Re: Require Lock?

From:

Pete Becker <pete@versatilecoding.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Tue, 14 Feb 2012 17:22:03 -0800 (PST)

Message-ID:

<2012021408394488286-pete@versatilecodingcom>

On 2012-02-14 10:38:38 +0000, Hei said:

Hi,
Here is my pesudocode:
class B {};
class A {
public:
  std::map<long, B*> m_myMap;
  A::A() {
      m_myMap[0] = new B();
      pthread_t threadID;
      pthread_create(&threadID, NULL, start, NULL);
  }
  static void* start(void*) {
      // use m_myMap[0] here
  }
}
I wonder whether m_myMap[0] may contain some invalid value since the
new thread might be in another CPU that might not see the change to
m_myMap[0] in the constructor yet (i.e. the change only 'exists' in
one of the CPU's caches).
Thanks in advance.

No idea (although it would be insane for this not to work). But if you create the new thread using C++11's thread object, the invocation of the thread object's constructor synchronizes with the beginning of the invocation of the called function, which is the formal language that says that all the changes you've made before creating the thread show up in the new thread.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The Standard C++ Library Extensions: a Tutorial and Reference (www.petebecker.com/tr1book)

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