Knight KE / Mbed OS Game_Master

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mbed-os/events/README.md@0:9b3d4731edbb, 2018-06-21 (annotated)

Committer:
WFKnight
Date:
Thu Jun 21 13:51:43 2018 +0000
Revision:
0:9b3d4731edbb
UART, RTOS, LED

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WFKnight 0:9b3d4731edbb 1 ## The mbed-events library ##
WFKnight 0:9b3d4731edbb 2
WFKnight 0:9b3d4731edbb 3 The mbed-events library provides a flexible queue for scheduling events.
WFKnight 0:9b3d4731edbb 4
WFKnight 0:9b3d4731edbb 5 ``` cpp
WFKnight 0:9b3d4731edbb 6 #include "mbed_events.h"
WFKnight 0:9b3d4731edbb 7 #include <stdio.h>
WFKnight 0:9b3d4731edbb 8
WFKnight 0:9b3d4731edbb 9 int main() {
WFKnight 0:9b3d4731edbb 10 // creates a queue with the default size
WFKnight 0:9b3d4731edbb 11 EventQueue queue;
WFKnight 0:9b3d4731edbb 12
WFKnight 0:9b3d4731edbb 13 // events are simple callbacks
WFKnight 0:9b3d4731edbb 14 queue.call(printf, "called immediately\n");
WFKnight 0:9b3d4731edbb 15 queue.call_in(2000, printf, "called in 2 seconds\n");
WFKnight 0:9b3d4731edbb 16 queue.call_every(1000, printf, "called every 1 seconds\n");
WFKnight 0:9b3d4731edbb 17
WFKnight 0:9b3d4731edbb 18 // events are executed by the dispatch method
WFKnight 0:9b3d4731edbb 19 queue.dispatch();
WFKnight 0:9b3d4731edbb 20 }
WFKnight 0:9b3d4731edbb 21 ```
WFKnight 0:9b3d4731edbb 22
WFKnight 0:9b3d4731edbb 23 The mbed-events library can be used as a normal event loop, or it can be
WFKnight 0:9b3d4731edbb 24 backgrounded on a single hardware timer or even another event loop. It is
WFKnight 0:9b3d4731edbb 25 both thread and irq safe, and provides functions for easily composing
WFKnight 0:9b3d4731edbb 26 independent event queues.
WFKnight 0:9b3d4731edbb 27
WFKnight 0:9b3d4731edbb 28 The mbed-events library can act as a drop-in scheduler, provide synchronization
WFKnight 0:9b3d4731edbb 29 between multiple threads, or just act as a mechanism for moving events out of
WFKnight 0:9b3d4731edbb 30 interrupt contexts.
WFKnight 0:9b3d4731edbb 31
WFKnight 0:9b3d4731edbb 32 ### Usage ###
WFKnight 0:9b3d4731edbb 33
WFKnight 0:9b3d4731edbb 34 The core of the mbed-events library is the [EventQueue](EventQueue.h) class,
WFKnight 0:9b3d4731edbb 35 which represents a single event queue. The `EventQueue::dispatch` function
WFKnight 0:9b3d4731edbb 36 runs the queue, providing the context for executing events.
WFKnight 0:9b3d4731edbb 37
WFKnight 0:9b3d4731edbb 38 ``` cpp
WFKnight 0:9b3d4731edbb 39 // Creates an event queue enough buffer space for 32 Callbacks. This
WFKnight 0:9b3d4731edbb 40 // is the default if no argument was provided. Alternatively the size
WFKnight 0:9b3d4731edbb 41 // can just be specified in bytes.
WFKnight 0:9b3d4731edbb 42 EventQueue queue(32*EVENTS_EVENT_SIZE);
WFKnight 0:9b3d4731edbb 43
WFKnight 0:9b3d4731edbb 44 // Events can be posted to the underlying event queue with dynamic
WFKnight 0:9b3d4731edbb 45 // context allocated from the specified buffer
WFKnight 0:9b3d4731edbb 46 queue.call(printf, "hello %d %d %d %d\n", 1, 2, 3, 4);
WFKnight 0:9b3d4731edbb 47 queue.call(&serial, &Serial::printf, "hi\n");
WFKnight 0:9b3d4731edbb 48
WFKnight 0:9b3d4731edbb 49 // The dispatch function provides the context for the running the queue
WFKnight 0:9b3d4731edbb 50 // and can take a millisecond timeout to run for a fixed time or to just
WFKnight 0:9b3d4731edbb 51 // dispatch any pending events
WFKnight 0:9b3d4731edbb 52 queue.dispatch();
WFKnight 0:9b3d4731edbb 53 ```
WFKnight 0:9b3d4731edbb 54
WFKnight 0:9b3d4731edbb 55 The EventQueue class provides several call functions for posting events
WFKnight 0:9b3d4731edbb 56 to the underlying event queue. The call functions are thread and irq safe,
WFKnight 0:9b3d4731edbb 57 don't need the underlying loop to be running, and provide an easy mechanism
WFKnight 0:9b3d4731edbb 58 for moving events out of interrupt contexts.
WFKnight 0:9b3d4731edbb 59
WFKnight 0:9b3d4731edbb 60 ``` cpp
WFKnight 0:9b3d4731edbb 61 // Simple call function registers events to be called as soon as possible
WFKnight 0:9b3d4731edbb 62 queue.call(doit);
WFKnight 0:9b3d4731edbb 63 queue.call(printf, "called immediately\n");
WFKnight 0:9b3d4731edbb 64
WFKnight 0:9b3d4731edbb 65 // The call_in function registers events to be called after a delay
WFKnight 0:9b3d4731edbb 66 // specified in milliseconds
WFKnight 0:9b3d4731edbb 67 queue.call_in(2000, doit_in_two_seconds);
WFKnight 0:9b3d4731edbb 68 queue.call_in(300, printf, "called in 0.3 seconds\n");
WFKnight 0:9b3d4731edbb 69
WFKnight 0:9b3d4731edbb 70 // The call_every function registers events to be called repeatedly
WFKnight 0:9b3d4731edbb 71 // with a period specified in milliseconds
WFKnight 0:9b3d4731edbb 72 queue.call_every(2000, doit_every_two_seconds);
WFKnight 0:9b3d4731edbb 73 queue.call_every(400, printf, "called every 0.4 seconds\n");
WFKnight 0:9b3d4731edbb 74 ```
WFKnight 0:9b3d4731edbb 75
WFKnight 0:9b3d4731edbb 76 The call functions return an id that uniquely represents the event in the
WFKnight 0:9b3d4731edbb 77 the event queue. This id can be passed to `EventQueue::cancel` to cancel
WFKnight 0:9b3d4731edbb 78 an in-flight event.
WFKnight 0:9b3d4731edbb 79
WFKnight 0:9b3d4731edbb 80 ``` cpp
WFKnight 0:9b3d4731edbb 81 // The event id uniquely represents the event in the queue
WFKnight 0:9b3d4731edbb 82 int id = queue.call_in(100, printf, "will this work?\n");
WFKnight 0:9b3d4731edbb 83
WFKnight 0:9b3d4731edbb 84 // If there was not enough memory necessary to allocate the event,
WFKnight 0:9b3d4731edbb 85 // an id of 0 is returned from the call functions
WFKnight 0:9b3d4731edbb 86 if (id) {
WFKnight 0:9b3d4731edbb 87 error("oh no!");
WFKnight 0:9b3d4731edbb 88 }
WFKnight 0:9b3d4731edbb 89
WFKnight 0:9b3d4731edbb 90 // Events can be cancelled as long as they have not been dispatched. If the
WFKnight 0:9b3d4731edbb 91 // event has already expired, cancel has no side-effects.
WFKnight 0:9b3d4731edbb 92 queue.cancel(id);
WFKnight 0:9b3d4731edbb 93 ```
WFKnight 0:9b3d4731edbb 94
WFKnight 0:9b3d4731edbb 95 For a more fine-grain control of event dispatch, the `Event` class can be
WFKnight 0:9b3d4731edbb 96 manually instantiated and configured. An `Event` represents an event as
WFKnight 0:9b3d4731edbb 97 a C++ style function object and can be directly passed to other APIs that
WFKnight 0:9b3d4731edbb 98 expect a callback.
WFKnight 0:9b3d4731edbb 99
WFKnight 0:9b3d4731edbb 100 ``` cpp
WFKnight 0:9b3d4731edbb 101 // Creates an event bound to the specified event queue
WFKnight 0:9b3d4731edbb 102 EventQueue queue;
WFKnight 0:9b3d4731edbb 103 Event<void()> event(&queue, doit);
WFKnight 0:9b3d4731edbb 104
WFKnight 0:9b3d4731edbb 105 // The event can be manually configured for special timing requirements
WFKnight 0:9b3d4731edbb 106 // specified in milliseconds
WFKnight 0:9b3d4731edbb 107 event.delay(10);
WFKnight 0:9b3d4731edbb 108 event.period(10000);
WFKnight 0:9b3d4731edbb 109
WFKnight 0:9b3d4731edbb 110 // Posted events are dispatched in the context of the queue's
WFKnight 0:9b3d4731edbb 111 // dispatch function
WFKnight 0:9b3d4731edbb 112 queue.dispatch();
WFKnight 0:9b3d4731edbb 113
WFKnight 0:9b3d4731edbb 114 // Events can also pass arguments to the underlying callback when both
WFKnight 0:9b3d4731edbb 115 // initially constructed and posted.
WFKnight 0:9b3d4731edbb 116 Event<void(int, int)> event(&queue, printf, "received %d and %d\n");
WFKnight 0:9b3d4731edbb 117
WFKnight 0:9b3d4731edbb 118 // Events can be posted multiple times and enqueue gracefully until
WFKnight 0:9b3d4731edbb 119 // the dispatch function is called.
WFKnight 0:9b3d4731edbb 120 event.post(1, 2);
WFKnight 0:9b3d4731edbb 121 event.post(3, 4);
WFKnight 0:9b3d4731edbb 122 event.post(5, 6);
WFKnight 0:9b3d4731edbb 123
WFKnight 0:9b3d4731edbb 124 queue.dispatch();
WFKnight 0:9b3d4731edbb 125 ```
WFKnight 0:9b3d4731edbb 126
WFKnight 0:9b3d4731edbb 127 Event queues easily align with module boundaries, where internal state can
WFKnight 0:9b3d4731edbb 128 be implicitly synchronized through event dispatch. Multiple modules can
WFKnight 0:9b3d4731edbb 129 use independent event queues, but still be composed through the
WFKnight 0:9b3d4731edbb 130 `EventQueue::chain` function.
WFKnight 0:9b3d4731edbb 131
WFKnight 0:9b3d4731edbb 132 ``` cpp
WFKnight 0:9b3d4731edbb 133 // Create some event queues with pending events
WFKnight 0:9b3d4731edbb 134 EventQueue a;
WFKnight 0:9b3d4731edbb 135 a.call(printf, "hello from a!\n");
WFKnight 0:9b3d4731edbb 136
WFKnight 0:9b3d4731edbb 137 EventQueue b;
WFKnight 0:9b3d4731edbb 138 b.call(printf, "hello from b!\n");
WFKnight 0:9b3d4731edbb 139
WFKnight 0:9b3d4731edbb 140 EventQueue c;
WFKnight 0:9b3d4731edbb 141 c.call(printf, "hello from c!\n");
WFKnight 0:9b3d4731edbb 142
WFKnight 0:9b3d4731edbb 143 // Chain c and b onto a's event queue. Both c and b will be dispatched
WFKnight 0:9b3d4731edbb 144 // in the context of a's dispatch function.
WFKnight 0:9b3d4731edbb 145 c.chain(&a);
WFKnight 0:9b3d4731edbb 146 b.chain(&a);
WFKnight 0:9b3d4731edbb 147
WFKnight 0:9b3d4731edbb 148 // Dispatching a will in turn dispatch b and c, printing hello from
WFKnight 0:9b3d4731edbb 149 // all three queues
WFKnight 0:9b3d4731edbb 150 a.dispatch();
WFKnight 0:9b3d4731edbb 151 ```
WFKnight 0:9b3d4731edbb 152
WFKnight 0:9b3d4731edbb 153