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h.hasenack

Member

From: Nijmegen, Netherlands

Registered: 2012-08-01

Posts: 173

Website

Fix AV when using "dynamic" restservers

It turns out that when destroying a TDBRestserver, the registered TSQLVVirtualtableModule 's may already be destroyed...

This causes a very ugly AV in the  destructor

destructor TSQLRestServerDB.Destroy;
var i: integer;
begin
  try
    for i := 0 to high(fRegisteredVirtualTableModule) do
      if fRegisteredVirtualTableModule[i]<>nil then
        // to avoid GPF in TSQLVirtualTable.Destroy e.g.
        fRegisteredVirtualTableModule[i].fServer := nil; // MAY VERY WELL ACCESS A DESTROYEDE COMPONENT!!!
    inherited Destroy;
  finally
    try
      fStatementCache.ReleaseAllDBStatements;
    finally
      fOwnedDB.Free;
    end;
  end;
end;

Therefor I added an empty, virtual "unregister" method to TSQLRestServer, and an overriden one to TSQLRestServerDB:

// for de-registering a viirtual table module that gets destroyed for some reason
procedure TSQLRestServerDB.UnregisterVirtualTableModule(aVirtualTableObject:TSQLVirtualTableModule);
VAR i,cnt:integer;
begin
  cnt:=0;
  for i := low(fRegisteredVirtualTableModule) to high(fRegisteredVirtualTableModule) do
  begin
    if fRegisteredVirtualTableModule[i]=aVirtualTableObject then
      fRegisteredVirtualTableModule[i]:=nil;
  end;
end;

And added a destructor to TSQLVirtualTableModule:

destructor TSQLVirtualTableModule.Destroy;
VAR i:integer;
begin
  if assigned(FServer) then
    FServer.UnregisterVirtualTableModule(self);
  inherited; // for debugging purpose
end;

And now, my ugly AV has disappeared!

My suggestion would be to use an TObjectList or TList for maitaning a list of objects rather than the fRegisteredVirtualTableModule array of objects. Also  for a 'register/Unregister kind of way to manage the list of virtual tables in a TSQLRestServerDB. Hell, why not add an indexed property VirtualTableModule[idx:integer] and a VirtualTableModuleCOunt for that matter... Or maybe a (protected/public) VirtualTableModuleList:TObjectList ...

Regards - Hans

ab

Administrator

From: France

Registered: 2010-06-21

Posts: 14,660

Website

Re: Fix AV when using "dynamic" restservers

I am still not able to find out in which circumstances when destroying a TDBRestserver, the registered TSQLVVirtualtableModule 's may already be destroyed...

But I've committed a fix if this occurs, a bit diverse than yours (just overriding TSQLVirtualTableModuleDB.Destroy is enough), but the same idea.
See http://synopse.info/fossil/info/5680d09e81

Thanks for the report.

h.hasenack

Member

From: Nijmegen, Netherlands

Registered: 2012-08-01

Posts: 173

Website

Re: Fix AV when using "dynamic" restservers

Great!