Correct pthread_t initialization and handling

Question

I understand that pthread_t should be treated as an opaque value, however I don't know how to initialize it when used as a class member, and how can I check for its validity.

Consider this code sample:

class MyClass
{
public:
    pthread_t thread;

    MyClass()
        : thread(0) // Wrong because pthread_t should be an opaque value,
                    // so how should I initialize it?
    {}

    ~MyClass()        
    {
        if( thread ) // Wrong, but how can I verify if it is valid?
            pthread_join(thread, NULL);
    }
};

I also understand that if pthread_create() fails, the pthread_t value may be inconsistent. So I should only rely on the return value from pthread_create(). But this means that I should keep this returned value along with pthread_t and use it to check thread validity? And in this case, how should I initialize in the class constructor this value?

class MyClass
{
public:
    pthread_t thread;
    int threadValid;

    MyClass()
        : thread(0), // Wrong because pthread_t should be an opaque value,
                     // so how should I initialize it?
        , threadValid(1) // pthread_create return zero in case of success,
                         // so I can initialize this to any nonzero value?
    {}

    ~MyClass()        
    {
        if( threadValid == 0 ) // Nonzero means thread invalid.
                               // Is this the correct approach?
        {
            pthread_join(thread, NULL);
            threadValid = 1;
        }
    }
};

I have a Windows API background, and there a thread has its HANDLE value, which may be initialized safely to NULL, and can be checked against NULL, and if CreateThread() fails, it just consistently returns NULL. There's no way, with pthreads, to keep this neat and simple approach?

Answer 1

pthread_t is a C type, so it must have a trivial default constructor; so you can just value-initialize it:

    : thread(), // ...

Your usage of threadValid seems somewhat confused. It would be better to make it a bool initially set to false and then only set it true once pthread_create succeeds.