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microbit: Added C++ member function callback support into MicroBitMessageBus 

Event callbacks can now be transparently added to any C++ member function
matching the MicroBitMessageBud signature:  void fn(MicroBitEvent e)
master
Joe Finney 2015-09-10 00:04:27 +01:00
parent 8e1a15c79f
commit 8ea2e953c8
8 changed files with 367 additions and 92 deletions
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77
inc/MemberFunctionCallback.h Normal file
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@ -0,0 +1,77 @@
#ifndef MEMBER_FUNCTION_CALLBACK_H
#define MEMBER_FUNCTION_CALLBACK_H
#include "mbed.h"
#include "MicroBitEvent.h"
/**
* Class definition for a MemberFunctionCallback.
*
* C++ member functions (also known as methods) have a more complex
* representation than normal C functions. This allows a referene to
* a C++ member function to be stored then called at a later date.
*
* This class is used extensively by the MicroBitMessageBus to deliver
* events to C++ methods.
*/
class MemberFunctionCallback
{
private:
void* object;
uint32_t method[4];
void (*invoke)(void *object, uint32_t *method, MicroBitEvent e);
template <typename T> static void methodCall(void* object, uint32_t*method, MicroBitEvent e);
public:
/**
* Constructor. Creates a MemberFunctionCallback based on a pointer to given method.
* @param object The object the callback method should be invooked on.
* @param method The method to invoke.
*/
template <typename T> MemberFunctionCallback(T* object, void (T::*method)(MicroBitEvent e));
/**
* Comparison of two MemberFunctionCallback objects.
* @return TRUE if the given MemberFunctionCallback is equivalent to this one. FALSE otherwise.
*/
bool operator==(const MemberFunctionCallback &mfc);
/**
* Calls the method reference held by this MemberFunctionCallback.
* @param e The event to deliver to the method
*/
void fire(MicroBitEvent e);
};
/**
* Constructor. Creates a representation of a pointer to a C++ member function (method).
* @param object The object the callback method should be invooked on.
* @param method The method to invoke.
*/
template <typename T>
MemberFunctionCallback::MemberFunctionCallback(T* object, void (T::*method)(MicroBitEvent e))
{
this->object = object;
memclr(this->method, sizeof(method));
memcpy(this->method, &method, sizeof(method));
invoke = &MemberFunctionCallback::methodCall<T>;
}
/**
* Template to create static methods capable of invoking a C++ member function (method)
* based on the given paramters.
*/
template <typename T>
void MemberFunctionCallback::methodCall(void *object, uint32_t *method, MicroBitEvent e)
{
T* o = (T*)object;
void (T::*m)(MicroBitEvent);
memcpy(&m, method, sizeof(m));
(o->*m)(e);
}
#endif

9
inc/MicroBit.h
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@ -4,10 +4,6 @@
#include "mbed.h"
#include "MicroBitConfig.h"
#include "MicroBitPanic.h"
#include "ble/BLE.h"
#include "ble/services/DeviceInformationService.h"
#include "ErrorNo.h"
#include "MicroBitHeapAllocator.h"
@ -15,9 +11,10 @@
#include "MicroBitFiber.h"
#include "ManagedType.h"
#include "ManagedString.h"
#include "MicroBitEvent.h"
#include "MicroBitFont.h"
#include "MicroBitImage.h"
#include "MicroBitEvent.h"
#include "MicroBitMessageBus.h"
#include "DynamicPwm.h"
#include "MicroBitComponent.h"
@ -31,6 +28,8 @@
#include "MicroBitCompass.h"
#include "MicroBitAccelerometer.h"
#include "ble/BLE.h"
#include "ble/services/DeviceInformationService.h"
#include "MicroBitDFUService.h"
#include "MicroBitEventService.h"
#include "ExternalEvents.h"

81
inc/MicroBitListener.h Normal file
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@ -0,0 +1,81 @@
#ifndef MICROBIT_LISTENER_H
#define MICROBIT_LISTENER_H
#include "mbed.h"
#include "MicroBitEvent.h"
// MessageBusListener flags...
#define MESSAGE_BUS_LISTENER_PARAMETERISED 0x0001
#define MESSAGE_BUS_LISTENER_METHOD 0x0002
#define MESSAGE_BUS_LISTENER_REENTRANT 0x0004
#define MESSAGE_BUS_LISTENER_BUSY 0x0008
struct MicroBitListener
{
uint16_t id; // The ID of the component that this listener is interested in.
uint16_t value; // Value this listener is interested in receiving.
uint16_t flags; // Status and configuration options codes for this listener.
union
{
void (*cb)(MicroBitEvent);
void (*cb_param)(MicroBitEvent, void *);
MemberFunctionCallback *cb_method;
};
void* cb_arg; // Optional argument to be passed to the caller.
MicroBitEvent evt;
MicroBitListener *next;
/**
* Constructor.
* Create a new Message Bus Listener.
* @param id The ID of the component you want to listen to.
* @param value The event ID you would like to listen to from that component
* @param handler A function pointer to call when the event is detected.
*/
MicroBitListener(uint16_t id, uint16_t value, void (*handler)(MicroBitEvent));
/**
* Alternative constructor where we register a value to be passed to the
* callback.
*/
MicroBitListener(uint16_t id, uint16_t value, void (*handler)(MicroBitEvent, void *), void* arg);
/**
* Constructor.
* Create a new Message Bus Listener, with a callback to a c++ member function.
* @param id The ID of the component you want to listen to.
* @param value The event ID you would like to listen to from that component.
* @param object The C++ object on which to call the event handler.
* @param object The method within the C++ object to call.
*/
template <typename T>
MicroBitListener(uint16_t id, uint16_t value, T* object, void (T::*method)(MicroBitEvent));
};
/**
* Constructor.
* Create a new Message Bus Listener, with a callback to a c++ member function.
* @param id The ID of the component you want to listen to.
* @param value The event ID you would like to listen to from that component.
* @param object The C++ object on which to call the event handler.
* @param object The method within the C++ object to call.
*/
template <typename T>
MicroBitListener::MicroBitListener(uint16_t id, uint16_t value, T* object, void (T::*method)(MicroBitEvent))
{
this->id = id;
this->value = value;
this->cb_method = new MemberFunctionCallback(object, method);
this->cb_arg = NULL;
this->flags = MESSAGE_BUS_LISTENER_METHOD;
this->next = NULL;
}
#endif

82
inc/MicroBitMessageBus.h
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@ -2,6 +2,8 @@
#define MICROBIT_MESSAGE_BUS_H
#include "mbed.h"
#include "MemberFunctionCallback.h"
#include "MicroBitListener.h"
#include "MicroBitComponent.h"
#include "MicroBitEvent.h"
@ -10,33 +12,9 @@
#define MICROBIT_ID_ANY 0
#define MICROBIT_EVT_ANY 0
struct MicroBitListener
{
uint16_t id; // The ID of the component that this listener is interested in.
uint16_t value; // Value this listener is interested in receiving.
void* cb; // Callback function associated with this listener. Either (*cb)(MicroBitEvent) or (*cb)(MicroBitEvent, void*) depending on whether cb_arg is NULL.
void* cb_arg; // Argument to be passed to the caller. This is assumed to be a pointer, so passing in NULL means that the function doesn't take an argument.
MicroBitEvent evt;
MicroBitListener *next;
/**
* Constructor.
* Create a new Message Bus Listener.
* @param id The ID of the component you want to listen to.
* @param value The event ID you would like to listen to from that component
* @param handler A function pointer to call when the event is detected.
*/
MicroBitListener(uint16_t id, uint16_t value, void (*handler)(MicroBitEvent));
/**
* Alternative constructor where we register a value to be passed to the
* callback. If arg == NULL, the function takes no extra arguemnt.
* Otherwise, the function is understood to take an extra argument.
*/
MicroBitListener(uint16_t id, uint16_t value, void *handler, void* arg);
};
/**
* Enclosing class to hold a chain of events.
*/
struct MicroBitEventQueueItem
{
MicroBitEvent evt;
@ -50,6 +28,7 @@ struct MicroBitEventQueueItem
MicroBitEventQueueItem(MicroBitEvent evt);
};
/**
* Class definition for the MicroBitMessageBus.
*
@ -136,14 +115,28 @@ class MicroBitMessageBus : public MicroBitComponent
*/
void listen(int id, int value, void (*handler)(MicroBitEvent, void*), void* arg);
/**
* Register a listener function.
*
* As above, but allows callbacks into member functions within a C++ object.
* This one is a bit more complex, but hey, that's C++ for you!
*/
template <typename T>
void listen(uint16_t id, uint16_t value, T* object, void (T::*handler)(MicroBitEvent));
private:
/**
* Add the given MicroBitListener to the list of event handlers, unconditionally.
* @param listener The MicroBitListener to validate.
* @return 1 if the listener is valid, 0 otherwise.
*/
int add(MicroBitListener *newListener);
MicroBitListener *listeners; // Chain of active listeners.
MicroBitEventQueueItem *evt_queue_head; // Head of queued events to be processed.
MicroBitEventQueueItem *evt_queue_tail; // Tail of queued events to be processed.
int seq; // Sequence number. Used to invalidate cache entries.
void listen(int id, int value, void* handler, void* arg);
void queueEvent(MicroBitEvent &evt);
MicroBitEventQueueItem* dequeueEvent();
@ -151,6 +144,35 @@ class MicroBitMessageBus : public MicroBitComponent
virtual int isIdleCallbackNeeded();
};
/**
* A registrationt function to allow C++ member funcitons (methods) to be registered as an event
* listener.
*
* @param id The source of messages to listen for. Events sent from any other IDs will be filtered.
* Use MICROBIT_ID_ANY to receive events from all components.
*
* @param value The value of messages to listen for. Events with any other values will be filtered.
* Use MICROBIT_EVT_ANY to receive events of any value.
*
* @param object The object on which the method should be invoked.
* @param hander The method to call when an event is received.
*/
template <typename T>
void MicroBitMessageBus::listen(uint16_t id, uint16_t value, T* object, void (T::*handler)(MicroBitEvent))
{
if (object == NULL || handler == NULL)
return;
MicroBitListener *newListener = new MicroBitListener(id, value, object, handler);
if(!add(newListener))
{
delete newListener->cb_method;
delete newListener;
return;
}
}
#endif

2
source/CMakeLists.txt
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@ -28,6 +28,8 @@ set(YOTTA_AUTO_MICROBIT-DAL_CPP_FILES
"MicroBitPin.cpp"
"MicroBitSerial.cpp"
"MicroBitHeapAllocator.cpp"
"MicroBitListener.cpp"
"MemberFunctionCallback.cpp"
)
if (YOTTA_CFG_MICROBIT_CONFIGFILE)

32
source/MemberFunctionCallback.cpp Normal file
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@ -0,0 +1,32 @@
/**
* Class definition for a MemberFunctionCallback.
*
* C++ member functions (also known as methods) have a more complex
* representation than normal C functions. This allows a referene to
* a C++ member function to be stored then called at a later date.
*
* This class is used extensively by the MicroBitMessageBus to deliver
* events to C++ methods.
*/
#include "MicroBit.h"
/**
* Calls the method reference held by this MemberFunctionCallback.
* @param e The event to deliver to the method
*/
void MemberFunctionCallback::fire(MicroBitEvent e)
{
invoke(object, method, e);
}
/**
* Comparison of two MemberFunctionCallback objects.
* @return TRUE if the given MemberFunctionCallback is equivalent to this one. FALSE otherwise.
*/
bool MemberFunctionCallback::operator==(const MemberFunctionCallback &mfc)
{
return (object == mfc.object && memcmp(method,mfc.method,sizeof(method))==0);
}

45
source/MicroBitListener.cpp Normal file
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@ -0,0 +1,45 @@
/**
* Class definition for a MicroBitListener.
*
* MicroBitListener holds all the information related to a single event handler required
* to match and fire event handlers to incoming events.
*/
#include "mbed.h"
#include "MicroBit.h"
/**
* Constructor.
* Create a new Message Bus Listener.
* @param id The ID of the component you want to listen to.
* @param value The event ID you would like to listen to from that component
* @param handler A function pointer to call when the event is detected.
*/
MicroBitListener::MicroBitListener(uint16_t id, uint16_t value, void (*handler)(MicroBitEvent))
{
this->id = id;
this->value = value;
this->cb = handler;
this->cb_arg = NULL;
this->flags = 0;
this->next = NULL;
}
/**
* Constructor.
* Create a new parameterised Message Bus Listener.
* @param id The ID of the component you want to listen to.
* @param value The event ID you would like to listen to from that component.
* @param handler A function pointer to call when the event is detected.
* @param arg An additional argument to pass to the event handler function.
*/
MicroBitListener::MicroBitListener(uint16_t id, uint16_t value, void (*handler)(MicroBitEvent, void *), void* arg)
{
this->id = id;
this->value = value;
this->cb_param = handler;
this->cb_arg = arg;
this->flags = MESSAGE_BUS_LISTENER_PARAMETERISED;
this->next = NULL;
}

131
source/MicroBitMessageBus.cpp
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@ -16,34 +16,7 @@ MicroBitEventQueueItem::MicroBitEventQueueItem(MicroBitEvent evt)
this->evt = evt;
this->next = NULL;
}
/**
* Constructor.
* Create a new Message Bus Listener.
* @param id The ID of the component you want to listen to.
* @param value The event ID you would like to listen to from that component
* @param handler A function pointer to call when the event is detected.
*/
MicroBitListener::MicroBitListener(uint16_t id, uint16_t value, void (*handler)(MicroBitEvent))
{
this->id = id;
this->value = value;
this->cb = (void*) handler;
this->cb_arg = NULL;
this->next = NULL;
}
/**
* A low-level, internal version of the constructor, where the handler's type is determined
* by the value of arg. (See MicroBitMessageBus.h).
*/
MicroBitListener::MicroBitListener(uint16_t id, uint16_t value, void* handler, void* arg)
{
this->id = id;
this->value = value;
this->cb = handler;
this->cb_arg = arg;
this->next = NULL;
}
/**
* Constructor.
@ -65,10 +38,21 @@ MicroBitMessageBus::MicroBitMessageBus()
void async_callback(void *param)
{
MicroBitListener *listener = (MicroBitListener *)param;
if (listener->cb_arg != NULL)
((void (*)(MicroBitEvent, void*))listener->cb)(listener->evt, listener->cb_arg);
// Determine the calling convention for the callback, and invoke...
// C++ is really bad at this! Especially as the ARM compiler is yet to support C++ 11 :-/
// Firstly, check for a method callback into an object.
if (listener->flags & MESSAGE_BUS_LISTENER_METHOD)
listener->cb_method->fire(listener->evt);
// Now a parameterised C function
else if (listener->flags & MESSAGE_BUS_LISTENER_PARAMETERISED)
listener->cb_param(listener->evt, listener->cb_arg);
// We must have a plain C function
else
((void (*)(MicroBitEvent))listener->cb)(listener->evt);
listener->cb(listener->evt);
}
@ -243,8 +227,6 @@ void MicroBitMessageBus::process(MicroBitEvent evt)
*
* @param hander The function to call when an event is received.
*
* TODO: We currently don't support C++ member functions as callbacks, which we should.
*
* Example:
* @code
* void onButtonBClick(MicroBitEvent evt)
@ -255,75 +237,110 @@ void MicroBitMessageBus::process(MicroBitEvent evt)
* @endcode
*/
void MicroBitMessageBus::listen(int id, int value, void (*handler)(MicroBitEvent, void*), void* arg) {
this->listen(id, value, (void*) handler, arg);
}
void MicroBitMessageBus::listen(int id, int value, void (*handler)(MicroBitEvent)) {
this->listen(id, value, (void*) handler, NULL);
}
void MicroBitMessageBus::listen(int id, int value, void* handler, void* arg)
void MicroBitMessageBus::listen(int id, int value, void (*handler)(MicroBitEvent))
{
//handler can't be NULL!
if (handler == NULL)
return;
MicroBitListener *newListener = new MicroBitListener(id, value, handler);
if(!add(newListener))
{
delete newListener;
return;
}
}
void MicroBitMessageBus::listen(int id, int value, void (*handler)(MicroBitEvent, void*), void* arg)
{
if (handler == NULL)
return;
MicroBitListener *newListener = new MicroBitListener(id, value, handler, arg);
if(!add(newListener))
{
delete newListener;
return;
}
}
/**
* Add the given MicroBitListener to the list of event handlers, unconditionally.
* @param listener The MicroBitListener to validate.
* @return 1 if the listener is valid, 0 otherwise.
*/
int MicroBitMessageBus::add(MicroBitListener *newListener)
{
MicroBitListener *l, *p;
int methodCallback;
//handler can't be NULL!
if (newListener == NULL)
return 0;
methodCallback = newListener->flags & MESSAGE_BUS_LISTENER_METHOD;
l = listeners;
// Firstly, we treat a listener as an idempotent operation. Ensure we don't already have this handler
// registered in a that will already capture these events. If we do, silently ignore.
while (l != NULL)
{
if (l->id == id && l->value == value && l->cb == handler)
return;
l = l->next;
}
// We always check the ID, VALUE and CB_METHOD fields.
// If we have a callback to a method, check the cb_method class. Otherwise, the cb function point is sufficient.
while (l != NULL)
{
if (l->id == newListener->id && l->value == newListener->value && (methodCallback ? *l->cb_method == *newListener->cb_method : l->cb == newListener->cb))
return 0;
MicroBitListener *newListener = new MicroBitListener(id, value, handler, arg);
l = l->next;
}
//if listeners is null - we can automatically add this listener to the list at the beginning...
// We have a valid, new event handler. Add it to the list.
// if listeners is null - we can automatically add this listener to the list at the beginning...
if (listeners == NULL)
{
listeners = newListener;
return;
return 1;
}
// Maintain an ordered list of listeners.
// Chain is held stictly in increasing order of ID (first level), then value code (second level).
// We maintain an ordered list of listeners.
// The chain is held stictly in increasing order of ID (first level), then value code (second level).
// Find the correct point in the chain for this event.
// Adding a listener is a rare occurance, so we just walk the list.
// Adding a listener is a rare occurance, so we just walk the list...
p = listeners;
l = listeners;
while (l != NULL && l->id < id)
while (l != NULL && l->id < newListener->id)
{
p = l;
l = l->next;
}
while (l != NULL && l->id == id && l->value < value)
while (l != NULL && l->id == newListener->id && l->value < newListener->value)
{
p = l;
l = l->next;
}
//add at front of list
if (p == listeners && (id < p->id || (p->id == id && p->value > value)))
if (p == listeners && (newListener->id < p->id || (p->id == newListener->id && p->value > newListener->value)))
{
newListener->next = p;
//this new listener is now the front!
listeners = newListener;
}
//add after p
else
{
newListener->next = p->next;
p->next = newListener;
}
return 1;
}