MTR_BUILD_THREAD=auto selects a value for MTR_BUILD_THREAD from a pool (WL#2690)

mysql-test/lib/mtr_unique.pl:
  Library file used by mysql-test-run.pl to determine unique test run identifiers.

mysql-test/lib/mtr_unique.pl

+#
+# This file is used from mysql-test-run.pl when choosing
+# port numbers and directories to use for running mysqld.
+#
+
+use strict;
+use Fcntl ':flock';
+
+#
+# Requested IDs are stored in a hash and released upon END.
+#
+my %mtr_unique_assigned_ids = ();
+END { 
+	while(my ($id,$file) = each(%mtr_unique_assigned_ids)) {
+		print "Autoreleasing $file:$id\n";
+		mtr_release_unique_id($file, $id);
+	}
+}
+
+#
+# Require a unique, numerical ID, given a file name (where all
+# requested IDs are stored), a minimum and a maximum value.
+#
+# We use flock to implement locking for the ID file and ignore
+# possible problems arising from lack of support for it on 
+# some platforms (it should work on most, and the possible
+# race condition would occur rarely). The proper solution for
+# this is a daemon that manages IDs, of course.
+#
+# If no unique ID within the specified parameters can be 
+# obtained, return undef.
+#
+sub mtr_require_unique_id($$$) {
+	my $file = shift;
+	my $min = shift;
+	my $max = shift;
+	my $ret = undef;
+
+	chmod 0777, "$file.sem";
+	open SEM, ">", "$file.sem" or die "can't write to $file.sem";
+	flock SEM, LOCK_EX or die "can't lock $file.sem";
+	if(! -e $file) {
+		open FILE, ">", $file or die "can't create $file";
+		close FILE;
+	}
+	chmod 0777, $file;
+	open FILE, "+<", $file or die "can't open $file";
+	select undef,undef,undef,0.2;
+	seek FILE, 0, 0;
+	my %taken = ();
+	while(<FILE>) {
+		chomp;
+		my ($id, $pid) = split / /;
+		$taken{$id} = $pid;
+	}
+	seek FILE, 0, 2;
+	for(my $i=$min; $i<=$max; ++$i) {
+		if(! exists $taken{$i}) {
+			print FILE "$i $$\n";
+			$ret = $i;
+			last;
+		}
+	}
+	close FILE;
+	flock SEM, LOCK_UN or warn "can't unlock $file.sem";
+	close SEM;
+	$mtr_unique_assigned_ids{$ret} = $file if defined $ret;
+	return $ret;
+}
+
+#
+# Require a unique ID like above, but sleep if no ID can be
+# obtained immediately.
+#
+sub mtr_require_unique_id_and_wait($$$) {
+	my $ret = mtr_require_unique_id($_[0],$_[1],$_[2]);
+	while(! defined $ret) {
+		sleep 10;
+		$ret = mtr_require_unique_id($_[0],$_[1],$_[2]);
+	}
+	return $ret;
+}
+
+#
+# Release a unique ID.
+#
+sub mtr_release_unique_id($$) {
+	my $file = shift;
+	my $myid = shift;
+
+	open SEM, ">", "$file.sem" or die "can't write to $file.sem";
+	flock SEM, LOCK_EX or die "can't lock $file.sem";
+	if(! -e $file) {
+		open FILE, ">", $file or die "can't create $file";
+		close FILE;
+	}
+	open FILE, "+<", $file or die "can't open $file";
+	select undef,undef,undef,0.2;
+	seek FILE, 0, 0;
+	my %taken = ();
+	while(<FILE>) {
+		chomp;
+		my ($id, $pid) = split / /;
+		$taken{$id} = $pid;
+	}
+	delete $taken{$myid};
+	seek FILE, 0, 0;
+	truncate FILE, 0 or die "can't truncate $file";
+	for my $k (keys %taken) {
+		print FILE $k . ' ' . $taken{$k} . "\n";
+	}
+	close FILE;
+	flock SEM, LOCK_UN or warn "can't unlock $file.sem";
+	close SEM;
+	delete $mtr_unique_assigned_ids{$myid};
+}
+
+1;
+

mysql-test/mysql-test-run.pl

@@ -85,6 +85,7 @@ require "lib/mtr_diff.pl";
 require "lib/mtr_match.pl";
 require "lib/mtr_misc.pl";
 require "lib/mtr_stress.pl";
+require "lib/mtr_unique.pl";
 
 $Devel::Trace::TRACE= 1;
 
@@ -449,6 +450,15 @@ sub initial_setup () {
   select(STDOUT);
   $| = 1;                       # Make unbuffered
 
+  # If so requested, we try to avail ourselves of a unique build thread number.
+  if ( $ENV{'MTR_BUILD_THREAD'} ) {
+    if ( lc($ENV{'MTR_BUILD_THREAD'}) eq 'auto' ) {
+      print "Requesting build thread... ";
+      $ENV{'MTR_BUILD_THREAD'} = mtr_require_unique_id_and_wait("/tmp/mysql-test-ports", 200, 299);
+      print "got ".$ENV{'MTR_BUILD_THREAD'}."\n";
+    }
+  }
+
   $glob_scriptname=  basename($0);
 
   # We require that we are in the "mysql-test" directory