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
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 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.).

For very fast queries ("select 0"), this module can add noticable overhead
(around 15%) as it tries to switch to other coroutines when mysqld doesn't
deliver the data instantly.

For most types of queries, there will be no overhead, 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 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 Coro::Handle ();

# 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.

=cut

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

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

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

      $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 $dbh = Coro::Mysql::unblock DBI->connect ($database, $user, $pass)
         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:	1.6
Committed:	Wed Sep 1 16:38:07 2010 UTC (13 years, 8 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_02
Changes since 1.5:	+1 -1 lines
Log Message:	1.02
#	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
26	F<libmysqlclient> library as DBD::mysql, otherwise it will not work.
27
28	Also, while this module makes database handles non-blocking, you still
29	cannot run multiple requests in parallel on the same database handle. If
30	you want to run multiple queries in parallel, you have to create multiple
31	database connections, one for each thread that runs queries. Not doing so
32	can corrupt your data - use a Coro::Semaphore when in doubt.
33
34	If you make sure that you never run two or more requests in parallel, you
35	can freely share the database handles between threads, of course.
36
37	Also, this module uses a number of "unclean" techniques (patching an
38	internal libmysql structure for one thing) and was hacked within a few
39	hours on a long flight to Malaysia.
40
41	It does, however, check whether it indeed got the structure layout
42	correct, so you should expect perl exceptions or early crashes as opposed
43	to data corruption when something goes wrong during patching.
44
45	=head2 SPEED
46
47	This module is implemented in XS, and as long as mysqld replies quickly
48	enough, it adds no overhead to the standard libmysql communication
49	routines (which are very badly written, btw.).
50
51	For very fast queries ("select 0"), this module can add noticable overhead
52	(around 15%) as it tries to switch to other coroutines when mysqld doesn't
53	deliver the data instantly.
54
55	For most types of queries, there will be no overhead, especially on
56	multicore systems where your perl process can do other things while mysqld
57	does its stuff.
58
59	=head2 LIMITATIONS
60
61	This module only supports "standard" mysql connection handles - this
62	means unix domain or TCP sockets, and excludes SSL/TLS connections, named
63	pipes (windows) and shared memory (also windows). No support for these
64	connection types is planned, either.
65
66	=head1 FUNCTIONS
67
68	Coro::Mysql offers a single user-accessible function:
69
70	=over 4
71
72	=cut
73
74	package Coro::Mysql;
75
76	use strict qw(vars subs);
77	no warnings;
78
79	use Scalar::Util ();
80	use Carp qw(croak);
81
82	use Guard;
83	use Coro::Handle ();
84
85	# we need this extra indirection, as Coro doesn't support
86	# calling SLF-like functions via call_sv.
87
88	sub readable { &Coro::Handle::FH::readable }
89	sub writable { &Coro::Handle::FH::writable }
90
91	BEGIN {
92	our $VERSION = '1.02';
93
94	require XSLoader;
95	XSLoader::load Coro::Mysql::, $VERSION;
96	}
97
98	=item $DBH = Coro::Mysql::unblock $DBH
99
100	This function takes a DBI database handles and "patches" it
101	so it becomes compatible to Coro threads.
102
103	After that, it returns the patched handle - you should always use the
104	newly returned database handle.
105
106	It is safe to call this function on any database handle (or just about any
107	value), but it will only do anything to L<DBD::mysql> handles, others are
108	returned unchanged. That means it is harmless when applied to database
109	handles of other databases.
110
111	=cut
112
113	sub unblock {
114	my ($DBH) = @_;
115
116	if ($DBH->{Driver}{Name} eq "mysql") {
117	my $sock = $DBH->{sock};
118
119	open my $fh, "+>&" . $DBH->{sockfd}
120	or croak "Coro::Mysql unable to clone mysql fd";
121
122	$fh = Coro::Handle::unblock $fh;
123
124	_patch $sock, $DBH->{sockfd}, $fh, tied ${$fh};
125	}
126
127	$DBH
128	}
129
130	1;
131
132	=back
133
134	=head1 USAGE EXAMPLE
135
136	This example uses L<PApp::SQL> and L<Coro::on_enter> to implement a
137	function C<with_db>, that connects to a database, uses C<unblock> on the
138	resulting handle and then makes sure that C<$PApp::SQL::DBH> is set to the
139	(per-thread) database handle when the given thread is running (it does not
140	restore any previous value of $PApp::SQL::DBH, however):
141
142	use Coro;
143	use Coro::Mysql;
144	use PApp::SQL;
145
146	sub with_db($$$&) {
147	my ($database, $user, $pass, $cb) = @_;
148
149	my $dbh = Coro::Mysql::unblock DBI->connect ($database, $user, $pass)
150	or die $DBI::errstr;
151
152	Coro::on_enter { $PApp::SQL::DBH = $dbh };
153
154	$cb->();
155	}
156
157	This function makes it possible to easily use L<PApp::SQL> with
158	L<Coro::Mysql>, without worrying about database handles.
159
160	# now start 10 threads doing stuff
161	async {
162
163	with_db "DBI:mysql:test", "", "", sub {
164	sql_exec "update table set col = 5 where id = 7";
165
166	my $st = sql_exec \my ($id, $name),
167	"select id, name from table where name like ?",
168	"a%";
169
170	while ($st->fetch) {
171	...
172	}
173
174	my $id = sql_insertid sql_exec "insert into table values (1,2,3)";
175	# etc.
176	};
177
178	} for 1..10;
179
180	=head1 SEE ALSO
181
182	L<Coro>, L<PApp::SQL> (a user friendly but efficient wrapper around DBI).
183
184	=head1 AUTHOR
185
186	Marc Lehmann <schmorp@schmorp.de>
187	http://home.schmorp.de/
188
189	=cut
190