1. System Configuration - Header files & Compiler Directives
2. Thread Object

3. Event Object

The PiThreads library defines the class Event to provide event synchronization services. The class Event is defined in the header file event.h, which must be included after the inclusion of the thread.h header file and the #define WIN or #define POSIX statement. The PiThreads event object can be instantiated as either a manual-reset event or an automatic-reset event. A thread which attempts to wait on an event object is blocked if the event is in a non-signaled state, and permitted to continue when the event reaches a signaled state. The public member functions which serve as the interface to the event object can be seen below.

class Event

{

public:

Event();

Event(bool Manual_Reset);

void Signal();

void Reset();

void Pulse();

void Wait();

~Event();

};

An automatic-reset is instantiated with the default constructor, a manual event is instantiated by passing a value of true to the overloaded constructor Event(bool Manual_Reset). As noted above, a thread calls the Wait() member function to wait on an event. Signal() and Pulse() are used to release waiting threads, the semantics of Signal() and Pulse() differ depending on whether an automatic-reset or manual-reset event has been instantiated. Table 4 on the following page describes the behavioral differences between calls to Pulse() and Signal() between automatic-reset and manual-reset events.

Table 2 – Event Behavior

	Signal()	Pulse()
Automatic-Reset Event	If threads are waiting on the event, one is released and permitted to continue execution. The event is then automatically reset to a non-signaled state. If no threads are waiting on the event, the signaled state is held until the nest thread waits on the event	If any threads are waiting on the event one is released and the event is reset to a non-signaled state.
Manual-Reset Event	All threads waiting on the event are released, the event stays in a signaled state until Reset() is called	All threads waiting on the event are released, and the event then reverts to a non-signaled state

The following code instantiates a manual-reset event, an automatic-reset event, and threads to wait on each.

//#define WIN or POSIX

Event Auto;

Event Manual(true);

class ThreadDemo : public Thread

{

public:

ThreadDemo() : Thread() {}

void EntryRoutine(void)

{

Auto.Wait();

cout << “Released from automatic reset event” << endl;

}

void ExitRoutine(void)

{

Manual.Wait();

cout << “Released from manual-reset event” << endl;

}

};

void main()

{

ThreadDemo Waiters[5];

For(int I = 0; I < 5; I++)

Waiters.[I].Create();

For (int j = 0; j 5; j++)

Auto.Signal();

Manual.Signal();

}

Here a thread object has been created that waits on the automatic-reset event Auto in its entry routine and waits on the manual-reset event Manual in its exit routine. After five of these threads are initialized, five calls to Auto.Signal() release the threads blocked on the automatic-reset event. One call to the manual-reset event’s member function Signal() releases all threads blocked on the manual-reset event.

The PiThreads event synchronization object is process local and cannot be used to synchronize threads across multiple processes.