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Comparing BDB/BDB.pm (file contents):
Revision 1.14 by root, Thu Sep 13 12:29:49 2007 UTC vs.
Revision 1.38 by root, Mon Jul 7 22:11:04 2008 UTC

… …
3BDB - Asynchronous Berkeley DB access 3BDB - Asynchronous Berkeley DB access
4 4
5=head1 SYNOPSIS 5=head1 SYNOPSIS
6 6
7 use BDB; 7 use BDB;
8
9 my $env = db_env_create;
10
11 mkdir "bdtest", 0700;
12 db_env_open
13 $env,
14 "bdtest",
15 BDB::INIT_LOCK | BDB::INIT_LOG | BDB::INIT_MPOOL
16 | BDB::INIT_TXN | BDB::RECOVER | BDB::USE_ENVIRON | BDB::CREATE,
17 0600;
18
19 $env->set_flags (BDB::AUTO_COMMIT | BDB::TXN_NOSYNC, 1);
20
21 my $db = db_create $env;
22 db_open $db, undef, "table", undef, BDB::BTREE, BDB::AUTO_COMMIT | BDB::CREATE
23 | BDB::READ_UNCOMMITTED, 0600;
24 db_put $db, undef, "key", "data", 0, sub {
25 db_del $db, undef, "key";
26 };
27 db_sync $db;
28
29 # when you also use Coro, management is easy:
30 use Coro::BDB;
31
32 # automatic event loop intergration with AnyEvent:
33 use AnyEvent::BDB;
34
35 # automatic result processing with EV:
36 my $WATCHER = EV::io BDB::poll_fileno, EV::READ, \&BDB::poll_cb;
37
38 # with Glib:
39 add_watch Glib::IO BDB::poll_fileno,
40 in => sub { BDB::poll_cb; 1 };
41
42 # or simply flush manually
43 BDB::flush;
44
8 45
9=head1 DESCRIPTION 46=head1 DESCRIPTION
10 47
11See the BerkeleyDB documentation (L<http://www.oracle.com/technology/documentation/berkeley-db/db/index.html>). 48See the BerkeleyDB documentation (L<http://www.oracle.com/technology/documentation/berkeley-db/db/index.html>).
12The BDB API is very similar to the C API (the translation has been very faithful). 49The BDB API is very similar to the C API (the translation has been very faithful).
… …
72use strict 'vars'; 109use strict 'vars';
73 110
74use base 'Exporter'; 111use base 'Exporter';
75 112
76BEGIN { 113BEGIN {
77 our $VERSION = '1.0'; 114 our $VERSION = '1.5';
78 115
79 our @BDB_REQ = qw( 116 our @BDB_REQ = qw(
80 db_env_open db_env_close db_env_txn_checkpoint db_env_lock_detect 117 db_env_open db_env_close db_env_txn_checkpoint db_env_lock_detect
81 db_env_memp_sync db_env_memp_trickle 118 db_env_memp_sync db_env_memp_trickle db_env_dbrename db_env_dbremove
82 db_open db_close db_compact db_sync db_put db_get db_pget db_del db_key_range 119 db_open db_close db_compact db_sync db_upgrade
120 db_put db_get db_pget db_del db_key_range
83 db_txn_commit db_txn_abort 121 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 122 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 123 db_sequence_open db_sequence_close
86 db_sequence_get db_sequence_remove 124 db_sequence_get db_sequence_remove
87 ); 125 );
88 our @EXPORT = (@BDB_REQ, qw(dbreq_pri dbreq_nice db_env_create db_create)); 126 our @EXPORT = (@BDB_REQ, qw(dbreq_pri dbreq_nice db_env_create db_create));
… …
95 133
96 require XSLoader; 134 require XSLoader;
97 XSLoader::load ("BDB", $VERSION); 135 XSLoader::load ("BDB", $VERSION);
98} 136}
99 137
138=head2 WIN32 FILENAMES/DATABASE NAME MESS
139
140Perl on Win32 supports only ASCII filenames (the reason is that it abuses
141an internal flag to store wether a filename is Unicode or ANSI, but that
142flag is used for somethign else in the perl core, so there is no way to
143detect wether a filename is ANSI or Unicode-encoded). The BDB module
144tries to work around this issue by assuming that the filename is an ANSI
145filename and BDB was built for unicode support.
146
100=head2 BERKELEYDB FUNCTIONS 147=head2 BERKELEYDB FUNCTIONS
101 148
102All of these are functions. The create functions simply return a new 149All of these are functions. The create functions simply return a new
103object and never block. All the remaining functions all take an optional 150object and never block. All the remaining functions take an optional
104callback as last argument. If it is missing, then the fucntion will be 151callback as last argument. If it is missing, then the function will be
105executed synchronously. 152executed synchronously. In both cases, C<$!> will reflect the return value
153of the function.
106 154
107BDB functions that cannot block (mostly functions that manipulate 155BDB functions that cannot block (mostly functions that manipulate
108settings) are method calls on the relevant objects, so the rule of thumb 156settings) are method calls on the relevant objects, so the rule of thumb
109is: if its a method, its not blocking, if its a function, it takes a 157is: if it's a method, it's not blocking, if it's a function, it takes a
110callback as last argument. 158callback as last argument.
111 159
112In the following, C<$int> signifies an integer return value, 160In the following, C<$int> signifies an integer return value,
113C<octetstring> is a "binary string" (i.e. a perl string with no character 161C<bdb_filename> is a "filename" (octets on unix, madness on windows),
114indices >255), C<U32> is an unsigned 32 bit integer, C<int> is some 162C<U32> is an unsigned 32 bit integer, C<int> is some integer, C<NV> is a
115integer, C<NV> is a floating point value. 163floating point value.
116 164
117The C<SV *> types are generic perl scalars (for input and output of data 165The C<SV *> types are generic perl scalars (for input and output of data
118values), and the C<SV *callback> is the optional callback function to call 166values), and the C<SV *callback> is the optional callback function to call
119when the request is completed. 167when the request is completed.
120 168
… …
128Functions in the BDB namespace, exported by default: 176Functions in the BDB namespace, exported by default:
129 177
130 $env = db_env_create (U32 env_flags = 0) 178 $env = db_env_create (U32 env_flags = 0)
131 flags: RPCCLIENT 179 flags: RPCCLIENT
132 180
133 db_env_open (DB_ENV *env, octetstring db_home, U32 open_flags, int mode, SV *callback = &PL_sv_undef) 181 db_env_open (DB_ENV *env, bdb_filename 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 182 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) 183 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) 184 db_env_txn_checkpoint (DB_ENV *env, U32 kbyte = 0, U32 min = 0, U32 flags = 0, SV *callback = &PL_sv_undef)
137 flags: FORCE 185 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) 186 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 187 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) 188 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) 189 db_env_memp_trickle (DB_ENV *env, int percent, SV *dummy = 0, SV *callback = &PL_sv_undef)
190 db_env_dbremove (DB_ENV *env, DB_TXN_ornull *txnid, bdb_filename file, bdb_filename database, U32 flags = 0, SV *callback = &PL_sv_undef)
191 db_env_dbrename (DB_ENV *env, DB_TXN_ornull *txnid, bdb_filename file, bdb_filename database, bdb_filename newname, U32 flags = 0, SV *callback = &PL_sv_undef)
142 192
143 $db = db_create (DB_ENV *env = 0, U32 flags = 0) 193 $db = db_create (DB_ENV *env = 0, U32 flags = 0)
144 flags: XA_CREATE 194 flags: XA_CREATE
145 195
146 db_open (DB *db, DB_TXN_ornull *txnid, octetstring file, octetstring database, int type, U32 flags, int mode, SV *callback = &PL_sv_undef) 196 db_open (DB *db, DB_TXN_ornull *txnid, bdb_filename file, bdb_filename 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 197 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) 198 db_close (DB *db, U32 flags = 0, SV *callback = &PL_sv_undef)
149 flags: DB_NOSYNC 199 flags: DB_NOSYNC
200 db_upgrade (DB *db, bdb_filename file, U32 flags = 0, SV *callback = &PL_sv_undef)
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) 201 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 202 flags: FREELIST_ONLY FREE_SPACE
152 db_sync (DB *db, U32 flags = 0, SV *callback = &PL_sv_undef) 203 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) 204 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) 205 db_put (DB *db, DB_TXN_ornull *txn, SV *key, SV *data, 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) 228 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 229 flags: TXN_NOSYNC
179 db_sequence_remove (DB_SEQUENCE *seq, DB_TXN_ornull *txnid = 0, U32 flags = 0, SV *callback = &PL_sv_undef) 230 db_sequence_remove (DB_SEQUENCE *seq, DB_TXN_ornull *txnid = 0, U32 flags = 0, SV *callback = &PL_sv_undef)
180 flags: TXN_NOSYNC 231 flags: TXN_NOSYNC
181 232
233=head4 db_txn_finish (DB_TXN *txn, U32 flags = 0, SV *callback = &PL_sv_undef)
234
235This is not actually a Berkeley DB function but a BDB module
236extension. The background for this exytension is: It is very annoying to
237have to check every single BDB function for error returns and provide a
238codepath out of your transaction. While the BDB module still makes this
239possible, it contains the following extensions:
240
241When a transaction-protected function returns any operating system
242error (errno > 0), BDB will set the C<TXN_DEADLOCK> flag on the
243transaction. This flag is also set by Berkeley DB functions themselves
244when an operation fails with LOCK_DEADLOCK, and it causes all further
245operations on that transaction (including C<db_txn_commit>) to fail.
246
247The C<db_txn_finish> request will look at this flag, and, if it is set,
248will automatically call C<db_txn_abort> (setting errno to C<LOCK_DEADLOCK>
249if it isn't set to something else yet). If it isn't set, it will call
250C<db_txn_commit> and return the error normally.
251
252How to use this? Easy: just write your transaction normally:
253
254 my $txn = $db_env->txn_begin;
255 db_get $db, $txn, "key", my $data;
256 db_put $db, $txn, "key", $data + 1 unless $! == BDB::NOTFOUND;
257 db_txn_finish $txn;
258 die "transaction failed" if $!;
259
260That is, handle only the expected errors. If something unexpected happens
261(EIO, LOCK_NOTGRANTED or a deadlock in either db_get or db_put), then the remaining
262requests (db_put in this case) will simply be skipped (they will fail with
263LOCK_DEADLOCK) and the transaction will be aborted.
264
265You can use the C<< $txn->failed >> method to check wether a transaction
266has failed in this way and abort further processing (excluding
267C<db_txn_finish>).
268
182=head3 DB_ENV/database environment methods 269=head3 DB_ENV/database environment methods
183 270
184Methods available on DB_ENV/$env handles: 271Methods available on DB_ENV/$env handles:
185 272
186 DESTROY (DB_ENV_ornull *env) 273 DESTROY (DB_ENV_ornull *env)
… …
196 $int = $env->set_flags (U32 flags, int onoff) 283 $int = $env->set_flags (U32 flags, int onoff)
197 $env->set_errfile (FILE *errfile = 0) 284 $env->set_errfile (FILE *errfile = 0)
198 $env->set_msgfile (FILE *msgfile = 0) 285 $env->set_msgfile (FILE *msgfile = 0)
199 $int = $env->set_verbose (U32 which, int onoff = 1) 286 $int = $env->set_verbose (U32 which, int onoff = 1)
200 $int = $env->set_encrypt (const char *password, U32 flags = 0) 287 $int = $env->set_encrypt (const char *password, U32 flags = 0)
201 $int = $env->set_timeout (NV timeout, U32 flags) 288 $int = $env->set_timeout (NV timeout_seconds, U32 flags = SET_TXN_TIMEOUT)
202 $int = $env->set_mp_max_openfd (int maxopenfd); 289 $int = $env->set_mp_max_openfd (int maxopenfd);
203 $int = $env->set_mp_max_write (int maxwrite, int maxwrite_sleep); 290 $int = $env->set_mp_max_write (int maxwrite, int maxwrite_sleep);
204 $int = $env->set_mp_mmapsize (int mmapsize_mb) 291 $int = $env->set_mp_mmapsize (int mmapsize_mb)
205 $int = $env->set_lk_detect (U32 detect = DB_LOCK_DEFAULT) 292 $int = $env->set_lk_detect (U32 detect = DB_LOCK_DEFAULT)
206 $int = $env->set_lk_max_lockers (U32 max) 293 $int = $env->set_lk_max_lockers (U32 max)
207 $int = $env->set_lk_max_locks (U32 max) 294 $int = $env->set_lk_max_locks (U32 max)
208 $int = $env->set_lk_max_objects (U32 max) 295 $int = $env->set_lk_max_objects (U32 max)
209 $int = $env->set_lg_bsize (U32 max) 296 $int = $env->set_lg_bsize (U32 max)
210 $int = $env->set_lg_max (U32 max) 297 $int = $env->set_lg_max (U32 max)
298 $int = $env->mutex_set_increment (U32 increment)
299 $int = $env->mutex_set_tas_spins (U32 tas_spins)
300 $int = $env->mutex_set_max (U32 max)
301 $int = $env->mutex_set_align (U32 align)
211 302
212 $txn = $env->txn_begin (DB_TXN_ornull *parent = 0, U32 flags = 0) 303 $txn = $env->txn_begin (DB_TXN_ornull *parent = 0, U32 flags = 0)
213 flags: READ_COMMITTED READ_UNCOMMITTED TXN_NOSYNC TXN_NOWAIT TXN_SNAPSHOT TXN_SYNC TXN_WAIT TXN_WRITE_NOSYNC 304 flags: READ_COMMITTED READ_UNCOMMITTED TXN_NOSYNC TXN_NOWAIT TXN_SNAPSHOT TXN_SYNC TXN_WAIT TXN_WRITE_NOSYNC
214 305
215=head4 Example: 306=head4 Example:
… …
294 DESTROY (DB_TXN_ornull *txn) 385 DESTROY (DB_TXN_ornull *txn)
295 CODE: 386 CODE:
296 if (txn) 387 if (txn)
297 txn->abort (txn); 388 txn->abort (txn);
298 389
299 $int = $txn->set_timeout (NV timeout, U32 flags) 390 $int = $txn->set_timeout (NV timeout_seconds, U32 flags = SET_TXN_TIMEOUT)
300 flags: SET_LOCK_TIMEOUT SET_TXN_TIMEOUT 391 flags: SET_LOCK_TIMEOUT SET_TXN_TIMEOUT
392
393 $bool = $txn->failed
394 # see db_txn_finish documentation, above
301 395
302 396
303=head3 DBC/cursor methods 397=head3 DBC/cursor methods
304 398
305Methods available on DBC/$dbc handles: 399Methods available on DBC/$dbc handles:
306 400
307 DESTROY (DBC_ornull *dbc) 401 DESTROY (DBC_ornull *dbc)
308 CODE: 402 CODE:
309 if (dbc) 403 if (dbc)
310 dbc->c_close (dbc); 404 dbc->c_close (dbc);
405
406 $int = $cursor->set_priority ($priority = PRIORITY_*)
311 407
312=head4 Example: 408=head4 Example:
313 409
314 my $c = $db->cursor; 410 my $c = $db->cursor;
315 411
… …
349 445
350=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION 446=head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION
351 447
352=over 4 448=over 4
353 449
450=item $msg = BDB::strerror [$errno]
451
452Returns the string corresponding to the given errno value. If no argument
453is given, use C<$!>.
454
455Note that the BDB module also patches the C<$!> variable directly, so you
456should be able to get a bdb error string by simply stringifying C<$!>.
457
354=item $fileno = BDB::poll_fileno 458=item $fileno = BDB::poll_fileno
355 459
356Return the I<request result pipe file descriptor>. This filehandle must be 460Return the I<request result pipe file descriptor>. This filehandle must be
357polled for reading by some mechanism outside this module (e.g. Event or 461polled for reading by some mechanism outside this module (e.g. Event or
358select, see below or the SYNOPSIS). If the pipe becomes readable you have 462select, see below or the SYNOPSIS). If the pipe becomes readable you have
… …
396interactiveness when perl is not fast enough to process all requests in 500interactiveness when perl is not fast enough to process all requests in
397time. 501time.
398 502
399For interactive programs, values such as C<0.01> to C<0.1> should be fine. 503For interactive programs, values such as C<0.01> to C<0.1> should be fine.
400 504
401Example: Install an Event watcher that automatically calls 505Example: Install an EV watcher that automatically calls
402BDB::poll_cb with low priority, to ensure that other parts of the 506BDB::poll_cb with low priority, to ensure that other parts of the
403program get the CPU sometimes even under high AIO load. 507program get the CPU sometimes even under high load.
404 508
405 # try not to spend much more than 0.1s in poll_cb 509 # try not to spend much more than 0.1s in poll_cb
406 BDB::max_poll_time 0.1; 510 BDB::max_poll_time 0.1;
407 511
408 # use a low priority so other tasks have priority 512 my $bdb_poll = EV::io BDB::poll_fileno, EV::READ, \&BDB::poll_cb);
409 Event->io (fd => BDB::poll_fileno,
410 poll => 'r', nice => 1,
411 cb => &BDB::poll_cb);
412 513
413=item BDB::poll_wait 514=item BDB::poll_wait
414 515
415If there are any outstanding requests and none of them in the result 516If there are any outstanding requests and none of them in the result
416phase, wait till the result filehandle becomes ready for reading (simply 517phase, wait till the result filehandle becomes ready for reading (simply
… …
428 529
429 BDB::poll_wait, BDB::poll_cb 530 BDB::poll_wait, BDB::poll_cb
430 531
431=item BDB::flush 532=item BDB::flush
432 533
433Wait till all outstanding AIO requests have been handled. 534Wait till all outstanding BDB requests have been handled.
434 535
435Strictly equivalent to: 536Strictly equivalent to:
436 537
437 BDB::poll_wait, BDB::poll_cb 538 BDB::poll_wait, BDB::poll_cb
438 while BDB::nreqs; 539 while BDB::nreqs;
… …
443 544
444=over 4 545=over 4
445 546
446=item BDB::min_parallel $nthreads 547=item BDB::min_parallel $nthreads
447 548
448Set the minimum number of AIO threads to C<$nthreads>. The current 549Set the minimum number of BDB threads to C<$nthreads>. The current
449default is C<8>, which means eight asynchronous operations can execute 550default is C<8>, which means eight asynchronous operations can execute
450concurrently at any one time (the number of outstanding requests, 551concurrently at any one time (the number of outstanding requests,
451however, is unlimited). 552however, is unlimited).
452 553
453BDB starts threads only on demand, when an AIO request is queued and 554BDB starts threads only on demand, when an BDB request is queued and
454no free thread exists. Please note that queueing up a hundred requests can 555no free thread exists. Please note that queueing up a hundred requests can
455create demand for a hundred threads, even if it turns out that everything 556create demand for a hundred threads, even if it turns out that everything
456is in the cache and could have been processed faster by a single thread. 557is in the cache and could have been processed faster by a single thread.
457 558
458It is recommended to keep the number of threads relatively low, as some 559It is recommended to keep the number of threads relatively low, as some
… …
463Under most circumstances you don't need to call this function, as the 564Under most circumstances you don't need to call this function, as the
464module selects a default that is suitable for low to moderate load. 565module selects a default that is suitable for low to moderate load.
465 566
466=item BDB::max_parallel $nthreads 567=item BDB::max_parallel $nthreads
467 568
468Sets the maximum number of AIO threads to C<$nthreads>. If more than the 569Sets the maximum number of BDB threads to C<$nthreads>. If more than the
469specified number of threads are currently running, this function kills 570specified number of threads are currently running, this function kills
470them. This function blocks until the limit is reached. 571them. This function blocks until the limit is reached.
471 572
472While C<$nthreads> are zero, aio requests get queued but not executed 573While C<$nthreads> are zero, aio requests get queued but not executed
473until the number of threads has been increased again. 574until the number of threads has been increased again.
… …
512 613
513=item BDB::set_sync_prepare $cb 614=item BDB::set_sync_prepare $cb
514 615
515Sets a callback that is called whenever a request is created without an 616Sets a callback that is called whenever a request is created without an
516explicit callback. It has to return two code references. The first is used 617explicit callback. It has to return two code references. The first is used
517as the request callback, and the second is called to wait until the first 618as the request callback (it should save the return status), and the second
619is called to wait until the first callback has been called (it must set
620C<$!> to the return status).
621
622This mechanism can be used to include BDB into other event mechanisms,
623such as L<AnyEvent::BDB> or L<Coro::BDB>.
624
518callback has been called. The default implementation works like this: 625The default implementation works like this:
519 626
520 sub { 627 sub {
521 my $status; 628 my $status;
522 ( 629 (
523 sub { $status = $! }, 630 sub { $status = $! },
524 sub { BDB::poll while !defined $status; $! = $status }, 631 sub { BDB::poll while !defined $status; $! = $status },
525 ) 632 )
526 } 633 }
634
635It simply blocks the process till the request has finished and then sets
636C<$!> to the return value. This means that if you don't use a callback,
637BDB will simply fall back to synchronous operations.
527 638
528=back 639=back
529 640
530=head3 STATISTICAL INFORMATION 641=head3 STATISTICAL INFORMATION
531 642
… …
576 687
577=head2 FORK BEHAVIOUR 688=head2 FORK BEHAVIOUR
578 689
579This module should do "the right thing" when the process using it forks: 690This module should do "the right thing" when the process using it forks:
580 691
581Before the fork, IO::AIO enters a quiescent state where no requests 692Before the fork, BDB enters a quiescent state where no requests
582can be added in other threads and no results will be processed. After 693can be added in other threads and no results will be processed. After
583the fork the parent simply leaves the quiescent state and continues 694the fork the parent simply leaves the quiescent state and continues
584request/result processing, while the child frees the request/result queue 695request/result processing, while the child frees the request/result queue
585(so that the requests started before the fork will only be handled in the 696(so that the requests started before the fork will only be handled in the
586parent). Threads will be started on demand until the limit set in the 697parent). Threads will be started on demand until the limit set in the
587parent process has been reached again. 698parent process has been reached again.
588 699
589In short: the parent will, after a short pause, continue as if fork had 700In short: the parent will, after a short pause, continue as if fork had
590not been called, while the child will act as if IO::AIO has not been used 701not been called, while the child will act as if BDB has not been used
591yet. 702yet.
703
704Win32 note: there is no fork on win32, and perls emulation of it is too
705broken to be supported, so do not use BDB in a windows pseudo-fork, better
706yet, switch to a more capable platform.
592 707
593=head2 MEMORY USAGE 708=head2 MEMORY USAGE
594 709
595Per-request usage: 710Per-request usage:
596 711
… …
609temporary buffers, and each thread requires a stack and other data 724temporary buffers, and each thread requires a stack and other data
610structures (usually around 16k-128k, depending on the OS). 725structures (usually around 16k-128k, depending on the OS).
611 726
612=head1 KNOWN BUGS 727=head1 KNOWN BUGS
613 728
614Known bugs will be fixed in the next release. 729Known bugs will be fixed in the next release, except:
730
731 If you use a transaction in any request, and the request returns
732 with an operating system error or DB_LOCK_NOTGRANTED, the internal
733 TXN_DEADLOCK flag will be set on the transaction. See C<db_txn_finish>,
734 above.
615 735
616=head1 SEE ALSO 736=head1 SEE ALSO
617 737
618L<Coro::AIO>. 738L<AnyEvent::BDB> (event loop integration), L<Coro::BDB> (more natural
739syntax), L<IO::AIO> (nice to have).
619 740
620=head1 AUTHOR 741=head1 AUTHOR
621 742
622 Marc Lehmann <schmorp@schmorp.de> 743 Marc Lehmann <schmorp@schmorp.de>
623 http://home.schmorp.de/ 744 http://home.schmorp.de/

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