 2005
280	- return immediately from poll_wait if nreqs==0.
281	- get rid of the request pipe and use faster thread-thread
282	communications for most requests and responses.
283
284	0.1
285	- cloned from Linux::AIO, which is very similar.
286