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 replaces the I/O handlers for a database connection, with the
effect that "patched" database handles no longer block the all threads of
a process, but only the thread that does the request.

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, this module requires a header file that apparently isn't installed
everywhere (F<violite.h>), and therefore comes with it's own copy, which
might or might not be compatible to the F<violite.h> of your library -
when in doubt, make sure all the libmysqlclient header files are installed
and delete the F<violite.h> header that comes with this module.

On the good side, this module does a multitude of checks to ensure that
the libray versions match on the binary level, so on incompatibilities you
should expect an exception when trying to unblock a handle, rather than
data corruption.

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 to protetc access to a
shared database handle 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.

=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 = '1.2';

   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}, $DBH->{mysql_clientversion}, $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 HISTORY

This module was initially hacked together within a few hours on a long
flight to Malaysia, and seems to have worked ever since, with minor
adjustments for newer libmysqlclient libraries.

=head1 AUTHOR

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

=cut

Revision:	1.13
Committed:	Thu Oct 11 03:18:31 2012 UTC (11 years, 7 months ago) by root
Branch:	MAIN
Changes since 1.12:	+23 -12 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 replaces the I/O handlers for a database connection, with the
18	effect that "patched" database handles no longer block the all threads of
19	a process, but only the thread that does the request.
20
21	This can be used to make parallel sql requests using Coro, or to do other
22	stuff while mysql is rumbling in the background.
23
24	=head2 CAVEAT
25
26	Note that this module must be linked against exactly the same (shared,
27	possibly not working with all OSes) F<libmysqlclient> library as
28	DBD::mysql, otherwise it will not work.
29
30	Also, this module requires a header file that apparently isn't installed
31	everywhere (F<violite.h>), and therefore comes with it's own copy, which
32	might or might not be compatible to the F<violite.h> of your library -
33	when in doubt, make sure all the libmysqlclient header files are installed
34	and delete the F<violite.h> header that comes with this module.
35
36	On the good side, this module does a multitude of checks to ensure that
37	the libray versions match on the binary level, so on incompatibilities you
38	should expect an exception when trying to unblock a handle, rather than
39	data corruption.
40
41	Also, while this module makes database handles non-blocking, you still
42	cannot run multiple requests in parallel on the same database handle. If
43	you want to run multiple queries in parallel, you have to create multiple
44	database connections, one for each thread that runs queries. Not doing
45	so can corrupt your data - use a Coro::Semaphore to protetc access to a
46	shared database handle when in doubt.
47
48	If you make sure that you never run two or more requests in parallel, you
49	can freely share the database handles between threads, of course.
50
51	=head2 SPEED
52
53	This module is implemented in XS, and as long as mysqld replies quickly
54	enough, it adds no overhead to the standard libmysql communication
55	routines (which are very badly written, btw.). In fact, since it has a
56	more efficient buffering and allows requests to run in parallel, it often
57	decreases the actual time to run many queries considerably.
58
59	For very fast queries ("select 0"), this module can add noticable overhead
60	(around 15%, 7% when EV can be used) as it tries to switch to other
61	coroutines when mysqld doesn't deliver the data immediately, although,
62	again, when running queries in parallel, they will usually execute faster.
63
64	For most types of queries, there will be no extra latency, especially on
65	multicore systems where your perl process can do other things while mysqld
66	does its stuff.
67
68	=head2 LIMITATIONS
69
70	This module only supports "standard" mysql connection handles - this
71	means unix domain or TCP sockets, and excludes SSL/TLS connections, named
72	pipes (windows) and shared memory (also windows). No support for these
73	connection types is planned, either.
74
75	=head1 CANCELLATION
76
77	Cancelling a thread that is within a mysql query will likely make the
78	handle unusable. As far as Coro::Mysql is concerned, the handle can be
79	safely destroyed, but it's not clear how mysql itself will react to a
80	cancellation.
81
82	=head1 FUNCTIONS
83
84	Coro::Mysql offers a single user-accessible function:
85
86	=over 4
87
88	=cut
89
90	package Coro::Mysql;
91
92	use strict qw(vars subs);
93	no warnings;
94
95	use Scalar::Util ();
96	use Carp qw(croak);
97
98	use Guard;
99	use AnyEvent ();
100	use Coro ();
101	use Coro::AnyEvent (); # not necessary with newer Coro versions
102
103	# we need this extra indirection, as Coro doesn't support
104	# calling SLF-like functions via call_sv.
105
106	sub readable { &Coro::Handle::FH::readable }
107	sub writable { &Coro::Handle::FH::writable }
108
109	BEGIN {
110	our $VERSION = '1.2';
111
112	require XSLoader;
113	XSLoader::load Coro::Mysql::, $VERSION;
114	}
115
116	=item $DBH = Coro::Mysql::unblock $DBH
117
118	This function takes a DBI database handles and "patches" it
119	so it becomes compatible to Coro threads.
120
121	After that, it returns the patched handle - you should always use the
122	newly returned database handle.
123
124	It is safe to call this function on any database handle (or just about any
125	value), but it will only do anything to L<DBD::mysql> handles, others are
126	returned unchanged. That means it is harmless when applied to database
127	handles of other databases.
128
129	It is also safe to pass C<undef>, so code like this is works as expected:
130
131	my $dbh = DBI->connect ($database, $user, $pass)->Coro::Mysql::unblock
132	or die $DBI::errstr;
133
134	=cut
135
136	sub unblock {
137	my ($DBH) = @_;
138
139	if ($DBH && $DBH->{Driver}{Name} eq "mysql") {
140	my $sock = $DBH->{sock};
141
142	open my $fh, "+>&" . $DBH->{sockfd}
143	or croak "Coro::Mysql unable to clone mysql fd";
144
145	if (AnyEvent::detect ne "AnyEvent::Impl::EV" \|\| !_use_ev) {
146	require Coro::Handle;
147	$fh = Coro::Handle::unblock ($fh);
148	}
149
150	_patch $sock, $DBH->{sockfd}, $DBH->{mysql_clientversion}, $fh, tied ${$fh};
151	}
152
153	$DBH
154	}
155
156	1;
157
158	=back
159
160	=head1 USAGE EXAMPLE
161
162	This example uses L<PApp::SQL> and L<Coro::on_enter> to implement a
163	function C<with_db>, that connects to a database, uses C<unblock> on the
164	resulting handle and then makes sure that C<$PApp::SQL::DBH> is set to the
165	(per-thread) database handle when the given thread is running (it does not
166	restore any previous value of $PApp::SQL::DBH, however):
167
168	use Coro;
169	use Coro::Mysql;
170	use PApp::SQL;
171
172	sub with_db($$$&) {
173	my ($database, $user, $pass, $cb) = @_;
174
175	my $dbh = DBI->connect ($database, $user, $pass)->Coro::Mysql::unblock
176	or die $DBI::errstr;
177
178	Coro::on_enter { $PApp::SQL::DBH = $dbh };
179
180	$cb->();
181	}
182
183	This function makes it possible to easily use L<PApp::SQL> with
184	L<Coro::Mysql>, without worrying about database handles.
185
186	# now start 10 threads doing stuff
187	async {
188
189	with_db "DBI:mysql:test", "", "", sub {
190	sql_exec "update table set col = 5 where id = 7";
191
192	my $st = sql_exec \my ($id, $name),
193	"select id, name from table where name like ?",
194	"a%";
195
196	while ($st->fetch) {
197	...
198	}
199
200	my $id = sql_insertid sql_exec "insert into table values (1,2,3)";
201	# etc.
202	};
203
204	} for 1..10;
205
206	=head1 SEE ALSO
207
208	L<Coro>, L<PApp::SQL> (a user friendly but efficient wrapper around DBI).
209
210	=head1 HISTORY
211
212	This module was initially hacked together within a few hours on a long
213	flight to Malaysia, and seems to have worked ever since, with minor
214	adjustments for newer libmysqlclient libraries.
215
216	=head1 AUTHOR
217
218	Marc Lehmann <schmorp@schmorp.de>
219	http://home.schmorp.de/
220
221	=cut
222