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GTM.pm  view on Meta::CPAN

  with one of them, then the others will behave normally (their writes
  will take effect immediately).

  Also note that until a txncommit() is performed, everyone who views 
  the data that has been set since a txnstart() will see the OLD data,
  not the stuff that is in the process of being written.

=head3 LOCKING

  $status = $dblink->lock(@name,$seconds);   # Lock a database node
  $status = $dblink->unlock(@name);          # Unlock something locked prior

  seconds: the last parameter to lock() is the number of seconds to
    wait to get a lock before giving up.  This is important as GT.M
    reserves the use of signals for itself and using SIGALRM may 
    cause problems.

    Specifying a seconds count of 0 will make the locking attempt 
    fail immediately if another lock exists.
  
    Specifying a seconds count of -1 will make the locking attempt
    wait forever for a conflicting lock to be released.  This can 
    lead to deadlock, so use with caution.

  If you specify a global name, you MUST specify a seconds count.
  Bad things will happen to you if you don't.

  In order to work gracefully with other processes that are attempting
  to update data in the GTM datastore, you can request locks on database
  nodes.  Locks are advisory (meaning that it's possible to write to a
  "locked" node if you don't bother to ask for your lock first).  Locks
  are automatically released when your process exits.

  Lock on a higher-level resources conflict with lower-level ones.

  Examples:
    (Process 1)  $db = new GTMDB("TOPNODE");
                 $db->lock("MYNODE","A",0);  # Lock (TOPNODE.MYNODE.A)

    (Process 2)  $db = new GTMDB("TOPNODE");
                 $db->lock("MYNODE",0);      # Lock (TOPNODE.MYNODE)
                 # Fails because process 1 has a conflicting lock

  Note that you can always get locks to resources that you have previously
  locked, or lock a lower level resource.

=head2 FUNCTION LIST

  Conventions: 

    When a function takes '@name' as a parameter, or returns it as output,
    @name is a list that makes up the name of a database node.  Any node
    can store data as well as have child nodes.  See the examples above
    for explicit usage.  If unspecified, functions that operate on @name
    will operate on the main node linked to during new()

GTM.pm  view on Meta::CPAN

 
  $status = $db_obj->kill(@name);      # Destroys node and all subnodes
  $status = $db_obj->ks(@name);        # Destroys all sub-nodes only
  $status = $db_obj->kv(@name);        # Destroys current node only

  $status = $dblink->txnstart();       # Begin a transaction
  $status = $dblink->txnabort();       # Abort a transaction, make no changes
  $status = $dblink->txncommit();      # Save all set/kills made during txn

  $status = $dblink->lock(@name,$seconds);   # Lock a database node
  $status = $dblink->unlock(@name);          # Unlock locked database node

  $status = $db_obj->merge(@srcname [ ,undef,@dstname ]); 
      # Copies nodes in @srcname into @dstname, overwriting collisions 
      # if unspecified, @dstname is assumed to be the main node
   
  $status = $db_obj->clobber(@srcname [ ,undef,@dstname ]); 
      # Makes @dstname an exact clone of @srcname

  $db_obj->clobber() and $db_obj->merge() can take another $db_obj as a source.

t/8_locks.t  view on Meta::CPAN

BEGIN { use_ok('Db::GTM') };
$ENV{'GTMCI'}="/usr/local/gtm/xc/calltab.ci" unless $ENV{'GTMCI'};

my($childpid); if( $childpid = fork ) {

  my $db = new GTMDB('SPZ');
  sleep 1; # Give the child process a chance to obtain its lock
  ok( !$db->lock("LOCKFREE",0), "OK to lock something no-one else wants" );
  ok( $db->lock("LOCKTAKEN",0), 
      "Can\'t lock something already locked by another process."
  );

} else {

  my $db = new GTMDB('SPZ');
  $db->lock("LOCKTAKEN",0);
  sleep 3; # Give parent process a chance to try locking it while we have it
  exit;
}