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 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:	1.7
Committed:	Thu Jan 13 11:57:09 2011 UTC (13 years, 5 months ago) by root
Branch:	MAIN
Changes since 1.6:	+3 -2 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 hacked within a few
40	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.).
51
52	For very fast queries ("select 0"), this module can add noticable overhead
53	(around 15%) as it tries to switch to other coroutines when mysqld doesn't
54	deliver the data instantly.
55
56	For most types of queries, there will be no overhead, especially on
57	multicore systems where your perl process can do other things while mysqld
58	does its stuff.
59
60	=head2 LIMITATIONS
61
62	This module only supports "standard" mysql connection handles - this
63	means unix domain or TCP sockets, and excludes SSL/TLS connections, named
64	pipes (windows) and shared memory (also windows). No support for these
65	connection types is planned, either.
66
67	=head1 FUNCTIONS
68
69	Coro::Mysql offers a single user-accessible function:
70
71	=over 4
72
73	=cut
74
75	package Coro::Mysql;
76
77	use strict qw(vars subs);
78	no warnings;
79
80	use Scalar::Util ();
81	use Carp qw(croak);
82
83	use Guard;
84	use Coro::Handle ();
85
86	# we need this extra indirection, as Coro doesn't support
87	# calling SLF-like functions via call_sv.
88
89	sub readable { &Coro::Handle::FH::readable }
90	sub writable { &Coro::Handle::FH::writable }
91
92	BEGIN {
93	our $VERSION = '1.02';
94
95	require XSLoader;
96	XSLoader::load Coro::Mysql::, $VERSION;
97	}
98
99	=item $DBH = Coro::Mysql::unblock $DBH
100
101	This function takes a DBI database handles and "patches" it
102	so it becomes compatible to Coro threads.
103
104	After that, it returns the patched handle - you should always use the
105	newly returned database handle.
106
107	It is safe to call this function on any database handle (or just about any
108	value), but it will only do anything to L<DBD::mysql> handles, others are
109	returned unchanged. That means it is harmless when applied to database
110	handles of other databases.
111
112	=cut
113
114	sub unblock {
115	my ($DBH) = @_;
116
117	if ($DBH->{Driver}{Name} eq "mysql") {
118	my $sock = $DBH->{sock};
119
120	open my $fh, "+>&" . $DBH->{sockfd}
121	or croak "Coro::Mysql unable to clone mysql fd";
122
123	$fh = Coro::Handle::unblock $fh;
124
125	_patch $sock, $DBH->{sockfd}, $fh, tied ${$fh};
126	}
127
128	$DBH
129	}
130
131	1;
132
133	=back
134
135	=head1 USAGE EXAMPLE
136
137	This example uses L<PApp::SQL> and L<Coro::on_enter> to implement a
138	function C<with_db>, that connects to a database, uses C<unblock> on the
139	resulting handle and then makes sure that C<$PApp::SQL::DBH> is set to the
140	(per-thread) database handle when the given thread is running (it does not
141	restore any previous value of $PApp::SQL::DBH, however):
142
143	use Coro;
144	use Coro::Mysql;
145	use PApp::SQL;
146
147	sub with_db($$$&) {
148	my ($database, $user, $pass, $cb) = @_;
149
150	my $dbh = Coro::Mysql::unblock DBI->connect ($database, $user, $pass)
151	or die $DBI::errstr;
152
153	Coro::on_enter { $PApp::SQL::DBH = $dbh };
154
155	$cb->();
156	}
157
158	This function makes it possible to easily use L<PApp::SQL> with
159	L<Coro::Mysql>, without worrying about database handles.
160
161	# now start 10 threads doing stuff
162	async {
163
164	with_db "DBI:mysql:test", "", "", sub {
165	sql_exec "update table set col = 5 where id = 7";
166
167	my $st = sql_exec \my ($id, $name),
168	"select id, name from table where name like ?",
169	"a%";
170
171	while ($st->fetch) {
172	...
173	}
174
175	my $id = sql_insertid sql_exec "insert into table values (1,2,3)";
176	# etc.
177	};
178
179	} for 1..10;
180
181	=head1 SEE ALSO
182
183	L<Coro>, L<PApp::SQL> (a user friendly but efficient wrapper around DBI).
184
185	=head1 AUTHOR
186
187	Marc Lehmann <schmorp@schmorp.de>
188	http://home.schmorp.de/
189
190	=cut
191