Diff: mbed-os/events/README.md

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+## The mbed-events library ##
+
+The mbed-events library provides a flexible queue for scheduling events.
+
+``` cpp
+#include "mbed_events.h"
+#include <stdio.h>
+
+int main() {
+    // creates a queue with the default size
+    EventQueue queue;
+
+    // events are simple callbacks
+    queue.call(printf, "called immediately\n");
+    queue.call_in(2000, printf, "called in 2 seconds\n");
+    queue.call_every(1000, printf, "called every 1 seconds\n");
+
+    // events are executed by the dispatch method
+    queue.dispatch();
+}
+```
+
+The mbed-events library can be used as a normal event loop, or it can be
+backgrounded on a single hardware timer or even another event loop. It is
+both thread and irq safe, and provides functions for easily composing 
+independent event queues.
+
+The mbed-events library can act as a drop-in scheduler, provide synchronization
+between multiple threads, or just act as a mechanism for moving events out of 
+interrupt contexts.
+
+### Usage ###
+
+The core of the mbed-events library is the [EventQueue](EventQueue.h) class,
+which represents a single event queue. The `EventQueue::dispatch` function
+runs the queue, providing the context for executing events.
+
+``` cpp
+// Creates an event queue enough buffer space for 32 Callbacks. This
+// is the default if no argument was provided. Alternatively the size
+// can just be specified in bytes.
+EventQueue queue(32*EVENTS_EVENT_SIZE);
+
+// Events can be posted to the underlying event queue with dynamic
+// context allocated from the specified buffer
+queue.call(printf, "hello %d %d %d %d\n", 1, 2, 3, 4);
+queue.call(&serial, &Serial::printf, "hi\n");
+
+// The dispatch function provides the context for the running the queue
+// and can take a millisecond timeout to run for a fixed time or to just
+// dispatch any pending events
+queue.dispatch();
+```
+
+The EventQueue class provides several call functions for posting events
+to the underlying event queue. The call functions are thread and irq safe,
+don't need the underlying loop to be running, and provide an easy mechanism
+for moving events out of interrupt contexts.
+
+``` cpp
+// Simple call function registers events to be called as soon as possible
+queue.call(doit);
+queue.call(printf, "called immediately\n");
+
+// The call_in function registers events to be called after a delay
+// specified in milliseconds
+queue.call_in(2000, doit_in_two_seconds);
+queue.call_in(300, printf, "called in 0.3 seconds\n");
+
+// The call_every function registers events to be called repeatedly
+// with a period specified in milliseconds
+queue.call_every(2000, doit_every_two_seconds);
+queue.call_every(400, printf, "called every 0.4 seconds\n");
+```
+
+The call functions return an id that uniquely represents the event in the 
+the event queue. This id can be passed to `EventQueue::cancel` to cancel
+an in-flight event.
+
+``` cpp
+// The event id uniquely represents the event in the queue
+int id = queue.call_in(100, printf, "will this work?\n");
+
+// If there was not enough memory necessary to allocate the event,
+// an id of 0 is returned from the call functions
+if (id) {
+    error("oh no!");
+}
+
+// Events can be cancelled as long as they have not been dispatched. If the
+// event has already expired, cancel has no side-effects.
+queue.cancel(id);
+```
+
+For a more fine-grain control of event dispatch, the `Event` class can be
+manually instantiated and configured. An `Event` represents an event as
+a C++ style function object and can be directly passed to other APIs that
+expect a callback.
+
+``` cpp
+// Creates an event bound to the specified event queue
+EventQueue queue;
+Event<void()> event(&queue, doit);
+
+// The event can be manually configured for special timing requirements
+// specified in milliseconds
+event.delay(10);
+event.period(10000);
+
+// Posted events are dispatched in the context of the queue's
+// dispatch function
+queue.dispatch();
+
+// Events can also pass arguments to the underlying callback when both
+// initially constructed and posted.
+Event<void(int, int)> event(&queue, printf, "received %d and %d\n");
+
+// Events can be posted multiple times and enqueue gracefully until
+// the dispatch function is called.
+event.post(1, 2);
+event.post(3, 4);
+event.post(5, 6);
+
+queue.dispatch();
+```
+
+Event queues easily align with module boundaries, where internal state can
+be implicitly synchronized through event dispatch. Multiple modules can
+use independent event queues, but still be composed through the
+`EventQueue::chain` function.
+
+``` cpp
+// Create some event queues with pending events
+EventQueue a;
+a.call(printf, "hello from a!\n");
+
+EventQueue b;
+b.call(printf, "hello from b!\n");
+
+EventQueue c;
+c.call(printf, "hello from c!\n");
+
+// Chain c and b onto a's event queue. Both c and b will be dispatched
+// in the context of a's dispatch function.
+c.chain(&a);
+b.chain(&a);
+
+// Dispatching a will in turn dispatch b and c, printing hello from
+// all three queues
+a.dispatch();
+```
+
+