Re: Require Lock?
Am 14.02.2012 11:38, schrieb Hei:
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).
The C++ language doesn't define this, making this rather off-topic and better asked in comp.programming.threads (IIRC). That said, thread creation is generally a barrier, so anything done before creating the thread will be visible inside the thread.
There is a C++ issue though: The thread entry must be declared extern "C". A class-static works in many cases though, but formally it is undefined. I'd suggest using the new C++ threading facitilies btw, or Boost.Thread, both of which present a friendlier interface to multithreading in C++.
Good luck!
Uli
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