Hi

The TMultiReadExclusiveWriteSynchronizer implementation does not allow "read lock" promoting
to a "write lock". The program above hang in FPC 2.4 and 2.5.x while working in Delphi and
FPC 2.2.x. It hangs at the "x.Beginwrite();" instruction. The implementation clearly does
not support this scenario. It will be helpfull to note this in the documentation.

<code>
program test;
{$mode objfpc}{$H+}
uses
  SysUtils;
var
  x : TMultiReadExclusiveWriteSynchronizer;
begin
  x := TMultiReadExclusiveWriteSynchronizer.Create();
  x.Beginread();
    WriteLn('Beginread');
    x.Beginwrite();
      WriteLn('Beginwrite');
    x.Endwrite();
      WriteLn('Endwrite');
  x.Endread();
    WriteLn('Endread');
  ReadLn;
end.
</code>

19.02.2010 23:02, Inoussa OUEDRAOGO:

AFAIK entering exclusive lock without releasing multiple-read lock is very unsafe regarding deadlocks (Almost deadlock-guaranteed). Of course it is safe in the example, but why bother about special 1-thread scenario if multithreaded code will be unsafe anyway?

Nikolai

2010/2/19 Nikolai Zhubr :

The case here is to note that the FPC 2.4.0 (and trunck) implementation does not allows lock upgrading while Delphi, FPC 2.2.x does. This will free people
some debugging time , I talking from experience. The sample is just a test case to show the problem.