once.cpp

Go to the documentation of this file.

 
#define _RWSTD_LIB_SRC
#include <rw/_defs.h>
#include <rw/_mutex.h>
 
#include "once.h"
 
 
_RWSTD_NAMESPACE (__rw) {
 
 
extern "C" {
 
 
#ifdef _RWSTD_THREAD_ONCE
 
 
// implementation that relies on the system one-time initialization
// mechanism such as pthread_once()
_RWSTD_EXPORT int
__rw_once (__rw_once_t *once, void (*func)())
{
    _RWSTD_ASSERT (0 != once && 0 != func);
 
    return _RWSTD_THREAD_ONCE (once, func);
}
 
 
#elif defined (_RWSTD_NO_ATOMIC_OPS) && defined (_RWSTD_POSIX_THREADS)
 
 
// implementation that uses a mutex instead of pthread_once() or atomic
// operations
_RWSTD_EXPORT int
__rw_once (__rw_once_t *once, void (*func)())
{
    _RWSTD_ASSERT (0 != once && 0 != func);
 
    // _C_init may take on one of two valid values:
    // -1 for a properly initialized __rw_once_t object whose initializer
    //    hasn't run yet
    // +1 for ar __rw_once_t object whose initializer has already been
    //    executed
    // Any other value (including 0, for __rw_once_t objects that haven't
    // been properly initialized) is invalid.
 
    if (-1 == once->_C_init) {
 
        const int result = pthread_mutex_lock (&once->_C_mutex);
        if (result)
            return result;
 
        if (-1 == once->_C_init) {
 
            // entered by the first thread and only the first time around,
            // unless the initialization function throws
 
            _TRY {
                func ();
            }
            _CATCH (...) {
                pthread_mutex_unlock (&once->_C_mutex);
                _RETHROW;
            }
 
            once->_C_init += 2;
        }
 
        pthread_mutex_unlock (&once->_C_mutex);
    }
 
    // verify that initialization took place exactly once and help detect
    // uninitialized __rw_once_t objects to help catch problems on platforms
    // such as HP-UX that require pthread_once_t objects to be explicitly
    // initialized (i.e., not all bits tobe zeroed out) in order for
    // pthread_once() to succeed
    _RWSTD_ASSERT (1 == once->_C_init);
 
    return 0;
}
 
 
#elif defined (_RWSTD_REENTRANT)
 
 
// implementation that uses atomic operations
#ifndef _RWSTD_MSVC
_RWSTD_EXPORT int
__rw_once (__rw_once_t *once, void (*func)())
#else
_RWSTD_EXPORT int
__rw_once (__rw_once_t *once, void (*func)() throw (...)) throw (...)
#endif
{
    _RWSTD_ASSERT (0 != once && 0 != func);
 
    volatile int &init = once->_C_init;
 
restart:
 
    // cast init to int& (see STDCXX-792)
    // casting should be removed after fixing STDCXX-794
    if (init == 0 && 1 == _RWSTD_ATOMIC_PREINCREMENT (
            _RWSTD_CONST_CAST (int&, init), false)) {
 
        // entered by the first thread and only the first time around,
        // unless the initialization function throws
 
        _TRY {
            func ();
        }
        _CATCH (...) {
            _RWSTD_ATOMIC_PREDECREMENT (
                _RWSTD_CONST_CAST (int&, init), false);
            _RETHROW;
        }
 
        init = 1000;
    }
    else {
        // entered by the second and subsequent threads or on the second
        // and subsequent calls by the first thread after (or duing)
        // a successful initialization 
 
        for (int loop = 0; init < 1000; ++loop) {
            if (0 == init) {
                // first time initialization failed via an exception,
                // try again
                goto restart;
            }
 
            if (32 < loop) {
                // avoid wasting too many CPU cycles
                _RWSTD_THREAD_YIELD ();
            }
        }
    }
 
    return 0;
}
 
 
#else   // if !defined (_RWSTD_THREAD_ONCE)
 
 
// thread-unsafe implementation
_RWSTD_EXPORT int
__rw_once (__rw_once_t *once, void (*func)())
{
    _RWSTD_ASSERT (0 != once && 0 != func);
 
    // detect uninitialized __rw_once_t objects to help reveal problems
    // in reentrant code on platforms such as HP-UX that require
    // pthread_once_t objects to be explicitly initialized (i.e., not
    // all bits tobe zeroed out) in order for pthread_once() to succeed
    _RWSTD_ASSERT (-1 == once->_C_init || 1 == once->_C_init);
 
    if (once->_C_init == -1) {
 
        func ();
 
        once->_C_init = 1;
    }
 
    return 0;
}
 
#endif   // _RWSTD_THREAD_ONCE
 
}   // extern "C"
 
}   // namespace __rw