Re: Thread save access to cout?

From:

=?ISO-8859-1?Q?Marcel_M=FCller?= <news.5.maazl@spamgourmet.com>

Newsgroups:

comp.lang.c++

Date:

Fri, 26 Feb 2010 15:40:42 +0100

Message-ID:

<4b87dd6b$0$7615$9b4e6d93@newsspool1.arcor-online.net>

Henryk wrote:

A side question:

class A {
  T someMember;
  Mutex theMutex;

  const T &getMember() {
    Lock lock(this->theMutex;
    return this->someMember;
  }
};

Is a call like this is thread-safe?

A a;
T aCopy = a.getMember(); // thread-safe copy-operation?

Is the destructor of lock inside A::getMember called AFTER the copy-
operation of A::someMember to aCopy?

No. The copy operation is done by the caller. This is past the sequence
point of the method call. If you want to force a copy to be taken in
synchronized context you have to make the return type of getMember a
value type rather than a reference.
const T getMember()

PS: The code shall run on an embedded system. I could just return an
object and not a reference in getMember to assure thread safety. But
this would result in an unnecessary copy operation, which is an issue
at that small processor.

One death you have to die. But if you have a reasonable optimizing
compiler, it might optimize this in some common cases.

I strongly recommend to switch to some common logging library. This will
address almost all of your problems.

Marcel