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3 | BDB - Asynchronous Berkeley DB access |
3 | BDB - Asynchronous Berkeley DB access |
4 | |
4 | |
5 | =head1 SYNOPSIS |
5 | =head1 SYNOPSIS |
6 | |
6 | |
7 | use BDB; |
7 | use BDB; |
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8 | |
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9 | my $env = db_env_create; |
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10 | |
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11 | mkdir "bdtest", 0700; |
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12 | db_env_open |
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13 | $env, |
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14 | "bdtest", |
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15 | BDB::INIT_LOCK | BDB::INIT_LOG | BDB::INIT_MPOOL |
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16 | | BDB::INIT_TXN | BDB::RECOVER | BDB::USE_ENVIRON | BDB::CREATE, |
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17 | 0600; |
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18 | |
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19 | $env->set_flags (BDB::AUTO_COMMIT | BDB::TXN_NOSYNC, 1); |
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20 | |
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21 | my $db = db_create $env; |
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22 | db_open $db, undef, "table", undef, BDB::BTREE, BDB::AUTO_COMMIT | BDB::CREATE |
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23 | | BDB::READ_UNCOMMITTED, 0600; |
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24 | db_put $db, undef, "key", "data", 0, sub { |
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25 | db_del $db, undef, "key"; |
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26 | }; |
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27 | db_sync $db; |
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28 | |
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29 | # when you also use Coro, management is easy: |
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30 | use Coro::BDB; |
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31 | |
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32 | # automatic event loop intergration with AnyEvent: |
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33 | use AnyEvent::BDB; |
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34 | |
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35 | # automatic result processing with EV: |
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36 | my $WATCHER = EV::io BDB::poll_fileno, EV::READ, \&BDB::poll_cb; |
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37 | |
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38 | # with Glib: |
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39 | add_watch Glib::IO BDB::poll_fileno, |
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40 | in => sub { BDB::poll_cb; 1 }; |
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41 | |
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42 | # or simply flush manually |
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43 | BDB::flush; |
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44 | |
8 | |
45 | |
9 | =head1 DESCRIPTION |
46 | =head1 DESCRIPTION |
10 | |
47 | |
11 | See the BerkeleyDB documentation (L<http://www.oracle.com/technology/documentation/berkeley-db/db/index.html>). |
48 | 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). |
49 | The BDB API is very similar to the C API (the translation has been very faithful). |
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72 | use strict 'vars'; |
109 | use strict 'vars'; |
73 | |
110 | |
74 | use base 'Exporter'; |
111 | use base 'Exporter'; |
75 | |
112 | |
76 | BEGIN { |
113 | BEGIN { |
77 | our $VERSION = '1.1'; |
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 |
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 |
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120 | db_put db_get db_pget db_del db_key_range |
83 | db_txn_commit db_txn_abort db_txn_finish |
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 | ); |
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95 | |
133 | |
96 | require XSLoader; |
134 | require XSLoader; |
97 | XSLoader::load ("BDB", $VERSION); |
135 | XSLoader::load ("BDB", $VERSION); |
98 | } |
136 | } |
99 | |
137 | |
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138 | =head2 WIN32 FILENAMES/DATABASE NAME MESS |
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139 | |
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140 | Perl on Win32 supports only ASCII filenames (the reason is that it abuses |
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141 | an internal flag to store wether a filename is Unicode or ANSI, but that |
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142 | flag is used for somethign else in the perl core, so there is no way to |
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143 | detect wether a filename is ANSI or Unicode-encoded). The BDB module |
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144 | tries to work around this issue by assuming that the filename is an ANSI |
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145 | filename and BDB was built for unicode support. |
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146 | |
100 | =head2 BERKELEYDB FUNCTIONS |
147 | =head2 BERKELEYDB FUNCTIONS |
101 | |
148 | |
102 | All of these are functions. The create functions simply return a new |
149 | All of these are functions. The create functions simply return a new |
103 | object and never block. All the remaining functions all take an optional |
150 | object and never block. All the remaining functions take an optional |
104 | callback as last argument. If it is missing, then the fucntion will be |
151 | callback as last argument. If it is missing, then the function will be |
105 | executed synchronously. |
152 | executed synchronously. In both cases, C<$!> will reflect the return value |
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153 | of the function. |
106 | |
154 | |
107 | BDB functions that cannot block (mostly functions that manipulate |
155 | BDB functions that cannot block (mostly functions that manipulate |
108 | settings) are method calls on the relevant objects, so the rule of thumb |
156 | 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 |
157 | is: if it's a method, it's not blocking, if it's a function, it takes a |
110 | callback as last argument. |
158 | callback as last argument. |
111 | |
159 | |
112 | In the following, C<$int> signifies an integer return value, |
160 | In the following, C<$int> signifies an integer return value, |
113 | C<octetstring> is a "binary string" (i.e. a perl string with no character |
161 | 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 |
162 | indices >255), C<U32> is an unsigned 32 bit integer, C<int> is some |
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145 | |
193 | |
146 | db_open (DB *db, DB_TXN_ornull *txnid, octetstring file, octetstring database, int type, U32 flags, int mode, SV *callback = &PL_sv_undef) |
194 | 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 |
195 | 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) |
196 | db_close (DB *db, U32 flags = 0, SV *callback = &PL_sv_undef) |
149 | flags: DB_NOSYNC |
197 | flags: DB_NOSYNC |
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198 | db_upgrade (DB *db, octetstring 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) |
199 | 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 |
200 | flags: FREELIST_ONLY FREE_SPACE |
152 | db_sync (DB *db, U32 flags = 0, SV *callback = &PL_sv_undef) |
201 | 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) |
202 | 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) |
203 | db_put (DB *db, DB_TXN_ornull *txn, SV *key, SV *data, U32 flags = 0, SV *callback = &PL_sv_undef) |
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242 | $int = $env->set_lk_max_lockers (U32 max) |
291 | $int = $env->set_lk_max_lockers (U32 max) |
243 | $int = $env->set_lk_max_locks (U32 max) |
292 | $int = $env->set_lk_max_locks (U32 max) |
244 | $int = $env->set_lk_max_objects (U32 max) |
293 | $int = $env->set_lk_max_objects (U32 max) |
245 | $int = $env->set_lg_bsize (U32 max) |
294 | $int = $env->set_lg_bsize (U32 max) |
246 | $int = $env->set_lg_max (U32 max) |
295 | $int = $env->set_lg_max (U32 max) |
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296 | $int = $env->mutex_set_increment (U32 increment) |
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297 | $int = $env->mutex_set_tas_spins (U32 tas_spins) |
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298 | $int = $env->mutex_set_max (U32 max) |
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299 | $int = $env->mutex_set_align (U32 align) |
247 | |
300 | |
248 | $txn = $env->txn_begin (DB_TXN_ornull *parent = 0, U32 flags = 0) |
301 | $txn = $env->txn_begin (DB_TXN_ornull *parent = 0, U32 flags = 0) |
249 | flags: READ_COMMITTED READ_UNCOMMITTED TXN_NOSYNC TXN_NOWAIT TXN_SNAPSHOT TXN_SYNC TXN_WAIT TXN_WRITE_NOSYNC |
302 | flags: READ_COMMITTED READ_UNCOMMITTED TXN_NOSYNC TXN_NOWAIT TXN_SNAPSHOT TXN_SYNC TXN_WAIT TXN_WRITE_NOSYNC |
250 | |
303 | |
251 | =head4 Example: |
304 | =head4 Example: |
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346 | DESTROY (DBC_ornull *dbc) |
399 | DESTROY (DBC_ornull *dbc) |
347 | CODE: |
400 | CODE: |
348 | if (dbc) |
401 | if (dbc) |
349 | dbc->c_close (dbc); |
402 | dbc->c_close (dbc); |
350 | |
403 | |
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404 | $int = $cursor->set_priority ($priority = PRIORITY_*) |
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405 | |
351 | =head4 Example: |
406 | =head4 Example: |
352 | |
407 | |
353 | my $c = $db->cursor; |
408 | my $c = $db->cursor; |
354 | |
409 | |
355 | for (;;) { |
410 | for (;;) { |
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388 | |
443 | |
389 | =head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION |
444 | =head3 EVENT PROCESSING AND EVENT LOOP INTEGRATION |
390 | |
445 | |
391 | =over 4 |
446 | =over 4 |
392 | |
447 | |
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448 | =item $msg = BDB::strerror [$errno] |
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449 | |
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450 | Returns the string corresponding to the given errno value. If no argument |
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451 | is given, use C<$!>. |
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452 | |
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453 | Note that the BDB module also patches the C<$!> variable directly, so you |
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454 | should be able to get a bdb error string by simply stringifying C<$!>. |
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455 | |
393 | =item $fileno = BDB::poll_fileno |
456 | =item $fileno = BDB::poll_fileno |
394 | |
457 | |
395 | Return the I<request result pipe file descriptor>. This filehandle must be |
458 | Return the I<request result pipe file descriptor>. This filehandle must be |
396 | polled for reading by some mechanism outside this module (e.g. Event or |
459 | polled for reading by some mechanism outside this module (e.g. Event or |
397 | select, see below or the SYNOPSIS). If the pipe becomes readable you have |
460 | select, see below or the SYNOPSIS). If the pipe becomes readable you have |
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435 | interactiveness when perl is not fast enough to process all requests in |
498 | interactiveness when perl is not fast enough to process all requests in |
436 | time. |
499 | time. |
437 | |
500 | |
438 | For interactive programs, values such as C<0.01> to C<0.1> should be fine. |
501 | For interactive programs, values such as C<0.01> to C<0.1> should be fine. |
439 | |
502 | |
440 | Example: Install an Event watcher that automatically calls |
503 | Example: Install an EV watcher that automatically calls |
441 | BDB::poll_cb with low priority, to ensure that other parts of the |
504 | BDB::poll_cb with low priority, to ensure that other parts of the |
442 | program get the CPU sometimes even under high AIO load. |
505 | program get the CPU sometimes even under high load. |
443 | |
506 | |
444 | # try not to spend much more than 0.1s in poll_cb |
507 | # try not to spend much more than 0.1s in poll_cb |
445 | BDB::max_poll_time 0.1; |
508 | BDB::max_poll_time 0.1; |
446 | |
509 | |
447 | # use a low priority so other tasks have priority |
510 | my $bdb_poll = EV::io BDB::poll_fileno, EV::READ, \&BDB::poll_cb); |
448 | Event->io (fd => BDB::poll_fileno, |
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449 | poll => 'r', nice => 1, |
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450 | cb => &BDB::poll_cb); |
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451 | |
511 | |
452 | =item BDB::poll_wait |
512 | =item BDB::poll_wait |
453 | |
513 | |
454 | If there are any outstanding requests and none of them in the result |
514 | If there are any outstanding requests and none of them in the result |
455 | phase, wait till the result filehandle becomes ready for reading (simply |
515 | phase, wait till the result filehandle becomes ready for reading (simply |
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467 | |
527 | |
468 | BDB::poll_wait, BDB::poll_cb |
528 | BDB::poll_wait, BDB::poll_cb |
469 | |
529 | |
470 | =item BDB::flush |
530 | =item BDB::flush |
471 | |
531 | |
472 | Wait till all outstanding AIO requests have been handled. |
532 | Wait till all outstanding BDB requests have been handled. |
473 | |
533 | |
474 | Strictly equivalent to: |
534 | Strictly equivalent to: |
475 | |
535 | |
476 | BDB::poll_wait, BDB::poll_cb |
536 | BDB::poll_wait, BDB::poll_cb |
477 | while BDB::nreqs; |
537 | while BDB::nreqs; |
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482 | |
542 | |
483 | =over 4 |
543 | =over 4 |
484 | |
544 | |
485 | =item BDB::min_parallel $nthreads |
545 | =item BDB::min_parallel $nthreads |
486 | |
546 | |
487 | Set the minimum number of AIO threads to C<$nthreads>. The current |
547 | Set the minimum number of BDB threads to C<$nthreads>. The current |
488 | default is C<8>, which means eight asynchronous operations can execute |
548 | default is C<8>, which means eight asynchronous operations can execute |
489 | concurrently at any one time (the number of outstanding requests, |
549 | concurrently at any one time (the number of outstanding requests, |
490 | however, is unlimited). |
550 | however, is unlimited). |
491 | |
551 | |
492 | BDB starts threads only on demand, when an AIO request is queued and |
552 | BDB starts threads only on demand, when an BDB request is queued and |
493 | no free thread exists. Please note that queueing up a hundred requests can |
553 | no free thread exists. Please note that queueing up a hundred requests can |
494 | create demand for a hundred threads, even if it turns out that everything |
554 | create demand for a hundred threads, even if it turns out that everything |
495 | is in the cache and could have been processed faster by a single thread. |
555 | is in the cache and could have been processed faster by a single thread. |
496 | |
556 | |
497 | It is recommended to keep the number of threads relatively low, as some |
557 | It is recommended to keep the number of threads relatively low, as some |
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502 | Under most circumstances you don't need to call this function, as the |
562 | Under most circumstances you don't need to call this function, as the |
503 | module selects a default that is suitable for low to moderate load. |
563 | module selects a default that is suitable for low to moderate load. |
504 | |
564 | |
505 | =item BDB::max_parallel $nthreads |
565 | =item BDB::max_parallel $nthreads |
506 | |
566 | |
507 | Sets the maximum number of AIO threads to C<$nthreads>. If more than the |
567 | Sets the maximum number of BDB threads to C<$nthreads>. If more than the |
508 | specified number of threads are currently running, this function kills |
568 | specified number of threads are currently running, this function kills |
509 | them. This function blocks until the limit is reached. |
569 | them. This function blocks until the limit is reached. |
510 | |
570 | |
511 | While C<$nthreads> are zero, aio requests get queued but not executed |
571 | While C<$nthreads> are zero, aio requests get queued but not executed |
512 | until the number of threads has been increased again. |
572 | until the number of threads has been increased again. |
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551 | |
611 | |
552 | =item BDB::set_sync_prepare $cb |
612 | =item BDB::set_sync_prepare $cb |
553 | |
613 | |
554 | Sets a callback that is called whenever a request is created without an |
614 | Sets a callback that is called whenever a request is created without an |
555 | explicit callback. It has to return two code references. The first is used |
615 | explicit callback. It has to return two code references. The first is used |
556 | as the request callback, and the second is called to wait until the first |
616 | as the request callback (it should save the return status), and the second |
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617 | is called to wait until the first callback has been called (it must set |
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618 | C<$!> to the return status). |
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619 | |
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620 | This mechanism can be used to include BDB into other event mechanisms, |
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621 | such as L<AnyEvent::BDB> or L<Coro::BDB>. |
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622 | |
557 | callback has been called. The default implementation works like this: |
623 | The default implementation works like this: |
558 | |
624 | |
559 | sub { |
625 | sub { |
560 | my $status; |
626 | my $status; |
561 | ( |
627 | ( |
562 | sub { $status = $! }, |
628 | sub { $status = $! }, |
563 | sub { BDB::poll while !defined $status; $! = $status }, |
629 | sub { BDB::poll while !defined $status; $! = $status }, |
564 | ) |
630 | ) |
565 | } |
631 | } |
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632 | |
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633 | It simply blocks the process till the request has finished and then sets |
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634 | C<$!> to the return value. This means that if you don't use a callback, |
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635 | BDB will simply fall back to synchronous operations. |
566 | |
636 | |
567 | =back |
637 | =back |
568 | |
638 | |
569 | =head3 STATISTICAL INFORMATION |
639 | =head3 STATISTICAL INFORMATION |
570 | |
640 | |
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615 | |
685 | |
616 | =head2 FORK BEHAVIOUR |
686 | =head2 FORK BEHAVIOUR |
617 | |
687 | |
618 | This module should do "the right thing" when the process using it forks: |
688 | This module should do "the right thing" when the process using it forks: |
619 | |
689 | |
620 | Before the fork, IO::AIO enters a quiescent state where no requests |
690 | Before the fork, BDB enters a quiescent state where no requests |
621 | can be added in other threads and no results will be processed. After |
691 | can be added in other threads and no results will be processed. After |
622 | the fork the parent simply leaves the quiescent state and continues |
692 | the fork the parent simply leaves the quiescent state and continues |
623 | request/result processing, while the child frees the request/result queue |
693 | request/result processing, while the child frees the request/result queue |
624 | (so that the requests started before the fork will only be handled in the |
694 | (so that the requests started before the fork will only be handled in the |
625 | parent). Threads will be started on demand until the limit set in the |
695 | parent). Threads will be started on demand until the limit set in the |
626 | parent process has been reached again. |
696 | parent process has been reached again. |
627 | |
697 | |
628 | In short: the parent will, after a short pause, continue as if fork had |
698 | In short: the parent will, after a short pause, continue as if fork had |
629 | not been called, while the child will act as if IO::AIO has not been used |
699 | not been called, while the child will act as if BDB has not been used |
630 | yet. |
700 | yet. |
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701 | |
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702 | Win32 note: there is no fork on win32, and perls emulation of it is too |
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703 | broken to be supported, so do not use BDB in a windows pseudo-fork, better |
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704 | yet, switch to a more capable platform. |
631 | |
705 | |
632 | =head2 MEMORY USAGE |
706 | =head2 MEMORY USAGE |
633 | |
707 | |
634 | Per-request usage: |
708 | Per-request usage: |
635 | |
709 | |
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657 | TXN_DEADLOCK flag will be set on the transaction. See C<db_txn_finish>, |
731 | TXN_DEADLOCK flag will be set on the transaction. See C<db_txn_finish>, |
658 | above. |
732 | above. |
659 | |
733 | |
660 | =head1 SEE ALSO |
734 | =head1 SEE ALSO |
661 | |
735 | |
662 | L<Coro::AIO>. |
736 | L<AnyEvent::BDB> (event loop integration), L<Coro::BDB> (more natural |
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737 | syntax), L<IO::AIO> (nice to have). |
663 | |
738 | |
664 | =head1 AUTHOR |
739 | =head1 AUTHOR |
665 | |
740 | |
666 | Marc Lehmann <schmorp@schmorp.de> |
741 | Marc Lehmann <schmorp@schmorp.de> |
667 | http://home.schmorp.de/ |
742 | http://home.schmorp.de/ |