Attempt to make DBD::mysql stable in async code

According to [^1] we have to care about connections:
[1] https://dev.mysql.com/doc/refman/5.7/en/c-api-threaded-clients.html

lib/DBDish/Connection.pm6

@@ -24,7 +24,10 @@ has $.last-rows is rw;
 method dispose() {
     $_.dispose for %!Statements.values;
     self._disconnect;
-    ?($.parent.Connections{self.WHICH}:delete);
+    #state $access = Lock.new;
+    #$access.protect: {
+        ?($.parent.Connections{self.WHICH}:delete);
+    #}
 }
 submethod DESTROY() {
     self.dispose;
@@ -41,7 +44,10 @@ method new(*%args) {
     my \con = ::?CLASS.bless(|%args);
     con.reset-err;
     con.?set-defaults;
-    %args<parent>.Connections{con.WHICH} = con;
+    #state $access = Lock.new;
+    #$access.protect: {
+        %args<parent>.Connections{con.WHICH} = con;
+    #}
 }
 
 method prepare(Str $statement, *%args) { ... }

lib/DBDish/mysql.pm6

@@ -1,19 +1,29 @@
 use v6;
+use NativeCall;
 need DBDish;
 # DBDish::mysql.pm6
 
 unit class DBDish::mysql:auth<mberends>:ver<0.1.4> does DBDish::Driver;
 use DBDish::mysql::Native;
 need DBDish::mysql::Connection;
 
+has %.mysql-init-per-thread;
+
 #------------------ methods to be called from DBIish ------------------
 method connect(Str :$host = 'localhost', Int :$port = 3306, Str :$database = 'mysql', Str :$user, Str :$password, Str :$socket ) {
+    state $access = Lock.new;
     my $connection;
-    my $mysql_client = MYSQL.mysql_init;
+    my $mysql_client;
+    # We call basially mysql_library_init here, which is exposed as mysql_server_init.
+    $access.protect: {
+        #%!mysql-init-per-thread{$*THREAD.id()} //=
+        mysql_server_init(0, Pointer, Pointer);
+        $mysql_client = MYSQL.mysql_init;
+    };
+    #my $mysql_client = MYSQL.mysql_init;
     my $errstr  = $mysql_client.mysql_error;
 
     unless $errstr {
-
         # real_connect() returns either the same client pointer or null
         my $result   = $mysql_client.mysql_real_connect(
             $host, $user, $password, $database, $port, $socket, 0

lib/DBDish/mysql/Native.pm6

@@ -196,6 +196,9 @@ class MYSQL is export is repr('CPointer') {
     method mysql_get_server_info(MYSQL:D:          --> Str) is native(LIB) { * }
 }
 
+# This is #define'd to be the same as mysql_library_init
+sub mysql_server_init(int32, Pointer, Pointer --> int32) is export is native(LIB) { * }
+
 sub mysql_get_client_version(--> uint32) is export is native(LIB) { * }
 sub mysql_get_client_info(--> Str)       is export is native(LIB) { * }
 

lib/DBIish.pm6

@@ -45,7 +45,8 @@ unit class DBIish:auth<mberends>:ver<0.5.9>;
         $d.connect(|%_);
     }
     method install-driver( $drivername ) {
-        my $d = %installed{$drivername} //= do {
+        state $access = Lock.new;
+        my $d = $access.protect: { %installed{$drivername} //= do {
             CATCH {
                 when X::CompUnit::UnsatisfiedDependency {
                     X::DBIish::DriverNotFound.new(:bogus($drivername)).fail;
@@ -65,7 +66,7 @@ unit class DBIish:auth<mberends>:ver<0.5.9>;
                 warn "$module doesn't do DBDish::Driver role!";
             }
             M.new(:parent($err-handler), |%($*DBI-DEFS<ConnDefaults>), |%_);
-        }
+        }};
         without $d { .throw; };
         $d;
     }

t/28-mysql-threaded.t

@@ -0,0 +1,26 @@
+use DBIish;
+use Test;
+
+plan 100;
+
+# This is meant to ensure that we load libmysqlclient.{so|dll} early enough.
+DBIish.install-driver('mysql', :RaiseError);
+
+await do for 1..100 {
+    start {
+        diag "Connecting to database for test $_ in thread $*THREAD.id()";
+        my $mysql = DBIish.connect('mysql',
+            :database<dbdishtest>,
+            :user<testuser>,
+            :password<testpass>,
+            :RaiseError,
+        );
+        my $time = rand * 10;
+        my $sth  = $mysql.prepare("SELECT $time, SLEEP($time)");
+        $sth.execute();
+
+        # sleepsorted output
+        pass "Slept about $time seconds for test $_ in thread $*THREAD.id()";
+        $mysql.dispose();
+    }
+}