ST / ST_Events-old

This is a fork of the `events` subdirectory of https://github.com/ARMmbed/mbed-os

Dependents:   HelloWorld_CCA01M1 HelloWorld_CCA02M1 CI-data-logger-server HelloWorld_CCA02M1 ... more

This is a fork of the events subdirectory of https://github.com/ARMmbed/mbed-os.

Note, you must import this library with import name: events!!!

README.md@9832:b95afde9ef7e, 2017-09-05 (annotated)

Committer:
Wolfgang Betz
Date:
Tue Sep 05 09:09:24 2017 +0200
Revision:
9832:b95afde9ef7e
Parent:
0:a792d4bf36c2 
Merge branch 'master' of hg::http://developer.mbed.org/teams/ST/code/ST_Events into events-split

Who changed what in which revision?

UserRevisionLine numberNew contents of line
Bogdan Marinescu 0:a792d4bf36c2 1 ## The mbed-events library ##
Bogdan Marinescu 0:a792d4bf36c2 2
Bogdan Marinescu 0:a792d4bf36c2 3 The mbed-events library provides a flexible queue for scheduling events.
Bogdan Marinescu 0:a792d4bf36c2 4
Bogdan Marinescu 0:a792d4bf36c2 5 ``` cpp
Bogdan Marinescu 0:a792d4bf36c2 6 #include "mbed_events.h"
Bogdan Marinescu 0:a792d4bf36c2 7 #include <stdio.h>
Bogdan Marinescu 0:a792d4bf36c2 8
Bogdan Marinescu 0:a792d4bf36c2 9 int main() {
Bogdan Marinescu 0:a792d4bf36c2 10 // creates a queue with the default size
Bogdan Marinescu 0:a792d4bf36c2 11 EventQueue queue;
Bogdan Marinescu 0:a792d4bf36c2 12
Bogdan Marinescu 0:a792d4bf36c2 13 // events are simple callbacks
Bogdan Marinescu 0:a792d4bf36c2 14 queue.call(printf, "called immediately\n");
Bogdan Marinescu 0:a792d4bf36c2 15 queue.call_in(2000, printf, "called in 2 seconds\n");
Bogdan Marinescu 0:a792d4bf36c2 16 queue.call_every(1000, printf, "called every 1 seconds\n");
Bogdan Marinescu 0:a792d4bf36c2 17
Bogdan Marinescu 0:a792d4bf36c2 18 // events are executed by the dispatch method
Bogdan Marinescu 0:a792d4bf36c2 19 queue.dispatch();
Bogdan Marinescu 0:a792d4bf36c2 20 }
Bogdan Marinescu 0:a792d4bf36c2 21 ```
Bogdan Marinescu 0:a792d4bf36c2 22
Bogdan Marinescu 0:a792d4bf36c2 23 The mbed-events library can be used as a normal event loop, or it can be
Bogdan Marinescu 0:a792d4bf36c2 24 backgrounded on a single hardware timer or even another event loop. It is
Bogdan Marinescu 0:a792d4bf36c2 25 both thread and irq safe, and provides functions for easily composing
Bogdan Marinescu 0:a792d4bf36c2 26 independent event queues.
Bogdan Marinescu 0:a792d4bf36c2 27
Bogdan Marinescu 0:a792d4bf36c2 28 The mbed-events library can act as a drop-in scheduler, provide synchronization
Bogdan Marinescu 0:a792d4bf36c2 29 between multiple threads, or just act as a mechanism for moving events out of
Bogdan Marinescu 0:a792d4bf36c2 30 interrupt contexts.
Bogdan Marinescu 0:a792d4bf36c2 31
Bogdan Marinescu 0:a792d4bf36c2 32 ### Usage ###
Bogdan Marinescu 0:a792d4bf36c2 33
Bogdan Marinescu 0:a792d4bf36c2 34 The core of the mbed-events library is the [EventQueue](EventQueue.h) class,
Bogdan Marinescu 0:a792d4bf36c2 35 which represents a single event queue. The `EventQueue::dispatch` function
Bogdan Marinescu 0:a792d4bf36c2 36 runs the queue, providing the context for executing events.
Bogdan Marinescu 0:a792d4bf36c2 37
Bogdan Marinescu 0:a792d4bf36c2 38 ``` cpp
Bogdan Marinescu 0:a792d4bf36c2 39 // Creates an event queue enough buffer space for 32 Callbacks. This
Bogdan Marinescu 0:a792d4bf36c2 40 // is the default if no argument was provided. Alternatively the size
Bogdan Marinescu 0:a792d4bf36c2 41 // can just be specified in bytes.
Bogdan Marinescu 0:a792d4bf36c2 42 EventQueue queue(32*EVENTS_EVENT_SIZE);
Bogdan Marinescu 0:a792d4bf36c2 43
Bogdan Marinescu 0:a792d4bf36c2 44 // Events can be posted to the underlying event queue with dynamic
Bogdan Marinescu 0:a792d4bf36c2 45 // context allocated from the specified buffer
Bogdan Marinescu 0:a792d4bf36c2 46 queue.call(printf, "hello %d %d %d %d\n", 1, 2, 3, 4);
Bogdan Marinescu 0:a792d4bf36c2 47 queue.call(&serial, &Serial::printf, "hi\n");
Bogdan Marinescu 0:a792d4bf36c2 48
Bogdan Marinescu 0:a792d4bf36c2 49 // The dispatch function provides the context for the running the queue
Bogdan Marinescu 0:a792d4bf36c2 50 // and can take a millisecond timeout to run for a fixed time or to just
Bogdan Marinescu 0:a792d4bf36c2 51 // dispatch any pending events
Bogdan Marinescu 0:a792d4bf36c2 52 queue.dispatch();
Bogdan Marinescu 0:a792d4bf36c2 53 ```
Bogdan Marinescu 0:a792d4bf36c2 54
Bogdan Marinescu 0:a792d4bf36c2 55 The EventQueue class provides several call functions for posting events
Bogdan Marinescu 0:a792d4bf36c2 56 to the underlying event queue. The call functions are thread and irq safe,
Bogdan Marinescu 0:a792d4bf36c2 57 don't need the underlying loop to be running, and provide an easy mechanism
Bogdan Marinescu 0:a792d4bf36c2 58 for moving events out of interrupt contexts.
Bogdan Marinescu 0:a792d4bf36c2 59
Bogdan Marinescu 0:a792d4bf36c2 60 ``` cpp
Bogdan Marinescu 0:a792d4bf36c2 61 // Simple call function registers events to be called as soon as possible
Bogdan Marinescu 0:a792d4bf36c2 62 queue.call(doit);
Bogdan Marinescu 0:a792d4bf36c2 63 queue.call(printf, "called immediately\n");
Bogdan Marinescu 0:a792d4bf36c2 64
Bogdan Marinescu 0:a792d4bf36c2 65 // The call_in function registers events to be called after a delay
Bogdan Marinescu 0:a792d4bf36c2 66 // specified in milliseconds
Bogdan Marinescu 0:a792d4bf36c2 67 queue.call_in(2000, doit_in_two_seconds);
Bogdan Marinescu 0:a792d4bf36c2 68 queue.call_in(300, printf, "called in 0.3 seconds\n");
Bogdan Marinescu 0:a792d4bf36c2 69
Bogdan Marinescu 0:a792d4bf36c2 70 // The call_every function registers events to be called repeatedly
Bogdan Marinescu 0:a792d4bf36c2 71 // with a period specified in milliseconds
Bogdan Marinescu 0:a792d4bf36c2 72 queue.call_every(2000, doit_every_two_seconds);
Bogdan Marinescu 0:a792d4bf36c2 73 queue.call_every(400, printf, "called every 0.4 seconds\n");
Bogdan Marinescu 0:a792d4bf36c2 74 ```
Bogdan Marinescu 0:a792d4bf36c2 75
Bogdan Marinescu 0:a792d4bf36c2 76 The call functions return an id that uniquely represents the event in the
Bogdan Marinescu 0:a792d4bf36c2 77 the event queue. This id can be passed to `EventQueue::cancel` to cancel
Bogdan Marinescu 0:a792d4bf36c2 78 an in-flight event.
Bogdan Marinescu 0:a792d4bf36c2 79
Bogdan Marinescu 0:a792d4bf36c2 80 ``` cpp
Bogdan Marinescu 0:a792d4bf36c2 81 // The event id uniquely represents the event in the queue
Bogdan Marinescu 0:a792d4bf36c2 82 int id = queue.call_in(100, printf, "will this work?\n");
Bogdan Marinescu 0:a792d4bf36c2 83
Bogdan Marinescu 0:a792d4bf36c2 84 // If there was not enough memory necessary to allocate the event,
Bogdan Marinescu 0:a792d4bf36c2 85 // an id of 0 is returned from the call functions
Bogdan Marinescu 0:a792d4bf36c2 86 if (id) {
Bogdan Marinescu 0:a792d4bf36c2 87 error("oh no!");
Bogdan Marinescu 0:a792d4bf36c2 88 }
Bogdan Marinescu 0:a792d4bf36c2 89
Bogdan Marinescu 0:a792d4bf36c2 90 // Events can be cancelled as long as they have not been dispatched. If the
Bogdan Marinescu 0:a792d4bf36c2 91 // event has already expired, cancel has no side-effects.
Bogdan Marinescu 0:a792d4bf36c2 92 queue.cancel(id);
Bogdan Marinescu 0:a792d4bf36c2 93 ```
Bogdan Marinescu 0:a792d4bf36c2 94
Bogdan Marinescu 0:a792d4bf36c2 95 For a more fine-grain control of event dispatch, the `Event` class can be
Bogdan Marinescu 0:a792d4bf36c2 96 manually instantiated and configured. An `Event` represents an event as
Bogdan Marinescu 0:a792d4bf36c2 97 a C++ style function object and can be directly passed to other APIs that
Bogdan Marinescu 0:a792d4bf36c2 98 expect a callback.
Bogdan Marinescu 0:a792d4bf36c2 99
Bogdan Marinescu 0:a792d4bf36c2 100 ``` cpp
Bogdan Marinescu 0:a792d4bf36c2 101 // Creates an event bound to the specified event queue
Bogdan Marinescu 0:a792d4bf36c2 102 EventQueue queue;
Bogdan Marinescu 0:a792d4bf36c2 103 Event<void()> event(&queue, doit);
Bogdan Marinescu 0:a792d4bf36c2 104
Bogdan Marinescu 0:a792d4bf36c2 105 // The event can be manually configured for special timing requirements
Bogdan Marinescu 0:a792d4bf36c2 106 // specified in milliseconds
Bogdan Marinescu 0:a792d4bf36c2 107 event.delay(10);
Bogdan Marinescu 0:a792d4bf36c2 108 event.period(10000);
Bogdan Marinescu 0:a792d4bf36c2 109
Bogdan Marinescu 0:a792d4bf36c2 110 // Posted events are dispatched in the context of the queue's
Bogdan Marinescu 0:a792d4bf36c2 111 // dispatch function
Bogdan Marinescu 0:a792d4bf36c2 112 queue.dispatch();
Bogdan Marinescu 0:a792d4bf36c2 113
Bogdan Marinescu 0:a792d4bf36c2 114 // Events can also pass arguments to the underlying callback when both
Bogdan Marinescu 0:a792d4bf36c2 115 // initially constructed and posted.
Bogdan Marinescu 0:a792d4bf36c2 116 Event<void(int, int)> event(&queue, printf, "recieved %d and %d\n");
Bogdan Marinescu 0:a792d4bf36c2 117
Bogdan Marinescu 0:a792d4bf36c2 118 // Events can be posted multiple times and enqueue gracefully until
Bogdan Marinescu 0:a792d4bf36c2 119 // the dispatch function is called.
Bogdan Marinescu 0:a792d4bf36c2 120 event.post(1, 2);
Bogdan Marinescu 0:a792d4bf36c2 121 event.post(3, 4);
Bogdan Marinescu 0:a792d4bf36c2 122 event.post(5, 6);
Bogdan Marinescu 0:a792d4bf36c2 123
Bogdan Marinescu 0:a792d4bf36c2 124 queue.dispatch();
Bogdan Marinescu 0:a792d4bf36c2 125 ```
Bogdan Marinescu 0:a792d4bf36c2 126
Bogdan Marinescu 0:a792d4bf36c2 127 Event queues easily align with module boundaries, where internal state can
Bogdan Marinescu 0:a792d4bf36c2 128 be implicitly synchronized through event dispatch. Multiple modules can
Bogdan Marinescu 0:a792d4bf36c2 129 use independent event queues, but still be composed through the
Bogdan Marinescu 0:a792d4bf36c2 130 `EventQueue::chain` function.
Bogdan Marinescu 0:a792d4bf36c2 131
Bogdan Marinescu 0:a792d4bf36c2 132 ``` cpp
Bogdan Marinescu 0:a792d4bf36c2 133 // Create some event queues with pending events
Bogdan Marinescu 0:a792d4bf36c2 134 EventQueue a;
Bogdan Marinescu 0:a792d4bf36c2 135 a.call(printf, "hello from a!\n");
Bogdan Marinescu 0:a792d4bf36c2 136
Bogdan Marinescu 0:a792d4bf36c2 137 EventQueue b;
Bogdan Marinescu 0:a792d4bf36c2 138 b.call(printf, "hello from b!\n");
Bogdan Marinescu 0:a792d4bf36c2 139
Bogdan Marinescu 0:a792d4bf36c2 140 EventQueue c;
Bogdan Marinescu 0:a792d4bf36c2 141 c.call(printf, "hello from c!\n");
Bogdan Marinescu 0:a792d4bf36c2 142
Bogdan Marinescu 0:a792d4bf36c2 143 // Chain c and b onto a's event queue. Both c and b will be dispatched
Bogdan Marinescu 0:a792d4bf36c2 144 // in the context of a's dispatch function.
Bogdan Marinescu 0:a792d4bf36c2 145 c.chain(&a);
Bogdan Marinescu 0:a792d4bf36c2 146 b.chain(&a);
Bogdan Marinescu 0:a792d4bf36c2 147
Bogdan Marinescu 0:a792d4bf36c2 148 // Dispatching a will in turn dispatch b and c, printing hello from
Bogdan Marinescu 0:a792d4bf36c2 149 // all three queues
Bogdan Marinescu 0:a792d4bf36c2 150 a.dispatch();
Bogdan Marinescu 0:a792d4bf36c2 151 ```
Bogdan Marinescu 0:a792d4bf36c2 152
Bogdan Marinescu 0:a792d4bf36c2 153