--- Coro-Mysql/Mysql.pm 2009/05/30 06:58:22 1.2 +++ Coro-Mysql/Mysql.pm 2012/10/11 03:18:31 1.13 @@ -14,47 +14,75 @@ 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 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 -F library as DBD::mysql, otherwise it will not work. +Note that this module must be linked against exactly the same (shared, +possibly not working with all OSes) F library as +DBD::mysql, otherwise it will not work. + +Also, this module requires a header file that apparently isn't installed +everywhere (F), and therefore comes with it's own copy, which +might or might not be compatible to the F of your library - +when in doubt, make sure all the libmysqlclient header files are installed +and delete the F 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. +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 -cna 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. +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). +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%) as it tries to switch to other coroutines when mysqld doesn't -deliver the data instantly. +(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 overhead, especially on +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 @@ -68,7 +96,9 @@ use Carp qw(croak); use Guard; -use Coro::Handle (); +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. @@ -77,7 +107,7 @@ sub writable { &Coro::Handle::FH::writable } BEGIN { - our $VERSION = '0.1'; + our $VERSION = '1.2'; require XSLoader; XSLoader::load Coro::Mysql::, $VERSION; @@ -91,22 +121,34 @@ 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 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, 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) = @_; - my $sock = $DBH->{sock}; - open my $fh, "+>&" . $DBH->{sockfd} - or croak "Coro::Mysql unable to clone mysql fd"; + if ($DBH && $DBH->{Driver}{Name} eq "mysql") { + my $sock = $DBH->{sock}; - $fh = Coro::Handle::unblock $fh; + open my $fh, "+>&" . $DBH->{sockfd} + or croak "Coro::Mysql unable to clone mysql fd"; - _patch $sock, $DBH->{sockfd}, tied ${$fh}; - $DBH->{private_Coro_Mysql} = guard { - _unpatch $sock; - undef $fh; - }; + 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}; + } $DBH } @@ -115,6 +157,62 @@ =back +=head1 USAGE EXAMPLE + +This example uses L and L to implement a +function C, that connects to a database, uses C on the +resulting handle and then makes sure that C<$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 with +L, 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, L (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