Coro-Mysql/Mysql.pm

=head1 NAME

Coro::Mysql - let other threads run while doing mysql requests

=head1 SYNOPSIS

 use Coro::Mysql;

 my $DBH = Coro::Mysql::unblock DBI->connect (...);

=head1 DESCRIPTION

(Note that in this manual, "thread" refers to real threads as implemented
by the Coro module, not to the built-in windows process emulation which
unfortunately is also called "threads")

This module "patches" DBD::mysql database handles so that they do not
block the whole process, but only the thread that they are used in.

This can be used to make parallel sql requests using Coro, or to do other
stuff while mysql is rumbling in the background.

=head2 CAVEAT

Note that this module must be linked against exactly the same (shared,
possibly not working with all OSes) F<libmysqlclient> library as
DBD::mysql, otherwise it will not work.

Also, while this module makes database handles non-blocking, you still
cannot run multiple requests in parallel on the same database handle. If
you want to run multiple queries in parallel, you have to create multiple
database connections, one for each thread that runs queries. Not doing so
can corrupt your data - use a Coro::Semaphore when in doubt.

If you make sure that you never run two or more requests in parallel, you
can freely share the database handles between threads, of course.

Also, this module uses a number of "unclean" techniques (patching an
internal libmysql structure for one thing) and was initially hacked within
a few hours on a long flight to Malaysia.

It does, however, check whether it indeed got the structure layout
correct, so you should expect perl exceptions or early crashes as opposed
to data corruption when something goes wrong during patching.

=head2 SPEED

This module is implemented in XS, and as long as mysqld replies quickly
enough, it adds no overhead to the standard libmysql communication
routines (which are very badly written, btw.). In fact, since it has a
more efficient buffering and allows requests to run in parallel, it often
decreases the actual time to run many queries considerably.

For very fast queries ("select 0"), this module can add noticable overhead
(around 15%, 7% when EV can be used) as it tries to switch to other
coroutines when mysqld doesn't deliver the data immediately, although,
again, when running queries in parallel, they will usually execute faster.

For most types of queries, there will be no extra latency, especially on
multicore systems where your perl process can do other things while mysqld
does its stuff.

=head2 LIMITATIONS

This module only supports "standard" mysql connection handles - this
means unix domain or TCP sockets, and excludes SSL/TLS connections, named
pipes (windows) and shared memory (also windows). No support for these
connection types is planned, either.

=head1 CANCELLATION

Cancelling a thread that is within a mysql query will likely make the
handle unusable. As far as Coro::Mysql is concerned, the handle can be
safely destroyed, but it's not clear how mysql itself will react to a
cancellation.

=head1 FUNCTIONS

Coro::Mysql offers a single user-accessible function:

=over 4

=cut

package Coro::Mysql;

use strict qw(vars subs);
no warnings;

use Scalar::Util ();
use Carp qw(croak);

use Guard;
use AnyEvent ();
use Coro ();
use Coro::AnyEvent (); # not necessary with newer Coro versions

# we need this extra indirection, as Coro doesn't support
# calling SLF-like functions via call_sv.

sub readable { &Coro::Handle::FH::readable }
sub writable { &Coro::Handle::FH::writable }

BEGIN {
   our $VERSION = '1.02';

   require XSLoader;
   XSLoader::load Coro::Mysql::, $VERSION;
}

=item $DBH = Coro::Mysql::unblock $DBH

This function takes a DBI database handles and "patches" it
so it becomes compatible to Coro threads.

After that, it returns the patched handle - you should always use the
newly returned database handle.

It is safe to call this function on any database handle (or just about any
value), but it will only do anything to L<DBD::mysql> handles, others are
returned unchanged. That means it is harmless when applied to database
handles of other databases.

It is also safe to pass C<undef>, so code like this is works as expected:

   my $dbh = DBI->connect ($database, $user, $pass)->Coro::Mysql::unblock
      or die $DBI::errstr;

=cut

sub unblock {
   my ($DBH) = @_;

   if ($DBH && $DBH->{Driver}{Name} eq "mysql") {
      my $sock = $DBH->{sock};

      open my $fh, "+>&" . $DBH->{sockfd}
         or croak "Coro::Mysql unable to clone mysql fd";

      if (AnyEvent::detect ne "AnyEvent::Impl::EV" || !_use_ev) {
         require Coro::Handle;
         $fh = Coro::Handle::unblock ($fh);
      }

      _patch $sock, $DBH->{sockfd}, $fh, tied ${$fh};
   }

   $DBH
}

1;

=back

=head1 USAGE EXAMPLE

This example uses L<PApp::SQL> and L<Coro::on_enter> to implement a
function C<with_db>, that connects to a database, uses C<unblock> on the
resulting handle and then makes sure that C<$PApp::SQL::DBH> is set to the
(per-thread) database handle when the given thread is running (it does not
restore any previous value of $PApp::SQL::DBH, however):

   use Coro;
   use Coro::Mysql;
   use PApp::SQL;

   sub with_db($$$&) {
      my ($database, $user, $pass, $cb) = @_;

      my $dbh = DBI->connect ($database, $user, $pass)->Coro::Mysql::unblock
         or die $DBI::errstr;

      Coro::on_enter { $PApp::SQL::DBH = $dbh };

      $cb->();
   }  

This function makes it possible to easily use L<PApp::SQL> with
L<Coro::Mysql>, without worrying about database handles.

   # now start 10 threads doing stuff
   async {

      with_db "DBI:mysql:test", "", "", sub {
         sql_exec "update table set col = 5 where id = 7";

         my $st = sql_exec \my ($id, $name),
                           "select id, name from table where name like ?",
                           "a%";

         while ($st->fetch) {
            ...
         }

         my $id = sql_insertid sql_exec "insert into table values (1,2,3)";
         # etc.
      };

   } for 1..10;

=head1 SEE ALSO

L<Coro>, L<PApp::SQL> (a user friendly but efficient wrapper around DBI).

=head1 AUTHOR

 Marc Lehmann <schmorp@schmorp.de>
 http://home.schmorp.de/

=cut

Revision:	1.10
Committed:	Thu Feb 17 02:06:55 2011 UTC (13 years, 3 months ago) by root
Branch:	MAIN
Changes since 1.9:	+6 -1 lines
Log Message:	* empty log message *
#	Content
1	=head1 NAME
2
3	Coro::Mysql - let other threads run while doing mysql requests
4
5	=head1 SYNOPSIS
6
7	use Coro::Mysql;
8
9	my $DBH = Coro::Mysql::unblock DBI->connect (...);
10
11	=head1 DESCRIPTION
12
13	(Note that in this manual, "thread" refers to real threads as implemented
14	by the Coro module, not to the built-in windows process emulation which
15	unfortunately is also called "threads")
16
17	This module "patches" DBD::mysql database handles so that they do not
18	block the whole process, but only the thread that they are used in.
19
20	This can be used to make parallel sql requests using Coro, or to do other
21	stuff while mysql is rumbling in the background.
22
23	=head2 CAVEAT
24
25	Note that this module must be linked against exactly the same (shared,
26	possibly not working with all OSes) F<libmysqlclient> library as
27	DBD::mysql, otherwise it will not work.
28
29	Also, while this module makes database handles non-blocking, you still
30	cannot run multiple requests in parallel on the same database handle. If
31	you want to run multiple queries in parallel, you have to create multiple
32	database connections, one for each thread that runs queries. Not doing so
33	can corrupt your data - use a Coro::Semaphore when in doubt.
34
35	If you make sure that you never run two or more requests in parallel, you
36	can freely share the database handles between threads, of course.
37
38	Also, this module uses a number of "unclean" techniques (patching an
39	internal libmysql structure for one thing) and was initially hacked within
40	a few hours on a long flight to Malaysia.
41
42	It does, however, check whether it indeed got the structure layout
43	correct, so you should expect perl exceptions or early crashes as opposed
44	to data corruption when something goes wrong during patching.
45
46	=head2 SPEED
47
48	This module is implemented in XS, and as long as mysqld replies quickly
49	enough, it adds no overhead to the standard libmysql communication
50	routines (which are very badly written, btw.). In fact, since it has a
51	more efficient buffering and allows requests to run in parallel, it often
52	decreases the actual time to run many queries considerably.
53
54	For very fast queries ("select 0"), this module can add noticable overhead
55	(around 15%, 7% when EV can be used) as it tries to switch to other
56	coroutines when mysqld doesn't deliver the data immediately, although,
57	again, when running queries in parallel, they will usually execute faster.
58
59	For most types of queries, there will be no extra latency, especially on
60	multicore systems where your perl process can do other things while mysqld
61	does its stuff.
62
63	=head2 LIMITATIONS
64
65	This module only supports "standard" mysql connection handles - this
66	means unix domain or TCP sockets, and excludes SSL/TLS connections, named
67	pipes (windows) and shared memory (also windows). No support for these
68	connection types is planned, either.
69
70	=head1 CANCELLATION
71
72	Cancelling a thread that is within a mysql query will likely make the
73	handle unusable. As far as Coro::Mysql is concerned, the handle can be
74	safely destroyed, but it's not clear how mysql itself will react to a
75	cancellation.
76
77	=head1 FUNCTIONS
78
79	Coro::Mysql offers a single user-accessible function:
80
81	=over 4
82
83	=cut
84
85	package Coro::Mysql;
86
87	use strict qw(vars subs);
88	no warnings;
89
90	use Scalar::Util ();
91	use Carp qw(croak);
92
93	use Guard;
94	use AnyEvent ();
95	use Coro ();
96	use Coro::AnyEvent (); # not necessary with newer Coro versions
97
98	# we need this extra indirection, as Coro doesn't support
99	# calling SLF-like functions via call_sv.
100
101	sub readable { &Coro::Handle::FH::readable }
102	sub writable { &Coro::Handle::FH::writable }
103
104	BEGIN {
105	our $VERSION = '1.02';
106
107	require XSLoader;
108	XSLoader::load Coro::Mysql::, $VERSION;
109	}
110
111	=item $DBH = Coro::Mysql::unblock $DBH
112
113	This function takes a DBI database handles and "patches" it
114	so it becomes compatible to Coro threads.
115
116	After that, it returns the patched handle - you should always use the
117	newly returned database handle.
118
119	It is safe to call this function on any database handle (or just about any
120	value), but it will only do anything to L<DBD::mysql> handles, others are
121	returned unchanged. That means it is harmless when applied to database
122	handles of other databases.
123
124	It is also safe to pass C<undef>, so code like this is works as expected:
125
126	my $dbh = DBI->connect ($database, $user, $pass)->Coro::Mysql::unblock
127	or die $DBI::errstr;
128
129	=cut
130
131	sub unblock {
132	my ($DBH) = @_;
133
134	if ($DBH && $DBH->{Driver}{Name} eq "mysql") {
135	my $sock = $DBH->{sock};
136
137	open my $fh, "+>&" . $DBH->{sockfd}
138	or croak "Coro::Mysql unable to clone mysql fd";
139
140	if (AnyEvent::detect ne "AnyEvent::Impl::EV" \|\| !_use_ev) {
141	require Coro::Handle;
142	$fh = Coro::Handle::unblock ($fh);
143	}
144
145	_patch $sock, $DBH->{sockfd}, $fh, tied ${$fh};
146	}
147
148	$DBH
149	}
150
151	1;
152
153	=back
154
155	=head1 USAGE EXAMPLE
156
157	This example uses L<PApp::SQL> and L<Coro::on_enter> to implement a
158	function C<with_db>, that connects to a database, uses C<unblock> on the
159	resulting handle and then makes sure that C<$PApp::SQL::DBH> is set to the
160	(per-thread) database handle when the given thread is running (it does not
161	restore any previous value of $PApp::SQL::DBH, however):
162
163	use Coro;
164	use Coro::Mysql;
165	use PApp::SQL;
166
167	sub with_db($$$&) {
168	my ($database, $user, $pass, $cb) = @_;
169
170	my $dbh = DBI->connect ($database, $user, $pass)->Coro::Mysql::unblock
171	or die $DBI::errstr;
172
173	Coro::on_enter { $PApp::SQL::DBH = $dbh };
174
175	$cb->();
176	}
177
178	This function makes it possible to easily use L<PApp::SQL> with
179	L<Coro::Mysql>, without worrying about database handles.
180
181	# now start 10 threads doing stuff
182	async {
183
184	with_db "DBI:mysql:test", "", "", sub {
185	sql_exec "update table set col = 5 where id = 7";
186
187	my $st = sql_exec \my ($id, $name),
188	"select id, name from table where name like ?",
189	"a%";
190
191	while ($st->fetch) {
192	...
193	}
194
195	my $id = sql_insertid sql_exec "insert into table values (1,2,3)";
196	# etc.
197	};
198
199	} for 1..10;
200
201	=head1 SEE ALSO
202
203	L<Coro>, L<PApp::SQL> (a user friendly but efficient wrapper around DBI).
204
205	=head1 AUTHOR
206
207	Marc Lehmann <schmorp@schmorp.de>
208	http://home.schmorp.de/
209
210	=cut
211