delphi - TriticalSection TryEnter 方法始终返回 True

Question

在 TCriticalSection 上调用 TryEnter 方法时，结果始终为 true。当然，只有在能够获取锁的情况下才应该返回 true 吗？

var
  MyCritSect: TCriticalSection;

begin
  MyCritSect := TCriticalSection.Create;
  try
    //    MyCritSect.Enter;
    Writeln(BoolToStr(MyCritSect.TryEnter, True)); // This should return True
    Writeln(BoolToStr(MyCritSect.TryEnter, True)); // This should return False?
    Readln;
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end.

即使您取消注释 MyCritSect.Enter; 行，对 TryEnter 的两次调用仍会返回 True。

我使用的是 Delphi XE 和 Windows 10。

Answer 1

关键部分是 re-entrant locks 。来自 documentation :

When a thread owns a critical section, it can make additional calls to EnterCriticalSection or TryEnterCriticalSection without blocking its execution. This prevents a thread from deadlocking itself while waiting for a critical section that it already owns.

如果从不同的线程进行调用，并且第一个线程已经拥有锁，则对 TryEnter 的调用将会失败。