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Revision: 1.15
Committed: Thu Sep 13 21:34:00 2007 UTC (16 years, 8 months ago) by root
Branch: MAIN
Changes since 1.14: +48 -5 lines
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# Content
1 =head1 NAME
2
3 BDB - Asynchronous Berkeley DB access
4
5 =head1 SYNOPSIS
6
7 use BDB;
8
9 =head1 DESCRIPTION
10
11 See the BerkeleyDB documentation (L<http://www.oracle.com/technology/documentation/berkeley-db/db/index.html>).
12 The BDB API is very similar to the C API (the translation has been very faithful).
13
14 See also the example sections in the document below and possibly the eg/
15 subdirectory of the BDB distribution. Last not least see the IO::AIO
16 documentation, as that module uses almost the same asynchronous request
17 model as this module.
18
19 I know this is woefully inadequate documentation. Send a patch!
20
21
22 =head1 REQUEST ANATOMY AND LIFETIME
23
24 Every request method creates a request. which is a C data structure not
25 directly visible to Perl.
26
27 During their existance, bdb requests travel through the following states,
28 in order:
29
30 =over 4
31
32 =item ready
33
34 Immediately after a request is created it is put into the ready state,
35 waiting for a thread to execute it.
36
37 =item execute
38
39 A thread has accepted the request for processing and is currently
40 executing it (e.g. blocking in read).
41
42 =item pending
43
44 The request has been executed and is waiting for result processing.
45
46 While request submission and execution is fully asynchronous, result
47 processing is not and relies on the perl interpreter calling C<poll_cb>
48 (or another function with the same effect).
49
50 =item result
51
52 The request results are processed synchronously by C<poll_cb>.
53
54 The C<poll_cb> function will process all outstanding aio requests by
55 calling their callbacks, freeing memory associated with them and managing
56 any groups they are contained in.
57
58 =item done
59
60 Request has reached the end of its lifetime and holds no resources anymore
61 (except possibly for the Perl object, but its connection to the actual
62 aio request is severed and calling its methods will either do nothing or
63 result in a runtime error).
64
65 =back
66
67 =cut
68
69 package BDB;
70
71 no warnings;
72 use strict 'vars';
73
74 use base 'Exporter';
75
76 BEGIN {
77 our $VERSION = '1.1';
78
79 our @BDB_REQ = qw(
80 db_env_open db_env_close db_env_txn_checkpoint db_env_lock_detect
81 db_env_memp_sync db_env_memp_trickle
82 db_open db_close db_compact db_sync db_put db_get db_pget db_del db_key_range
83 db_txn_commit db_txn_abort db_txn_finish
84 db_c_close db_c_count db_c_put db_c_get db_c_pget db_c_del
85 db_sequence_open db_sequence_close
86 db_sequence_get db_sequence_remove
87 );
88 our @EXPORT = (@BDB_REQ, qw(dbreq_pri dbreq_nice db_env_create db_create));
89 our @EXPORT_OK = qw(
90 poll_fileno poll_cb poll_wait flush
91 min_parallel max_parallel max_idle
92 nreqs nready npending nthreads
93 max_poll_time max_poll_reqs
94 );
95
96 require XSLoader;
97 XSLoader::load ("BDB", $VERSION);
98 }
99
100 =head2 BERKELEYDB FUNCTIONS
101
102 All of these are functions. The create functions simply return a new
103 object and never block. All the remaining functions all take an optional
104 callback as last argument. If it is missing, then the fucntion will be
105 executed synchronously.
106
107 BDB functions that cannot block (mostly functions that manipulate
108 settings) are method calls on the relevant objects, so the rule of thumb
109 is: if its a method, its not blocking, if its a function, it takes a
110 callback as last argument.
111
112 In the following, C<$int> signifies an integer return value,
113 C<octetstring> is a "binary string" (i.e. a perl string with no character
114 indices >255), C<U32> is an unsigned 32 bit integer, C<int> is some
115 integer, C<NV> is a floating point value.
116
117 The C<SV *> types are generic perl scalars (for input and output of data
118 values), and the C<SV *callback> is the optional callback function to call
119 when the request is completed.
120
121 The various C<DB_ENV> etc. arguments are handles return by
122 C<db_env_create>, C<db_create>, C<txn_begin> and so on. If they have an
123 appended C<_ornull> this means they are optional and you can pass C<undef>
124 for them, resulting a NULL pointer on the C level.
125
126 =head3 BDB functions
127
128 Functions in the BDB namespace, exported by default:
129
130 $env = db_env_create (U32 env_flags = 0)
131 flags: RPCCLIENT
132
133 db_env_open (DB_ENV *env, octetstring db_home, U32 open_flags, int mode, SV *callback = &PL_sv_undef)
134 open_flags: INIT_CDB INIT_LOCK INIT_LOG INIT_MPOOL INIT_REP INIT_TXN RECOVER RECOVER_FATAL USE_ENVIRON USE_ENVIRON_ROOT CREATE LOCKDOWN PRIVATE REGISTER SYSTEM_MEM
135 db_env_close (DB_ENV *env, U32 flags = 0, SV *callback = &PL_sv_undef)
136 db_env_txn_checkpoint (DB_ENV *env, U32 kbyte = 0, U32 min = 0, U32 flags = 0, SV *callback = &PL_sv_undef)
137 flags: FORCE
138 db_env_lock_detect (DB_ENV *env, U32 flags = 0, U32 atype = DB_LOCK_DEFAULT, SV *dummy = 0, SV *callback = &PL_sv_undef)
139 atype: LOCK_DEFAULT LOCK_EXPIRE LOCK_MAXLOCKS LOCK_MAXWRITE LOCK_MINLOCKS LOCK_MINWRITE LOCK_OLDEST LOCK_RANDOM LOCK_YOUNGEST
140 db_env_memp_sync (DB_ENV *env, SV *dummy = 0, SV *callback = &PL_sv_undef)
141 db_env_memp_trickle (DB_ENV *env, int percent, SV *dummy = 0, SV *callback = &PL_sv_undef)
142
143 $db = db_create (DB_ENV *env = 0, U32 flags = 0)
144 flags: XA_CREATE
145
146 db_open (DB *db, DB_TXN_ornull *txnid, octetstring file, octetstring database, int type, U32 flags, int mode, SV *callback = &PL_sv_undef)
147 flags: AUTO_COMMIT CREATE EXCL MULTIVERSION NOMMAP RDONLY READ_UNCOMMITTED THREAD TRUNCATE
148 db_close (DB *db, U32 flags = 0, SV *callback = &PL_sv_undef)
149 flags: DB_NOSYNC
150 db_compact (DB *db, DB_TXN_ornull *txn = 0, SV *start = 0, SV *stop = 0, SV *unused1 = 0, U32 flags = DB_FREE_SPACE, SV *unused2 = 0, SV *callback = &PL_sv_undef)
151 flags: FREELIST_ONLY FREE_SPACE
152 db_sync (DB *db, U32 flags = 0, SV *callback = &PL_sv_undef)
153 db_key_range (DB *db, DB_TXN_ornull *txn, SV *key, SV *key_range, U32 flags = 0, SV *callback = &PL_sv_undef)
154 db_put (DB *db, DB_TXN_ornull *txn, SV *key, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef)
155 flags: APPEND NODUPDATA NOOVERWRITE
156 db_get (DB *db, DB_TXN_ornull *txn, SV *key, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef)
157 flags: CONSUME CONSUME_WAIT GET_BOTH SET_RECNO MULTIPLE READ_COMMITTED READ_UNCOMMITTED RMW
158 db_pget (DB *db, DB_TXN_ornull *txn, SV *key, SV *pkey, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef)
159 flags: CONSUME CONSUME_WAIT GET_BOTH SET_RECNO MULTIPLE READ_COMMITTED READ_UNCOMMITTED RMW
160 db_del (DB *db, DB_TXN_ornull *txn, SV *key, U32 flags = 0, SV *callback = &PL_sv_undef)
161 db_txn_commit (DB_TXN *txn, U32 flags = 0, SV *callback = &PL_sv_undef)
162 flags: TXN_NOSYNC TXN_SYNC
163 db_txn_abort (DB_TXN *txn, SV *callback = &PL_sv_undef)
164
165 db_c_close (DBC *dbc, SV *callback = &PL_sv_undef)
166 db_c_count (DBC *dbc, SV *count, U32 flags = 0, SV *callback = &PL_sv_undef)
167 db_c_put (DBC *dbc, SV *key, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef)
168 flags: AFTER BEFORE CURRENT KEYFIRST KEYLAST NODUPDATA
169 db_c_get (DBC *dbc, SV *key, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef)
170 flags: CURRENT FIRST GET_BOTH GET_BOTH_RANGE GET_RECNO JOIN_ITEM LAST NEXT NEXT_DUP NEXT_NODUP PREV PREV_DUP PREV_NODUP SET SET_RANGE SET_RECNO READ_UNCOMMITTED MULTIPLE MULTIPLE_KEY RMW
171 db_c_pget (DBC *dbc, SV *key, SV *pkey, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef)
172 db_c_del (DBC *dbc, U32 flags = 0, SV *callback = &PL_sv_undef)
173
174 db_sequence_open (DB_SEQUENCE *seq, DB_TXN_ornull *txnid, SV *key, U32 flags = 0, SV *callback = &PL_sv_undef)
175 flags: CREATE EXCL
176 db_sequence_close (DB_SEQUENCE *seq, U32 flags = 0, SV *callback = &PL_sv_undef)
177 db_sequence_get (DB_SEQUENCE *seq, DB_TXN_ornull *txnid, int delta, SV *seq_value, U32 flags = DB_TXN_NOSYNC, SV *callback = &PL_sv_undef)
178 flags: TXN_NOSYNC
179 db_sequence_remove (DB_SEQUENCE *seq, DB_TXN_ornull *txnid = 0, U32 flags = 0, SV *callback = &PL_sv_undef)
180 flags: TXN_NOSYNC
181
182 =head4 db_txn_finish (DB_TXN *txn, U32 flags = 0, SV *callback = &PL_sv_undef)
183
184 This is not a Berkeley DB function but a BDB module extension. It is very
185 annoying to have to check every single BDB function for error returns and
186 provide a codepath out of your transaction. While the BDB module still
187 makes this possible, it contains the following extensions:
188
189 When a transaction-protected function returns any operating system
190 error (errno > 0), BDB will set the C<TXN_DEADLOCK> flag on the
191 transaction. This flag is also set by Berkeley DB functions externally
192 when an operation fails with LOCK_DEADLOCK, and it causes all further
193 operations on that transaction (including C<db_txn_commit>) to fail.
194
195 The C<db_txn_finish> request will look at this flag, and, if it is set,
196 will automatically call C<db_txn_abort> (setting errno to C<LOCK_DEADLOCK>
197 if it isn't set). If it isn't set, it will call C<db_txn_commit> and
198 return the error normally.
199
200 How to use this? Easy: just write your transaction normally:
201
202 my $txn = $db_env->txn_begin;
203 db_get $db, $txn, "key", my $data;
204 db_put $db, $txn, "key", $data + 1 unless $! == BDB::NOTFOUND;
205 db_txn_finish $txn;
206 die "transaction failed" if $!;
207
208 That is, handle only the expected errors. If something unexpected happens
209 (EIO, LOCK_NOTGRANTED or a deadlock in either db_get or db_put), then the remaining
210 requests (db_put in this case) will simply be skipped (they will fail with
211 LOCK_DEADLOCK) and the transaction will be aborted.
212
213 You cna use the C<< $txn->failed >> method to check wether a transaction
214 has failed in this way and abort further processing (excluding
215 C<db_txn_finish>).
216
217 =head3 DB_ENV/database environment methods
218
219 Methods available on DB_ENV/$env handles:
220
221 DESTROY (DB_ENV_ornull *env)
222 CODE:
223 if (env)
224 env->close (env, 0);
225
226 $int = $env->set_data_dir (const char *dir)
227 $int = $env->set_tmp_dir (const char *dir)
228 $int = $env->set_lg_dir (const char *dir)
229 $int = $env->set_shm_key (long shm_key)
230 $int = $env->set_cachesize (U32 gbytes, U32 bytes, int ncache = 0)
231 $int = $env->set_flags (U32 flags, int onoff)
232 $env->set_errfile (FILE *errfile = 0)
233 $env->set_msgfile (FILE *msgfile = 0)
234 $int = $env->set_verbose (U32 which, int onoff = 1)
235 $int = $env->set_encrypt (const char *password, U32 flags = 0)
236 $int = $env->set_timeout (NV timeout_seconds, U32 flags = SET_TXN_TIMEOUT)
237 $int = $env->set_mp_max_openfd (int maxopenfd);
238 $int = $env->set_mp_max_write (int maxwrite, int maxwrite_sleep);
239 $int = $env->set_mp_mmapsize (int mmapsize_mb)
240 $int = $env->set_lk_detect (U32 detect = DB_LOCK_DEFAULT)
241 $int = $env->set_lk_max_lockers (U32 max)
242 $int = $env->set_lk_max_locks (U32 max)
243 $int = $env->set_lk_max_objects (U32 max)
244 $int = $env->set_lg_bsize (U32 max)
245 $int = $env->set_lg_max (U32 max)
246
247 $txn = $env->txn_begin (DB_TXN_ornull *parent = 0, U32 flags = 0)
248 flags: READ_COMMITTED READ_UNCOMMITTED TXN_NOSYNC TXN_NOWAIT TXN_SNAPSHOT TXN_SYNC TXN_WAIT TXN_WRITE_NOSYNC
249
250 =head4 Example:
251
252 use AnyEvent;
253 use BDB;
254
255 our $FH; open $FH, "<&=" . BDB::poll_fileno;
256 our $WATCHER = AnyEvent->io (fh => $FH, poll => 'r', cb => \&BDB::poll_cb);
257
258 BDB::min_parallel 8;
259
260 my $env = db_env_create;
261
262 mkdir "bdtest", 0700;
263 db_env_open
264 $env,
265 "bdtest",
266 BDB::INIT_LOCK | BDB::INIT_LOG | BDB::INIT_MPOOL | BDB::INIT_TXN | BDB::RECOVER | BDB::USE_ENVIRON | BDB::CREATE,
267 0600;
268
269 $env->set_flags (BDB::AUTO_COMMIT | BDB::TXN_NOSYNC, 1);
270
271
272 =head3 DB/database methods
273
274 Methods available on DB/$db handles:
275
276 DESTROY (DB_ornull *db)
277 CODE:
278 if (db)
279 {
280 SV *env = (SV *)db->app_private;
281 db->close (db, 0);
282 SvREFCNT_dec (env);
283 }
284
285 $int = $db->set_cachesize (U32 gbytes, U32 bytes, int ncache = 0)
286 $int = $db->set_flags (U32 flags)
287 flags: CHKSUM ENCRYPT TXN_NOT_DURABLE
288 Btree: DUP DUPSORT RECNUM REVSPLITOFF
289 Hash: DUP DUPSORT
290 Queue: INORDER
291 Recno: RENUMBER SNAPSHOT
292
293 $int = $db->set_encrypt (const char *password, U32 flags)
294 $int = $db->set_lorder (int lorder)
295 $int = $db->set_bt_minkey (U32 minkey)
296 $int = $db->set_re_delim (int delim)
297 $int = $db->set_re_pad (int re_pad)
298 $int = $db->set_re_source (char *source)
299 $int = $db->set_re_len (U32 re_len)
300 $int = $db->set_h_ffactor (U32 h_ffactor)
301 $int = $db->set_h_nelem (U32 h_nelem)
302 $int = $db->set_q_extentsize (U32 extentsize)
303
304 $dbc = $db->cursor (DB_TXN_ornull *txn = 0, U32 flags = 0)
305 flags: READ_COMMITTED READ_UNCOMMITTED WRITECURSOR TXN_SNAPSHOT
306 $seq = $db->sequence (U32 flags = 0)
307
308 =head4 Example:
309
310 my $db = db_create $env;
311 db_open $db, undef, "table", undef, BDB::BTREE, BDB::AUTO_COMMIT | BDB::CREATE | BDB::READ_UNCOMMITTED, 0600;
312
313 for (1..1000) {
314 db_put $db, undef, "key $_", "data $_";
315
316 db_key_range $db, undef, "key $_", my $keyrange;
317 my ($lt, $eq, $gt) = @$keyrange;
318 }
319
320 db_del $db, undef, "key $_" for 1..1000;
321
322 db_sync $db;
323
324
325 =head3 DB_TXN/transaction methods
326
327 Methods available on DB_TXN/$txn handles:
328
329 DESTROY (DB_TXN_ornull *txn)
330 CODE:
331 if (txn)
332 txn->abort (txn);
333
334 $int = $txn->set_timeout (NV timeout_seconds, U32 flags = SET_TXN_TIMEOUT)
335 flags: SET_LOCK_TIMEOUT SET_TXN_TIMEOUT
336
337 $bool = $txn->failed
338 # see db_txn_finish documentation, above
339
340
341 =head3 DBC/cursor methods
342
343 Methods available on DBC/$dbc handles:
344
345 DESTROY (DBC_ornull *dbc)
346 CODE:
347 if (dbc)
348 dbc->c_close (dbc);
349
350 =head4 Example:
351
352 my $c = $db->cursor;
353
354 for (;;) {
355 db_c_get $c, my $key, my $data, BDB::NEXT;
356 warn "<$!,$key,$data>";
357 last if $!;
358 }
359
360 db_c_close $c;
361
362
363 =head3 DB_SEQUENCE/sequence methods
364
365 Methods available on DB_SEQUENCE/$seq handles:
366
367 DESTROY (DB_SEQUENCE_ornull *seq)
368 CODE:
369 if (seq)
370 seq->close (seq, 0);
371
372 $int = $seq->initial_value (db_seq_t value)
373 $int = $seq->set_cachesize (U32 size)
374 $int = $seq->set_flags (U32 flags)
375 flags: SEQ_DEC SEQ_INC SEQ_WRAP
376 $int = $seq->set_range (db_seq_t min, db_seq_t max)
377
378 =head4 Example:
379
380 my $seq = $db->sequence;
381
382 db_sequence_open $seq, undef, "seq", BDB::CREATE;
383 db_sequence_get $seq, undef, 1, my $value;
384
385
386 =head2 SUPPORT FUNCTIONS
387
388 =head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
389
390 =over 4
391
392 =item $fileno = BDB::poll_fileno
393
394 Return the I<request result pipe file descriptor>. This filehandle must be
395 polled for reading by some mechanism outside this module (e.g. Event or
396 select, see below or the SYNOPSIS). If the pipe becomes readable you have
397 to call C<poll_cb> to check the results.
398
399 See C<poll_cb> for an example.
400
401 =item BDB::poll_cb
402
403 Process some outstanding events on the result pipe. You have to call this
404 regularly. Returns the number of events processed. Returns immediately
405 when no events are outstanding. The amount of events processed depends on
406 the settings of C<BDB::max_poll_req> and C<BDB::max_poll_time>.
407
408 If not all requests were processed for whatever reason, the filehandle
409 will still be ready when C<poll_cb> returns.
410
411 Example: Install an Event watcher that automatically calls
412 BDB::poll_cb with high priority:
413
414 Event->io (fd => BDB::poll_fileno,
415 poll => 'r', async => 1,
416 cb => \&BDB::poll_cb);
417
418 =item BDB::max_poll_reqs $nreqs
419
420 =item BDB::max_poll_time $seconds
421
422 These set the maximum number of requests (default C<0>, meaning infinity)
423 that are being processed by C<BDB::poll_cb> in one call, respectively
424 the maximum amount of time (default C<0>, meaning infinity) spent in
425 C<BDB::poll_cb> to process requests (more correctly the mininum amount
426 of time C<poll_cb> is allowed to use).
427
428 Setting C<max_poll_time> to a non-zero value creates an overhead of one
429 syscall per request processed, which is not normally a problem unless your
430 callbacks are really really fast or your OS is really really slow (I am
431 not mentioning Solaris here). Using C<max_poll_reqs> incurs no overhead.
432
433 Setting these is useful if you want to ensure some level of
434 interactiveness when perl is not fast enough to process all requests in
435 time.
436
437 For interactive programs, values such as C<0.01> to C<0.1> should be fine.
438
439 Example: Install an Event watcher that automatically calls
440 BDB::poll_cb with low priority, to ensure that other parts of the
441 program get the CPU sometimes even under high AIO load.
442
443 # try not to spend much more than 0.1s in poll_cb
444 BDB::max_poll_time 0.1;
445
446 # use a low priority so other tasks have priority
447 Event->io (fd => BDB::poll_fileno,
448 poll => 'r', nice => 1,
449 cb => &BDB::poll_cb);
450
451 =item BDB::poll_wait
452
453 If there are any outstanding requests and none of them in the result
454 phase, wait till the result filehandle becomes ready for reading (simply
455 does a C<select> on the filehandle. This is useful if you want to
456 synchronously wait for some requests to finish).
457
458 See C<nreqs> for an example.
459
460 =item BDB::poll
461
462 Waits until some requests have been handled.
463
464 Returns the number of requests processed, but is otherwise strictly
465 equivalent to:
466
467 BDB::poll_wait, BDB::poll_cb
468
469 =item BDB::flush
470
471 Wait till all outstanding AIO requests have been handled.
472
473 Strictly equivalent to:
474
475 BDB::poll_wait, BDB::poll_cb
476 while BDB::nreqs;
477
478 =back
479
480 =head3 CONTROLLING THE NUMBER OF THREADS
481
482 =over 4
483
484 =item BDB::min_parallel $nthreads
485
486 Set the minimum number of AIO threads to C<$nthreads>. The current
487 default is C<8>, which means eight asynchronous operations can execute
488 concurrently at any one time (the number of outstanding requests,
489 however, is unlimited).
490
491 BDB starts threads only on demand, when an AIO request is queued and
492 no free thread exists. Please note that queueing up a hundred requests can
493 create demand for a hundred threads, even if it turns out that everything
494 is in the cache and could have been processed faster by a single thread.
495
496 It is recommended to keep the number of threads relatively low, as some
497 Linux kernel versions will scale negatively with the number of threads
498 (higher parallelity => MUCH higher latency). With current Linux 2.6
499 versions, 4-32 threads should be fine.
500
501 Under most circumstances you don't need to call this function, as the
502 module selects a default that is suitable for low to moderate load.
503
504 =item BDB::max_parallel $nthreads
505
506 Sets the maximum number of AIO threads to C<$nthreads>. If more than the
507 specified number of threads are currently running, this function kills
508 them. This function blocks until the limit is reached.
509
510 While C<$nthreads> are zero, aio requests get queued but not executed
511 until the number of threads has been increased again.
512
513 This module automatically runs C<max_parallel 0> at program end, to ensure
514 that all threads are killed and that there are no outstanding requests.
515
516 Under normal circumstances you don't need to call this function.
517
518 =item BDB::max_idle $nthreads
519
520 Limit the number of threads (default: 4) that are allowed to idle (i.e.,
521 threads that did not get a request to process within 10 seconds). That
522 means if a thread becomes idle while C<$nthreads> other threads are also
523 idle, it will free its resources and exit.
524
525 This is useful when you allow a large number of threads (e.g. 100 or 1000)
526 to allow for extremely high load situations, but want to free resources
527 under normal circumstances (1000 threads can easily consume 30MB of RAM).
528
529 The default is probably ok in most situations, especially if thread
530 creation is fast. If thread creation is very slow on your system you might
531 want to use larger values.
532
533 =item $oldmaxreqs = BDB::max_outstanding $maxreqs
534
535 This is a very bad function to use in interactive programs because it
536 blocks, and a bad way to reduce concurrency because it is inexact: Better
537 use an C<aio_group> together with a feed callback.
538
539 Sets the maximum number of outstanding requests to C<$nreqs>. If you
540 to queue up more than this number of requests, the next call to the
541 C<poll_cb> (and C<poll_some> and other functions calling C<poll_cb>)
542 function will block until the limit is no longer exceeded.
543
544 The default value is very large, so there is no practical limit on the
545 number of outstanding requests.
546
547 You can still queue as many requests as you want. Therefore,
548 C<max_oustsanding> is mainly useful in simple scripts (with low values) or
549 as a stop gap to shield against fatal memory overflow (with large values).
550
551 =item BDB::set_sync_prepare $cb
552
553 Sets a callback that is called whenever a request is created without an
554 explicit callback. It has to return two code references. The first is used
555 as the request callback, and the second is called to wait until the first
556 callback has been called. The default implementation works like this:
557
558 sub {
559 my $status;
560 (
561 sub { $status = $! },
562 sub { BDB::poll while !defined $status; $! = $status },
563 )
564 }
565
566 =back
567
568 =head3 STATISTICAL INFORMATION
569
570 =over 4
571
572 =item BDB::nreqs
573
574 Returns the number of requests currently in the ready, execute or pending
575 states (i.e. for which their callback has not been invoked yet).
576
577 Example: wait till there are no outstanding requests anymore:
578
579 BDB::poll_wait, BDB::poll_cb
580 while BDB::nreqs;
581
582 =item BDB::nready
583
584 Returns the number of requests currently in the ready state (not yet
585 executed).
586
587 =item BDB::npending
588
589 Returns the number of requests currently in the pending state (executed,
590 but not yet processed by poll_cb).
591
592 =back
593
594 =cut
595
596 set_sync_prepare {
597 my $status;
598 (
599 sub {
600 $status = $!;
601 },
602 sub {
603 BDB::poll while !defined $status;
604 $! = $status;
605 },
606 )
607 };
608
609 min_parallel 8;
610
611 END { flush }
612
613 1;
614
615 =head2 FORK BEHAVIOUR
616
617 This module should do "the right thing" when the process using it forks:
618
619 Before the fork, IO::AIO enters a quiescent state where no requests
620 can be added in other threads and no results will be processed. After
621 the fork the parent simply leaves the quiescent state and continues
622 request/result processing, while the child frees the request/result queue
623 (so that the requests started before the fork will only be handled in the
624 parent). Threads will be started on demand until the limit set in the
625 parent process has been reached again.
626
627 In short: the parent will, after a short pause, continue as if fork had
628 not been called, while the child will act as if IO::AIO has not been used
629 yet.
630
631 =head2 MEMORY USAGE
632
633 Per-request usage:
634
635 Each aio request uses - depending on your architecture - around 100-200
636 bytes of memory. In addition, stat requests need a stat buffer (possibly
637 a few hundred bytes), readdir requires a result buffer and so on. Perl
638 scalars and other data passed into aio requests will also be locked and
639 will consume memory till the request has entered the done state.
640
641 This is not awfully much, so queuing lots of requests is not usually a
642 problem.
643
644 Per-thread usage:
645
646 In the execution phase, some aio requests require more memory for
647 temporary buffers, and each thread requires a stack and other data
648 structures (usually around 16k-128k, depending on the OS).
649
650 =head1 KNOWN BUGS
651
652 Known bugs will be fixed in the next release, except:
653
654 If you use a transaction in any request, and the request returns
655 with an operating system error or DB_LOCK_NOTGRANTED, the internal
656 TXN_DEADLOCK flag will be set on the transaction. See C<db_txn_finish>,
657 above.
658
659 =head1 SEE ALSO
660
661 L<Coro::AIO>.
662
663 =head1 AUTHOR
664
665 Marc Lehmann <schmorp@schmorp.de>
666 http://home.schmorp.de/
667
668 =cut
669