/[wait]/trunk/lib/WAIT/Table.pm

This is repository of my old source code which isn't updated any more. Go to git.rot13.org for current projects!

Diff of /trunk/lib/WAIT/Table.pm

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-revision 31 by laperla,
Sun Nov 12 01:26:10 2000 UTC
+revision 41 by laperla,
Mon Nov 13 20:25:49 2000 UTC
 Line 4
  # Author          : Ulrich Pfeifer
  # Created On      : Thu Aug  8 13:05:10 1996
  # Last Modified By: Ulrich Pfeifer
- # Last Modified On: Fri May 19 14:51:14 2000
+ # Last Modified On: Sun Nov 12 17:51:56 2000
  # Language        : CPerl
- # Update Count    : 133
+ # Update Count    : 148
  # Status          : Unknown, Use with caution!
  #
  # Copyright (c) 1996-1997, Ulrich Pfeifer
 Line 165 
 sub new {
      croak "Could not 'mkdir $self->{file}': $!\n";
    }
-   my $lockmgr = LockFile::Simple->make(-autoclean => 1);
-   # aquire a write lock
-   $self->{write_lock} = $lockmgr->lock($self->{file} . '/write')
-     or die "Can't lock '$self->{file}/write'";
    $self->{djk}      = $parm{djk}      if defined $parm{djk};
    $self->{layout}   = $parm{layout} || new WAIT::Parse::Base;
    $self->{access}   = $parm{access} if defined $parm{access};
-Line 178 
 sub new {
+Line 173 
 sub new {
    $self->{indexes}  = {};
    bless $self, $type;
+   # Checking for readers is not necessary, but let's go with the
+   # generic method.
+   $self->getlock(O_RDWR|O_CREAT); # dies when failing
    # Call create_index() and create_index() for compatibility
    for (@{$self->{keyset}||[]}) {
      #carp "Specification of indexes at table create time is deprecated";
 Line 323 
 Must be called via C<WAIT::Database::dro
  sub drop {
    my $self = shift;
+   unless ($self->{write_lock}){
+     warn "Cannot drop table without write lock. Nothing done";
+     return;
+   }
    if ((caller)[0] eq 'WAIT::Database') { # database knows about this
      $self->close;               # just make sure
      my $file = $self->{file};
      for (values %{$self->{indexes}}) {
        $_->drop;
      }
      unlink "$file/records";
+     rmdir "$file/read" or warn "Could not rmdir '$file/read'";
      # $self->unlock;
      ! (!-e $file or rmdir $file);
    } else {
-Line 382 
 sub open {
+Line 391 
 sub open {
                           $self->{mode}, 0664, $DB_BTREE);
      }
    }
-   # Locking
+   $self->getlock($self->{mode});
-   #
-   # We allow multiple readers to coexists.  But write access excludes
-   # all read access vice versa.  In practice read access on tables
-   # open for writing will mostly work ;-)
-   my $lockmgr = LockFile::Simple->make(-autoclean => 1);
-   # aquire a write lock. We might hold one acquired in create() already
-   $self->{write_lock} ||= $lockmgr->lock($self->{file} . '/write')
-     or die "Can't lock '$self->{file}/write'";
-   my $lockdir = $self->{file} . '/read';
-   unless (-d $lockdir) {
-     mkdir $lockdir, 0755 or die "Could not mkdir $lockdir: $!";
-   }
-   if ($self->{mode} & O_RDWR) {
-     # this is a hack.  We do not check for reopening ...
-     return $self if $self->{write_lock};
-     # If we actually want to write we must check if there are any readers
-     local *DIR;
-     opendir DIR, $lockdir or
-       die "Could not opendir '$lockdir': $!";
-     for my $lockfile (grep { -f "$lockdir/$_" } readdir DIR) {
-       # check if the locks are still valid.
-       # Since we are protected by a write lock, we could use a pline file.
-       # But we want to use the stale testing from LockFile::Simple.
-       if (my $lck = $lockmgr->trylock("$lockdir/$lockfile")) {
-         warn "Removing stale lockfile '$lockdir/$lockfile'";
-         $lck->release;
-       } else {
-         $self->{write_lock}->release;
-         die "Cannot write table '$file' while it's in use";
-       }
-     }
-     closedir DIR;
-   } else {
-     # this is a hack.  We do not check for reopening ...
-     return $self if $self->{read_lock};
-     # We are a reader. So we release the write lock
-     my $id = time;
-     while (-f "$lockdir/$id.lock") { # here assume ".lock" format!
-       $id++;
-     }
-     $self->{read_lock} = $lockmgr->lock("$lockdir/$id");
-     $self->{write_lock}->release;
-     delete $self->{write_lock};
-   }
    $self;
  }
-Line 693 
 sub close {
+Line 652 
 sub close {
 ;
  }
+ # Locking
+ #
+ # We allow multiple readers to coexists.  But write access excludes
+ # all read access and vice versa.  In practice read access on tables
+ # open for writing will mostly work ;-)
+ # If a "write" lock is requested, an existing "read" lock will be
+ # released.  If a "read" lock ist requested, an existing "write" lock
+ # will be released.  Requiring a lock already hold has no effect.
+ sub getlock {
+   my ($self, $mode) = @_;
+   # autoclean cleans on DESTROY, stale sends SIGZERO to the owner
+   #
+   my $lockmgr = LockFile::Simple->make(-autoclean => 1, -stale => 1);
+   my $file    = $self->{file} . '/records';
+   my $lockdir = $self->{file} . '/read';
+   unless (-d $lockdir) {
+     mkdir $lockdir, 0755 or die "Could not mkdir $lockdir: $!";
+   }
+   if ($mode & O_RDWR) {         # Get a write lock.  Release it again
+                                 # and die if there is any valid
+                                 # readers.
+     # Have a write lock already
+     return $self if $self->{write_lock};
+     if ($self->{read_lock}) {   # We are a becoming a writer now. So
+                                 # we release the read lock to avoid
+                                 # blocking ourselves.
+       $self->{read_lock}->release;
+       delete $self->{read_lock};
+     }
+     # Get the preliminary write lock
+     $self->{write_lock} = $lockmgr->lock($self->{file} . '/write')
+       or die "Can't lock '$self->{file}/write'";
+     # If we actually want to write we must check if there are any
+     # readers.  The write lock is confirmed if wen cannot find any
+     # valid readers.
+     local *DIR;
+     opendir DIR, $lockdir or
+       die "Could not opendir '$lockdir': $!";
+     for my $lockfile (grep { -f "$lockdir/$_" } readdir DIR) {
+       # Check if the locks are still valid.  Since we are protected by
+       # a write lock, we could use a plain file.  But we want to use
+       # the stale testing from LockFile::Simple.
+       if (my $lck = $lockmgr->trylock("$lockdir/$lockfile")) {
+         warn "Removing stale lockfile '$lockdir/$lockfile'";
+         $lck->release;
+       } else {                  # Found an active reader, rats!
+         $self->{write_lock}->release;
+         die "Cannot write table '$file' while it's in use";
+       }
+     }
+     closedir DIR;
+   } else {
+     # Have a read lock already
+     return $self if $self->{read_lock};
+     # Get the preliminary write lock to protect the directory
+     # operations.  If we already have a write lock, it will go.
+     $self->{write_lock} ||= $lockmgr->lock($self->{file} . '/write')
+       or die "Can't lock '$self->{file}/write'";
+     # Find a new read slot.  Maybe the plain file would be better?
+     my $id = time;
+     while (-f "$lockdir/$id.lock") { # here assume ".lock" format!
+       $id++;
+     }
+     $self->{read_lock} = $lockmgr->lock("$lockdir/$id")
+       or die "Can't lock '$lockdir/$id'";
+     # We are a reader now. So we release the write lock
+     $self->{write_lock}->release;
+     delete $self->{write_lock};
+   }
+   return $self;
+ }
  sub unlock {
    my $self = shift;
-Line 714 
 sub unlock {
+Line 760 
 sub unlock {
  sub DESTROY {
    my $self = shift;
-   warn "Table handle destroyed without closing it first"
+   if ($self->{write_lock} || $self->{read_lock}) {
-     if $self->{write_lock} || $self->{read_lock};
+     warn "Table handle destroyed without closing it first";
+     $self->unlock;
+   }
  }
  sub open_scan {

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