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491 lines
14 KiB
491 lines
14 KiB
/**
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* Class definition for a MicroBitMessageBus.
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*
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* The MicroBitMessageBus handles all messages passed between components.
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*/
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#include "MicroBit.h"
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/**
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* Constructor.
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* Create a new Message Bus.
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*/
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MicroBitMessageBus::MicroBitMessageBus()
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{
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this->listeners = NULL;
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this->evt_queue_head = NULL;
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this->evt_queue_tail = NULL;
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this->nonce_val = 0;
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}
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/**
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* Returns a 'nonce' for use with the NONCE_ID channel of the message bus.
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*/
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uint16_t MicroBitMessageBus::nonce()
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{
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// In the global scheme of things, a terrible nonce generator.
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// However, for our purposes, this is simple and adequate for local use.
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// This would be a bad idea if our events were networked though - can you think why?
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return nonce_val++;
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}
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/**
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* Invokes a callback on a given MicroBitListener
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*
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* Internal wrapper function, used to enable
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* parameterised callbacks through the fiber scheduler.
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*/
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void async_callback(void *param)
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{
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MicroBitListener *listener = (MicroBitListener *)param;
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// OK, now we need to decide how to behave depending on our configuration.
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// If this a fiber f already active within this listener then check our
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// configuration to determine the correct course of action.
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//
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if (listener->flags & MESSAGE_BUS_LISTENER_BUSY)
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{
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// Drop this event, if that's how we've been configured.
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if (listener->flags & MESSAGE_BUS_LISTENER_DROP_IF_BUSY)
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return;
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// Queue this event up for later, if that's how we've been configured.
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if (listener->flags & MESSAGE_BUS_LISTENER_QUEUE_IF_BUSY)
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{
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listener->queue(listener->evt);
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return;
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}
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}
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// Determine the calling convention for the callback, and invoke...
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// C++ is really bad at this! Especially as the ARM compiler is yet to support C++ 11 :-/
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// Record that we have a fiber going into this listener...
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listener->flags |= MESSAGE_BUS_LISTENER_BUSY;
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while (1)
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{
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// Firstly, check for a method callback into an object.
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if (listener->flags & MESSAGE_BUS_LISTENER_METHOD)
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listener->cb_method->fire(listener->evt);
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// Now a parameterised C function
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else if (listener->flags & MESSAGE_BUS_LISTENER_PARAMETERISED)
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listener->cb_param(listener->evt, listener->cb_arg);
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// We must have a plain C function
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else
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listener->cb(listener->evt);
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// If there are more events to process, dequeue te next one and process it.
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if ((listener->flags & MESSAGE_BUS_LISTENER_QUEUE_IF_BUSY) && listener->evt_queue)
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{
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MicroBitEventQueueItem *item = listener->evt_queue;
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listener->evt = item->evt;
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listener->evt_queue = listener->evt_queue->next;
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delete item;
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}
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else
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break;
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}
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// The fiber of exiting... clear our state.
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listener->flags &= ~MESSAGE_BUS_LISTENER_BUSY;
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}
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/**
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* Queue the given event for processing at a later time.
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* Add the given event at the tail of our queue.
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*
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* @param The event to queue.
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*/
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void MicroBitMessageBus::queueEvent(MicroBitEvent &evt)
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{
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int processingComplete;
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// Firstly, process all handler regsitered as URGENT. These pre-empt the queue, and are useful for fast, high priority services.
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processingComplete = this->process(evt, MESSAGE_BUS_LISTENER_URGENT);
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if (!processingComplete)
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{
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// We need to queue this event for later processing...
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MicroBitEventQueueItem *item = new MicroBitEventQueueItem(evt);
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__disable_irq();
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if (evt_queue_tail == NULL)
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evt_queue_head = evt_queue_tail = item;
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else
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evt_queue_tail->next = item;
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__enable_irq();
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}
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}
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/**
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* Extract the next event from the front of the event queue (if present).
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* @return
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*
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* @param The event to queue.
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*/
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MicroBitEventQueueItem* MicroBitMessageBus::dequeueEvent()
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{
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MicroBitEventQueueItem *item = NULL;
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__disable_irq();
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if (evt_queue_head != NULL)
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{
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item = evt_queue_head;
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evt_queue_head = item->next;
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if (evt_queue_head == NULL)
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evt_queue_tail = NULL;
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}
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__enable_irq();
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return item;
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}
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/**
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* Periodic callback from MicroBit.
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* Process at least one event from the event queue, if it is not empty.
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* We then continue processing events until something appears on the runqueue.
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*/
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void MicroBitMessageBus::idleTick()
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{
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MicroBitEventQueueItem *item = this->dequeueEvent();
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// Whilst there are events to process and we have no useful other work to do, pull them off the queue and process them.
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while (item)
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{
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// send the event to all standard event listeners.
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this->process(item->evt);
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// Free the queue item.
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delete item;
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// If we have created some useful work to do, we stop processing.
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// This helps to minimise the number of blocked fibers we create at any point in time, therefore
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// also reducing the RAM footprint.
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if(!scheduler_runqueue_empty())
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break;
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// Pull the next event to process, if there is one.
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item = this->dequeueEvent();
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}
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}
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/**
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* Indicates whether or not we have any background work to do.
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* @ return 1 if there are any events waitingto be processed, 0 otherwise.
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*/
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int MicroBitMessageBus::isIdleCallbackNeeded()
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{
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return !(evt_queue_head == NULL);
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}
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/**
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* Queues the given event to be sent to all registered recipients.
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*
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* @param The event to send.
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*
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* n.b. THIS IS NOW WRAPPED BY THE MicroBitEvent CLASS FOR CONVENIENCE...
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*
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* Example:
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* @code
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* MicroBitEvent evt(id,MICROBIT_BUTTON_EVT_DOWN,ticks,CREATE_ONLY);
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* evt.fire();
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*
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* //OR YOU CAN DO THIS...
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* MicroBitEvent evt(id,MICROBIT_BUTTON_EVT_DOWN);
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* @endcode
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*/
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void MicroBitMessageBus::send(MicroBitEvent evt)
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{
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// We simply queue processing of the event until we're scheduled in normal thread context.
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// We do this to avoid the possibility of executing event handler code in IRQ context, which may bring
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// hidden race conditions to kids code. Queuing all events ensures causal ordering (total ordering in fact).
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this->queueEvent(evt);
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return;
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}
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/*
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* Deliver the given event to all registered event handlers.
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* Event handlers are called using the invoke() mechanism provided by the fier scheduler
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* This will attempt to call the event handler directly, but spawn a fiber should that
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* event handler attempt a blocking operation.
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* @param evt The event to be delivered.
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* @param mask The type of listeners to process (optional). Matches MicroBitListener flags. If not defined, all standard listeners will be processed.
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* @return The 1 if all matching listeners were processed, 0 if further processing is required.
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*/
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int MicroBitMessageBus::process(MicroBitEvent &evt, uint32_t mask)
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{
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MicroBitListener *l;
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int complete = 1;
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l = listeners;
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while (l != NULL)
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{
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if((l->id == evt.source || l->id == MICROBIT_ID_ANY) && (l->value == evt.value || l->value == MICROBIT_EVT_ANY))
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{
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if(l->flags & mask)
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{
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l->evt = evt;
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// OK, if this handler has regisitered itself as non-blocking, we just execute it directly...
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// This is normally only done for trusted system components.
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// Otherwise, we invoke it in a 'fork on block' context, that will automatically create a fiber
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// should the event handler attempt a blocking operation, but doesn't have the overhead
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// of creating a fiber needlessly. (cool huh?)
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if (l->flags & MESSAGE_BUS_LISTENER_NONBLOCKING)
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async_callback(l);
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else
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invoke(async_callback, l);
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}
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else
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{
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complete = 0;
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}
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}
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l = l->next;
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}
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return complete;
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}
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/**
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* Register a listener function.
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*
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* @param id The source of messages to listen for. Events sent from any other IDs will be filtered.
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* Use MICROBIT_ID_ANY to receive events from all components.
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*
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* @param value The value of messages to listen for. Events with any other values will be filtered.
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* Use MICROBIT_VALUE_ANY to receive events of any value.
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*
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* @param hander The function to call when an event is received.
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*
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* Example:
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* @code
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* void onButtonBClick(MicroBitEvent evt)
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* {
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* //do something
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* }
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* uBit.MessageBus.listen(MICROBIT_ID_BUTTON_B, MICROBIT_BUTTON_EVT_CLICK, onButtonBClick); // call function when ever a click event is detected.
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* @endcode
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*/
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void MicroBitMessageBus::listen(int id, int value, void (*handler)(MicroBitEvent), uint16_t flags)
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{
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if (handler == NULL)
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return;
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MicroBitListener *newListener = new MicroBitListener(id, value, handler, flags);
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if(!add(newListener))
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delete newListener;
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}
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void MicroBitMessageBus::listen(int id, int value, void (*handler)(MicroBitEvent, void*), void* arg, uint16_t flags)
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{
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if (handler == NULL)
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return;
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MicroBitListener *newListener = new MicroBitListener(id, value, handler, arg, flags);
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if(!add(newListener))
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delete newListener;
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}
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/**
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* Unregister a listener function.
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* Listners are identified by the Event ID, Event VALUE and handler registered using listen().
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*
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* @param id The Event ID used to register the listener.
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* @param value The Event VALUE used to register the listener.
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* @param handler The function used to register the listener.
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*
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*
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* Example:
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* @code
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* void onButtonBClick()
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* {
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* //do something
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* }
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*
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* uBit.MessageBus.ignore(MICROBIT_ID_BUTTON_B, MICROBIT_BUTTON_EVT_CLICK, onButtonBClick);
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* @endcode
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*/
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void MicroBitMessageBus::ignore(int id, int value, void (*handler)(MicroBitEvent))
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{
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if (handler == NULL)
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return;
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MicroBitListener listener(id, value, handler);
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remove(&listener);
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}
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/**
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* Unregister a listener function.
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* Listners are identified by the Event ID, Event VALUE and handler registered using listen().
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*
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* @param id The Event ID used to register the listener.
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* @param value The Event VALUE used to register the listener.
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* @param handler The function used to register the listener.
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*
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*
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* Example:
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* @code
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* void onButtonBClick(void *arg)
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* {
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* //do something
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* }
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*
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* uBit.MessageBus.ignore(MICROBIT_ID_BUTTON_B, MICROBIT_BUTTON_EVT_CLICK, onButtonBClick);
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* @endcode
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*/
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void MicroBitMessageBus::ignore(int id, int value, void (*handler)(MicroBitEvent, void*), void* arg)
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{
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if (handler == NULL)
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return;
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MicroBitListener listener(id, value, handler, arg);
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remove(&listener);
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}
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/**
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* Add the given MicroBitListener to the list of event handlers, unconditionally.
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* @param listener The MicroBitListener to validate.
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* @return 1 if the listener is valid, 0 otherwise.
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*/
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int MicroBitMessageBus::add(MicroBitListener *newListener)
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{
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MicroBitListener *l, *p;
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int methodCallback;
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//handler can't be NULL!
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if (newListener == NULL)
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return 0;
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l = listeners;
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// Firstly, we treat a listener as an idempotent operation. Ensure we don't already have this handler
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// registered in a that will already capture these events. If we do, silently ignore.
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// We always check the ID, VALUE and CB_METHOD fields.
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// If we have a callback to a method, check the cb_method class. Otherwise, the cb function point is sufficient.
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while (l != NULL)
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{
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methodCallback = (newListener->flags & MESSAGE_BUS_LISTENER_METHOD) && (l->flags & MESSAGE_BUS_LISTENER_METHOD);
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if (l->id == newListener->id && l->value == newListener->value && (methodCallback ? *l->cb_method == *newListener->cb_method : l->cb == newListener->cb))
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return 0;
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l = l->next;
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}
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// We have a valid, new event handler. Add it to the list.
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// if listeners is null - we can automatically add this listener to the list at the beginning...
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if (listeners == NULL)
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{
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listeners = newListener;
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return 1;
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}
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// We maintain an ordered list of listeners.
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// The chain is held stictly in increasing order of ID (first level), then value code (second level).
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// Find the correct point in the chain for this event.
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// Adding a listener is a rare occurance, so we just walk the list...
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p = listeners;
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l = listeners;
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while (l != NULL && l->id < newListener->id)
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{
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p = l;
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l = l->next;
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}
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while (l != NULL && l->id == newListener->id && l->value < newListener->value)
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{
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p = l;
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l = l->next;
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}
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//add at front of list
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if (p == listeners && (newListener->id < p->id || (p->id == newListener->id && p->value > newListener->value)))
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{
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newListener->next = p;
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//this new listener is now the front!
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listeners = newListener;
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}
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//add after p
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else
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{
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newListener->next = p->next;
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p->next = newListener;
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}
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return 1;
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}
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/**
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* Remove a MicroBitListener from the list that matches the given listener.
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* @param listener The MicroBitListener to validate.
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* @return The number of listeners removed from the list.
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*/
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int MicroBitMessageBus::remove(MicroBitListener *listener)
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{
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MicroBitListener *l, *p;
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int removed = 0;
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//handler can't be NULL!
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if (listener == NULL)
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return 0;
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l = listeners;
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p = NULL;
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// Walk this list of event handlers. Delete any that match the given listener.
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while (l != NULL)
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{
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if (l->id == listener->id && l->value == listener->value && ((listener->flags & MESSAGE_BUS_LISTENER_METHOD) == (l->flags & MESSAGE_BUS_LISTENER_METHOD)))
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{
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if(((listener->flags & MESSAGE_BUS_LISTENER_METHOD) && (*l->cb_method == *listener->cb_method)) ||
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((!(listener->flags & MESSAGE_BUS_LISTENER_METHOD) && l->cb == listener->cb)))
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{
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// Found a match. Remove from the list.
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if (p == NULL)
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listeners = l->next;
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else
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p->next = l->next;
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// delete the listener.
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MicroBitListener *t = l;
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l = l->next;
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delete t;
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removed++;
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continue;
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}
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}
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p = l;
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l = l->next;
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}
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return removed;
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}
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