Add the PolledQueue implementation of TaskQueue

Add the PolledQueue class which provides a TaskQueue which is run
by calling PolledQueue::process.

usb/device/utilities/events/PolledQueue.cpp

@@ -0,0 +1,91 @@
+/* events
+ * Copyright (c) 2018 ARM Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#include "events/PolledQueue.h"
+
+#include "events/mbed_events.h"
+#include "platform/Callback.h"
+
+
+PolledQueue::PolledQueue(mbed::Callback<void()> cb): _cb(cb)
+{
+
+}
+
+PolledQueue::~PolledQueue()
+{
+
+}
+
+void PolledQueue::dispatch()
+{
+    core_util_critical_section_enter();
+    uint64_t buf[MBED_MAX_TASK_SIZE / sizeof(uint64_t)];
+
+    while (true) {
+
+        // Atomically dequeue the task and copy the callback
+        TaskBase *task = _list.dequeue();
+        if (!task) {
+            break;
+        }
+        MBED_ASSERT(sizeof(buf) >= task_size(task));
+        TaskBase::run_callback_t callback = task_start(task, (uint8_t*)buf, sizeof(buf));
+
+        // Run the callback outside the critical section
+        core_util_critical_section_exit();
+        callback((uint8_t*)buf);
+        core_util_critical_section_enter();
+
+        // Finish
+        task_finish(task);
+        task = NULL;
+
+    }
+
+    core_util_critical_section_exit();
+}
+
+void PolledQueue::attach(mbed::Callback<void()> cb)
+{
+    core_util_critical_section_enter();
+
+    _cb = cb;
+
+    core_util_critical_section_exit();
+}
+
+void PolledQueue::post(TaskBase *task)
+{
+    core_util_critical_section_enter();
+
+    bool empty = _list.head() == NULL;
+    _list.remove(task);
+    _list.enqueue(task);
+    if (empty && _cb) {
+        _cb();
+    }
+
+    core_util_critical_section_exit();
+}
+
+void PolledQueue::cancel(TaskBase *task)
+{
+    core_util_critical_section_enter();
+
+    _list.remove(task);
+
+    core_util_critical_section_exit();
+}

usb/device/utilities/events/PolledQueue.h

@@ -0,0 +1,71 @@
+/* events
+ * Copyright (c) 2018 ARM Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef POLLED_QUEUE_H
+#define POLLED_QUEUE_H
+
+#include "events/TaskQueue.h"
+#include "platform/Callback.h"
+#include "LinkedList.h"
+namespace events {
+/** \addtogroup events */
+
+
+/** PolledQueue
+ *
+ * This class is an implementation of TaskQueue which is
+ * processed synchronously by calls to dispatch.
+ * @ingroup events
+ */
+class PolledQueue: public TaskQueue {
+public:
+
+    /** Create a PolledQueue
+     *
+     *  Create an event queue.
+     *
+     *  @param cb Callback called when dispatch needs to be called
+     */
+    PolledQueue(mbed::Callback<void()> cb=NULL);
+
+    virtual ~PolledQueue();
+
+    virtual void post(TaskBase *event);
+
+    virtual void cancel(TaskBase *event);
+
+    /**
+     * Process all the events in this queue
+     */
+    void dispatch();
+
+    /**
+     * Attach a callback indicating that this queue needs to be processed
+     *
+     * @param cb Callback called when dispatch needs to be called
+     */
+    void attach(mbed::Callback<void()> cb);
+
+protected:
+
+    mbed::Callback<void()> _cb;
+    LinkedList<TaskBase> _list;
+
+};
+
+}
+#endif
+