--- loncom/lond	2006/01/31 04:40:12	1.310
+++ loncom/lond	2006/01/31 16:12:12	1.313
@@ -2,7 +2,7 @@
 # The LearningOnline Network
 # lond "LON Daemon" Server (port "LOND" 5663)
 #
-# $Id: lond,v 1.310 2006/01/31 04:40:12 albertel Exp $
+# $Id: lond,v 1.313 2006/01/31 16:12:12 albertel Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -53,13 +53,15 @@ use LONCAPA::ConfigFileEdit;
 use LONCAPA::lonlocal;
 use LONCAPA::lonssl;
 use Fcntl qw(:flock);
+use Symbol;
 
 my $DEBUG = 0;		       # Non zero to enable debug log entries.
 
 my $status='';
 my $lastlog='';
+my $lond_max_wait_time = 13;
 
-my $VERSION='$Revision: 1.310 $'; #' stupid emacs
+my $VERSION='$Revision: 1.313 $'; #' stupid emacs
 my $remoteVERSION;
 my $currenthostid="default";
 my $currentdomainid;
@@ -971,23 +973,13 @@ sub tie_domain_hash {
     
     my $user_top_dir   = $perlvar{'lonUsersDir'};
     my $domain_dir     = $user_top_dir."/$domain";
-    my $resource_file  = $domain_dir."/$namespace.db";
-    my %hash;
-    if(tie(%hash, 'GDBM_File', $resource_file, $how, 0640)) {
-	if (defined($loghead)) {	# Need to log the operation.
-	    my $logFh = IO::File->new(">>$domain_dir/$namespace.hist");
-	    if($logFh) {
-		my $timestamp = time;
-		print $logFh "$loghead:$timestamp:$logtail\n";
-	    }
-	    $logFh->close;
-	}
-	return \%hash;		# Return the tied hash.
-    } else {
-	return undef;		# Tie failed.
-    }
+    my $resource_file  = $domain_dir."/$namespace";
+    return &_locking_hash_tie($resource_file,$namespace,$how,$loghead,$logtail);
 }
 
+sub untie_domain_hash {
+    return &_locking_hash_untie(@_);
+}
 #
 #   Ties a user's resource file to a hash.  
 #   If necessary, an appropriate history
@@ -1013,18 +1005,27 @@ sub tie_user_hash {
     $namespace=~s/\//\_/g;	# / -> _
     $namespace=~s/\W//g;		# whitespace eliminated.
     my $proname     = propath($domain, $user);
-   
-    #  Tie the database.
-    
+
+    my $file_prefix="$proname/$namespace";
+    return &_locking_hash_tie($file_prefix,$namespace,$how,$loghead,$what);
+}
+
+sub untie_user_hash {
+    return &_locking_hash_untie(@_);
+}
+
+# internal routines that handle the actual tieing and untieing process
+
+sub _do_hash_tie {
+    my ($file_prefix,$namespace,$how,$loghead,$what) = @_;
     my %hash;
-    if(tie(%hash, 'GDBM_File', "$proname/$namespace.db",
-	   $how, 0640)) {
+    if(tie(%hash, 'GDBM_File', "$file_prefix.db", $how, 0640)) {
 	# If this is a namespace for which a history is kept,
 	# make the history log entry:    
 	if (($namespace !~/^nohist\_/) && (defined($loghead))) {
 	    my $args = scalar @_;
-	    Debug(" Opening history: $namespace $args");
-	    my $hfh = IO::File->new(">>$proname/$namespace.hist"); 
+	    Debug(" Opening history: $file_prefix $args");
+	    my $hfh = IO::File->new(">>$file_prefix.hist"); 
 	    if($hfh) {
 		my $now = time;
 		print $hfh "$loghead:$now:$what\n";
@@ -1035,7 +1036,76 @@ sub tie_user_hash {
     } else {
 	return undef;
     }
+}
+
+sub _do_hash_untie {
+    my ($hashref) = @_;
+    my $result = untie(%$hashref);
+    return $result;
+}
+
+{
+    my $sym;
+
+    sub _locking_hash_tie {
+	my ($file_prefix,$namespace,$how,$loghead,$what) = @_;
+
+	my ($lock);
     
+	if ($how eq &GDBM_READER()) {
+	    $lock=LOCK_SH;
+	    $how=$how|&GDBM_NOLOCK();
+	    #if the db doesn't exist we can't read from it
+	    if (! -e "$file_prefix.db") {
+		$! = 2;
+		return undef;
+	    }
+	} elsif ($how eq &GDBM_WRCREAT()) {
+	    $lock=LOCK_EX;
+	    $how=$how|&GDBM_NOLOCK();
+	    if (! -e "$file_prefix.db") {
+		# doesn't exist but we need it to in order to successfully
+                # lock it so bring it into existance
+		open(TOUCH,">>$file_prefix.db");
+		close(TOUCH);
+	    }
+	} else {
+	    &logthis("Unknown method $how for $file_prefix");
+	    die();
+	}
+    
+	&logthis("$$ for $namespace");
+	$sym=&Symbol::gensym();
+	open($sym,"$file_prefix.db");
+	&logthis("$$ for $namespace attempt lock");
+	my $failed=0;
+	eval {
+	    local $SIG{__DIE__}='DEFAULT';
+	    local $SIG{ALRM}=sub { 
+		$failed=1;
+		die("failed lock");
+	    };
+	    alarm($lond_max_wait_time);
+	    flock($sym,$lock);
+	    alarm(0);
+	};
+	if ($failed) {
+	    &logthis("$$ for $namespace got failed lock");
+	    $! = 100; # throwing error # 100
+	    return undef;
+	}
+	&logthis("$$ for $file_prefix.db got lock");
+	return &_do_hash_tie($file_prefix,$namespace,$how,$loghead,$what);
+    }
+
+    sub _locking_hash_untie {
+	my ($hashref) = @_;
+	my $result = untie(%$hashref);
+	flock($sym,LOCK_UN);
+	close($sym);
+	undef($sym);
+	return $result;
+    }
 }
 
 #   read_profile
@@ -1068,7 +1138,7 @@ sub read_profile {
 	    $qresult.="$hashref->{$queries[$i]}&";    # Presumably failure gives empty string.
 	}
 	$qresult=~s/\&$//;              # Remove trailing & from last lookup.
-	if (untie %$hashref) {
+	if (&untie_user_hash($hashref)) {
 	    return $qresult;
 	} else {
 	    return "error: ".($!+0)." untie (GDBM) Failed";
@@ -2377,7 +2447,7 @@ sub put_user_profile_entry {
 		my ($key,$value)=split(/=/,$pair);
 		$hashref->{$key}=$value;
 	    }
-	    if (untie(%$hashref)) {
+	    if (&untie_user_hash($hashref)) {
 		&Reply( $client, "ok\n", $userinput);
 	    } else {
 		&Failure($client, "error: ".($!+0)." untie(GDBM) failed ".
@@ -2440,7 +2510,7 @@ sub newput_user_profile_entry {
 	$hashref->{$key}=$value;
     }
 
-    if (untie(%$hashref)) {
+    if (&untie_user_hash($hashref)) {
 	&Reply( $client, "ok\n", $userinput);
     } else {
 	&Failure($client, "error: ".($!+0)." untie(GDBM) failed ".
@@ -2493,7 +2563,7 @@ sub increment_user_value_handler {
                     }
                 }
 	    }
-	    if (untie(%$hashref)) {
+	    if (&untie_user_hash($hashref)) {
 		&Reply( $client, "ok\n", $userinput);
 	    } else {
 		&Failure($client, "error: ".($!+0)." untie(GDBM) failed ".
@@ -2560,7 +2630,7 @@ sub roles_put_handler {
 			       $auth_type);
 	    $hashref->{$key}=$value;
 	}
-	if (untie($hashref)) {
+	if (&untie_user_hash($hashref)) {
 	    &Reply($client, "ok\n", $userinput);
 	} else {
 	    &Failure( $client, "error: ".($!+0)." untie(GDBM) Failed ".
@@ -2611,7 +2681,7 @@ sub roles_delete_handler {
 	foreach my $key (@rolekeys) {
 	    delete $hashref->{$key};
 	}
-	if (untie(%$hashref)) {
+	if (&untie_user_hash(%$hashref)) {
 	    &Reply($client, "ok\n", $userinput);
 	} else {
 	    &Failure( $client, "error: ".($!+0)." untie(GDBM) Failed ".
@@ -2752,7 +2822,7 @@ sub delete_profile_entry {
 	foreach my $key (@keys) {
 	    delete($hashref->{$key});
 	}
-	if (untie(%$hashref)) {
+	if (&untie_user_hash(%$hashref)) {
 	    &Reply($client, "ok\n", $userinput);
 	} else {
 	    &Failure($client, "error: ".($!+0)." untie(GDBM) Failed ".
@@ -2794,7 +2864,7 @@ sub get_profile_keys {
 	foreach my $key (keys %$hashref) {
 	    $qresult.="$key&";
 	}
-	if (untie(%$hashref)) {
+	if (&untie_user_hash(%$hashref)) {
 	    $qresult=~s/\&$//;
 	    &Reply($client, "$qresult\n", $userinput);
 	} else {
@@ -2855,7 +2925,7 @@ sub dump_profile_database {
 	    $data{$symb}->{$param}=$value;
 	    $data{$symb}->{'v.'.$param}=$v;
 	}
-	if (untie(%$hashref)) {
+	if (&untie_user_hash($hashref)) {
 	    while (my ($symb,$param_hash) = each(%data)) {
 		while(my ($param,$value) = each (%$param_hash)){
 		    next if ($param =~ /^v\./);       # Ignore versions...
@@ -2947,7 +3017,7 @@ sub dump_with_regexp {
 		}
 	    }
 	}
-	if (untie(%$hashref)) {
+	if (&untie_user_hash($hashref)) {
 	    chop($qresult);
 	    &Reply($client, "$qresult\n", $userinput);
 	} else {
@@ -3009,7 +3079,7 @@ sub store_handler {
 	    $hashref->{"$version:$rid:timestamp"}=$now;
 	    $allkeys.='timestamp';
 	    $hashref->{"$version:keys:$rid"}=$allkeys;
-	    if (untie($hashref)) {
+	    if (&untie_user_hash($hashref)) {
 		&Reply($client, "ok\n", $userinput);
 	    } else {
 		&Failure($client, "error: ".($!+0)." untie(GDBM) Failed ".
@@ -3076,7 +3146,7 @@ sub restore_handler {
 		$qresult.="$scope:$key=".$hashref->{"$scope:$rid:$key"}."&";
 	    }                                  
 	}
-	if (untie(%$hashref)) {
+	if (&untie_user_hash($hashref)) {
 	    $qresult=~s/\&$//;
 	    &Reply( $client, "$qresult\n", $userinput);
 	} else {
@@ -3309,7 +3379,7 @@ sub put_course_id_handler {
             }
 	    $hashref->{$key}=$courseinfo.':'.$now;
 	}
-	if (untie(%$hashref)) {
+	if (&untie_domain_hash($hashref)) {
 	    &Reply( $client, "ok\n", $userinput);
 	} else {
 	    &Failure($client, "error: ".($!+0)
@@ -3425,7 +3495,7 @@ sub dump_course_id_handler {
                 $qresult.=$key.'='.$descr.':'.$inst_code.':'.$owner.'&';
             }
 	}
-	if (untie(%$hashref)) {
+	if (&untie_domain_hash($hashref)) {
 	    chop($qresult);
 	    &Reply($client, "$qresult\n", $userinput);
 	} else {
@@ -3474,7 +3544,7 @@ sub put_id_handler {
 	    my ($key,$value)=split(/=/,$pair);
 	    $hashref->{$key}=$value;
 	}
-	if (untie(%$hashref)) {
+	if (&untie_domain_hash($hashref)) {
 	    &Reply($client, "ok\n", $userinput);
 	} else {
 	    &Failure($client, "error: ".($!+0)." untie(GDBM) Failed ".
@@ -3523,7 +3593,7 @@ sub get_id_handler {
 	for (my $i=0;$i<=$#queries;$i++) {
 	    $qresult.="$hashref->{$queries[$i]}&";
 	}
-	if (untie(%$hashref)) {
+	if (&untie_domain_hash($hashref)) {
 	    $qresult=~s/\&$//;
 	    &Reply($client, "$qresult\n", $userinput);
 	} else {
@@ -3567,7 +3637,7 @@ sub put_dcmail_handler {
         my ($key,$value)=split(/=/,$what);
         $hashref->{$key}=$value;
     }
-    if (untie(%$hashref)) {
+    if (&untie_domain_hash($hashref)) {
         &Reply($client, "ok\n", $userinput);
     } else {
         &Failure($client, "error: ".($!+0)." untie(GDBM) Failed ".
@@ -3647,7 +3717,7 @@ sub dump_dcmail_handler {
                 $qresult.=$key.'='.$value.'&';
             }
         }
-        if (untie(%$hashref)) {
+        if (&untie_domain_hash($hashref)) {
             chop($qresult);
             &Reply($client, "$qresult\n", $userinput);
         } else {
@@ -3694,7 +3764,7 @@ sub put_domainroles_handler {
             my ($key,$value)=split(/=/,$pair);
             $hashref->{$key}=$value;
         }
-        if (untie(%$hashref)) {
+        if (&untie_domain_hash($hashref)) {
             &Reply($client, "ok\n", $userinput);
         } else {
             &Failure($client, "error: ".($!+0)." untie(GDBM) Failed ".
@@ -3775,7 +3845,7 @@ sub dump_domainroles_handler {
                 $qresult.=$key.'='.$value.'&';
             }
         }
-        if (untie(%$hashref)) {
+        if (&untie_domain_hash($hashref)) {
             chop($qresult);
             &Reply($client, "$qresult\n", $userinput);
         } else {
@@ -5629,7 +5699,7 @@ sub get_chat {
 				 &GDBM_READER());
     if ($hashref) {
 	@entries=map { $_.':'.$hashref->{$_} } sort(keys(%$hashref));
-	untie(%$hashref);
+	&untie_user_hash($hashref);
     }
     my @participants=();
     my $cutoff=time-60;
@@ -5642,7 +5712,7 @@ sub get_chat {
 		push(@participants, 'active_participant:'.$user);
             }
         }
-        untie(%$hashref);
+        &untie_user_hash($hashref);
     }
     return (@participants,@entries);
 }
@@ -5679,7 +5749,7 @@ sub chat_add {
 	    }
 	    close(CHATLOG);
 	}
-	untie(%$hashref);
+	&untie_user_hash($hashref);
     }
 }