Completely reworked OS/2 thread implementation.

Moved wxConditionInternal from src/msw/thread.cpp to include/wx/thrimpl.cpp
        to give OS/2 the possibility to reuse the code.


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_4_BRANCH@22982 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/thrimpl.cpp

@@ -60,6 +60,153 @@ wxMutexError wxMutex::Unlock()
     return m_internal->Unlock();
 }
 
+// --------------------------------------------------------------------------
+// wxConditionInternal
+// --------------------------------------------------------------------------
+
+#if defined(__WXMSW__) || defined(__WXPM__)
+// Win32 and OS/2 don't have explicit support for the POSIX condition
+// variables and their events/event semaphores have quite different semantics,
+// so we reimplement the conditions from scratch using the mutexes and
+// semaphores
+#ifdef __WXPM__
+void InterlockedIncrement(LONG *num)
+{
+  ::DosEnterCritSec();
+  (*num)++;
+  ::DosExitCritSec();
+}
+#endif
+
+class wxConditionInternal
+{
+public:
+    wxConditionInternal(wxMutex& mutex);
+
+    bool IsOk() const { return m_mutex.IsOk() && m_semaphore.IsOk(); }
+
+    wxCondError Wait();
+    wxCondError WaitTimeout(unsigned long milliseconds);
+
+    wxCondError Signal();
+    wxCondError Broadcast();
+
+private:
+    // the number of threads currently waiting for this condition
+    LONG m_numWaiters;
+
+    // the critical section protecting m_numWaiters
+    wxCriticalSection m_csWaiters;
+
+    wxMutex& m_mutex;
+    wxSemaphore m_semaphore;
+};
+
+wxConditionInternal::wxConditionInternal(wxMutex& mutex)
+                   : m_mutex(mutex)
+{
+    // another thread can't access it until we return from ctor, so no need to
+    // protect access to m_numWaiters here
+    m_numWaiters = 0;
+}
+
+wxCondError wxConditionInternal::Wait()
+{
+    // increment the number of waiters
+    ::InterlockedIncrement(&m_numWaiters);
+
+    m_mutex.Unlock();
+
+    // a potential race condition can occur here
+    //
+    // after a thread increments nwaiters, and unlocks the mutex and before the
+    // semaphore.Wait() is called, if another thread can cause a signal to be
+    // generated
+    //
+    // this race condition is handled by using a semaphore and incrementing the
+    // semaphore only if 'nwaiters' is greater that zero since the semaphore,
+    // can 'remember' signals the race condition will not occur
+
+    // wait ( if necessary ) and decrement semaphore
+    wxSemaError err = m_semaphore.Wait();
+    m_mutex.Lock();
+
+    return err == wxSEMA_NO_ERROR ? wxCOND_NO_ERROR : wxCOND_MISC_ERROR;
+}
+
+wxCondError wxConditionInternal::WaitTimeout(unsigned long milliseconds)
+{
+    ::InterlockedIncrement(&m_numWaiters);
+
+    m_mutex.Unlock();
+
+    // a race condition can occur at this point in the code
+    //
+    // please see the comments in Wait(), for details
+
+    wxSemaError err = m_semaphore.WaitTimeout(milliseconds);
+
+    if ( err == wxSEMA_BUSY )
+    {
+        // another potential race condition exists here it is caused when a
+        // 'waiting' thread timesout, and returns from WaitForSingleObject, but
+        // has not yet decremented 'nwaiters'.
+        //
+        // at this point if another thread calls signal() then the semaphore
+        // will be incremented, but the waiting thread will miss it.
+        //
+        // to handle this particular case, the waiting thread calls
+        // WaitForSingleObject again with a timeout of 0, after locking
+        // 'nwaiters_mutex'. this call does not block because of the zero
+        // timeout, but will allow the waiting thread to catch the missed
+        // signals.
+        wxCriticalSectionLocker lock(m_csWaiters);
+
+        err = m_semaphore.WaitTimeout(0);
+
+        if ( err != wxSEMA_NO_ERROR )
+        {
+            m_numWaiters--;
+        }
+    }
+
+    m_mutex.Lock();
+
+    return err == wxSEMA_NO_ERROR ? wxCOND_NO_ERROR : wxCOND_MISC_ERROR;
+}
+
+wxCondError wxConditionInternal::Signal()
+{
+    wxCriticalSectionLocker lock(m_csWaiters);
+
+    if ( m_numWaiters > 0 )
+    {
+        // increment the semaphore by 1
+        if ( m_semaphore.Post() != wxSEMA_NO_ERROR )
+            return wxCOND_MISC_ERROR;
+
+        m_numWaiters--;
+    }
+
+    return wxCOND_NO_ERROR;
+}
+
+wxCondError wxConditionInternal::Broadcast()
+{
+    wxCriticalSectionLocker lock(m_csWaiters);
+
+    while ( m_numWaiters > 0 )
+    {
+        if ( m_semaphore.Post() != wxSEMA_NO_ERROR )
+            return wxCOND_MISC_ERROR;
+
+        m_numWaiters--;
+    }
+
+    return wxCOND_NO_ERROR;
+}
+#endif
+
 // ----------------------------------------------------------------------------
 // wxCondition
 // ----------------------------------------------------------------------------