Add ConditionVariable to mbed rtos

Add the ConditionVariable class to mbed rtos to provide easier and
safer synchronization.

rtos/ConditionVariable.cpp

@@ -0,0 +1,136 @@
+/* mbed Microcontroller Library
+ * Copyright (c) 2017-2017 ARM Limited
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+#include "rtos/ConditionVariable.h"
+#include "rtos/Semaphore.h"
+#include "rtos/Thread.h"
+
+#include "mbed_error.h"
+#include "mbed_assert.h"
+
+namespace rtos {
+
+#define RESUME_SIGNAL      (1 << 15)
+
+struct Waiter {
+    Waiter();
+    Semaphore sem;
+    Waiter *prev;
+    Waiter *next;
+    bool in_list;
+};
+
+Waiter::Waiter(): sem(0), prev(NULL), next(NULL), in_list(false)
+{
+    // No initialization to do
+}
+
+ConditionVariable::ConditionVariable(Mutex &mutex): _mutex(mutex), _wait_list(NULL)
+{
+    // No initialization to do
+}
+
+void ConditionVariable::wait()
+{
+    wait_for(osWaitForever);
+}
+
+bool ConditionVariable::wait_for(uint32_t millisec)
+{
+    Waiter current_thread;
+    MBED_ASSERT(_mutex.get_owner() == Thread::gettid());
+    MBED_ASSERT(_mutex._count == 1);
+    _add_wait_list(&current_thread);
+
+    _mutex.unlock();
+
+    int32_t sem_count = current_thread.sem.wait(millisec);
+    bool timeout = (sem_count > 0) ? false : true;
+
+    _mutex.lock();
+
+    if (current_thread.in_list) {
+        _remove_wait_list(&current_thread);
+    }
+
+    return timeout;
+}
+
+void ConditionVariable::notify_one()
+{
+    MBED_ASSERT(_mutex.get_owner() == Thread::gettid());
+    if (_wait_list != NULL) {
+        _wait_list->sem.release();
+        _remove_wait_list(_wait_list);
+    }
+}
+
+void ConditionVariable::notify_all()
+{
+    MBED_ASSERT(_mutex.get_owner() == Thread::gettid());
+    while (_wait_list != NULL) {
+        _wait_list->sem.release();
+        _remove_wait_list(_wait_list);
+    }
+}
+
+void ConditionVariable::_add_wait_list(Waiter * waiter)
+{
+    if (NULL == _wait_list) {
+        // Nothing in the list so add it directly.
+        // Update prev pointer to reference self
+        _wait_list = waiter;
+        waiter->prev = waiter;
+    } else {
+        // Add after the last element
+        Waiter *last = _wait_list->prev;
+        last->next = waiter;
+        waiter->prev = last;
+        _wait_list->prev = waiter;
+    }
+    waiter->in_list = true;
+}
+
+void ConditionVariable::_remove_wait_list(Waiter * waiter)
+{
+    // Remove this element from the start of the list
+    Waiter * next = waiter->next;
+    if (waiter == _wait_list) {
+        _wait_list = next;
+    }
+    if (next != NULL) {
+        next = waiter->prev;
+    }
+    Waiter * prev = waiter->prev;
+    if (prev != NULL) {
+        prev = waiter->next;
+    }
+    waiter->next = NULL;
+    waiter->prev = NULL;
+    waiter->in_list = false;
+}
+
+ConditionVariable::~ConditionVariable()
+{
+    MBED_ASSERT(NULL == _wait_list);
+}
+
+}

rtos/ConditionVariable.h

@@ -0,0 +1,205 @@
+/* mbed Microcontroller Library
+ * Copyright (c) 2017-2017 ARM Limited
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+#ifndef CONDITIONVARIABLE_H
+#define CONDITIONVARIABLE_H
+
+#include <stdint.h>
+#include "cmsis_os.h"
+#include "rtos/Mutex.h"
+
+#include "platform/NonCopyable.h"
+
+namespace rtos {
+/** \addtogroup rtos */
+/** @{*/
+
+struct Waiter;
+
+/** This class provides a safe way to wait for or send notifications of condition changes
+ *
+ * This class is used in conjunction with a mutex to safely wait for or
+ * notify waiters of condition changes to a resource accessible by multiple
+ * threads.
+ *
+ * # Defined behavior
+ * - All threads waiting on the condition variable wake when
+ *   ConditionVariable::notify_all is called.
+ * - If one or more threads are waiting on the condition variable at least
+ *   one of them wakes when ConditionVariable::notify is called.
+ *
+ * # Undefined behavior
+ * - The thread which is unblocked on ConditionVariable::notify_one is
+ *   undefined if there are multiple waiters.
+ * - The order which in which waiting threads acquire the condition variable's
+ *   mutex after ConditionVariable::notify_all is called is undefined.
+ * - When ConditionVariable::notify_one or ConditionVariable::notify_all is
+ *   called and there are one or more waiters and one or more threads attempting
+ *   to acquire the condition variable's mutex the order in which the mutex is
+ *   acquired is undefined.
+ * - The behavior of ConditionVariable::wait and ConditionVariable::wait_for
+ *   is undefined if the condition variable's mutex is locked more than once by
+ *   the calling thread.
+ * - Spurious notifications (not triggered by the application) can occur
+ *   and it is not defined when these occur.
+ *
+ * @note Synchronization level: Thread safe
+ *
+ * Example:
+ * @code
+ * #include "mbed.h"
+ *
+ * Mutex mutex;
+ * ConditionVariable cond(mutex);
+ *
+ * // These variables are protected by locking mutex
+ * uint32_t count = 0;
+ * bool done = false;
+ *
+ * void worker_thread()
+ * {
+ *     mutex.lock();
+ *     do {
+ *         printf("Worker: Count %lu\r\n", count);
+ *
+ *         // Wait for a condition to change
+ *         cond.wait();
+ *
+ *     } while (!done);
+ *     printf("Worker: Exiting\r\n");
+ *     mutex.unlock();
+ * }
+ *
+ * int main() {
+ *     Thread thread;
+ *     thread.start(worker_thread);
+ *
+ *     for (int i = 0; i < 5; i++) {
+ *
+ *         mutex.lock();
+ *         // Change count and notify waiters of this
+ *         count++;
+ *         printf("Main: Set count to %lu\r\n", count);
+ *         cond.notify_all();
+ *         mutex.unlock();
+ *
+ *         wait(1.0);
+ *     }
+ *
+ *     mutex.lock();
+ *     // Change done and notify waiters of this
+ *     done = true;
+ *     printf("Main: Set done\r\n");
+ *     cond.notify_all();
+ *     mutex.unlock();
+ *
+ *     thread.join();
+ * }
+ * @endcode
+ */
+class ConditionVariable : private mbed::NonCopyable<ConditionVariable> {
+public:
+    /** Create and Initialize a ConditionVariable object */
+    ConditionVariable(Mutex &mutex);
+
+    /** Wait for a notification
+     *
+     * Wait until a notification occurs.
+     *
+     * @note - The thread calling this function must be the owner of the
+     * ConditionVariable's mutex and it must be locked exactly once
+     * @note - Spurious notifications can occur so the caller of this API
+     * should check to make sure the condition they are waiting on has
+     * been met
+     *
+     * Example:
+     * @code
+     * mutex.lock();
+     * while (!condition_met) {
+     *     cond.wait();
+     * }
+     *
+     * function_to_handle_condition();
+     *
+     * mutex.unlock();
+     * @endcode
+     */
+    void wait();
+
+    /** Wait for a notification or timeout
+     *
+     * @param   millisec  timeout value or osWaitForever in case of no time-out.
+     * @return  true if a timeout occurred, false otherwise.
+     *
+     * @note - The thread calling this function must be the owner of the
+     * ConditionVariable's mutex and it must be locked exactly once
+     * @note - Spurious notifications can occur so the caller of this API
+     * should check to make sure the condition they are waiting on has
+     * been met
+     *
+     * Example:
+     * @code
+     * mutex.lock();
+     * Timer timer;
+     * timer.start();
+     *
+     * bool timed_out = false;
+     * uint32_t time_left = TIMEOUT;
+     * while (!condition_met && !timed_out) {
+     *     timed_out = cond.wait_for(time_left);
+     *     uint32_t elapsed = timer.read_ms();
+     *     time_left = elapsed > TIMEOUT ? 0 : TIMEOUT - elapsed;
+     * }
+     *
+     * if (condition_met) {
+     *     function_to_handle_condition();
+     * }
+     *
+     * mutex.unlock();
+     * @endcode
+     */
+    bool wait_for(uint32_t millisec);
+
+    /** Notify one waiter on this condition variable that a condition changed.
+     *
+     * @note - The thread calling this function must be the owner of the ConditionVariable's mutex
+     */
+    void notify_one();
+
+    /** Notify all waiters on this condition variable that a condition changed.
+     *
+     * @note - The thread calling this function must be the owner of the ConditionVariable's mutex
+     */
+    void notify_all();
+
+    ~ConditionVariable();
+
+private:
+    void _add_wait_list(Waiter * waiter);
+    void _remove_wait_list(Waiter * waiter);
+    Mutex &_mutex;
+    Waiter *_wait_list;
+};
+
+}
+#endif
+
+/** @}*/

rtos/Mutex.cpp

@@ -27,7 +27,7 @@
 
 namespace rtos {
 
-Mutex::Mutex()
+Mutex::Mutex(): _count(0)
 {
     constructor();
 }
@@ -50,17 +50,31 @@ void Mutex::constructor(const char *name)
 }
 
 osStatus Mutex::lock(uint32_t millisec) {
-    return osMutexAcquire(_id, millisec);
+    osStatus status = osMutexAcquire(_id, millisec);
+    if (osOK == status) {
+        _count++;
+    }
+    return status;
 }
 
 bool Mutex::trylock() {
-    return (osMutexAcquire(_id, 0) == osOK);
+    if (osMutexAcquire(_id, 0) == osOK) {
+        _count++;
+        return true;
+    } else {
+        return false;
+    }
 }
 
 osStatus Mutex::unlock() {
+    _count--;
     return osMutexRelease(_id);
 }
 
+osThreadId Mutex::get_owner() {
+    return osMutexGetOwner(_id);
+}
+
 Mutex::~Mutex() {
     osMutexDelete(_id);
 }

rtos/Mutex.h

@@ -76,14 +76,21 @@ public:
      */
     osStatus unlock();
 
+    /** Get the owner the this mutex
+      @return  the current owner of this mutex.
+     */
+    osThreadId get_owner();
+
     ~Mutex();
 
 private:
     void constructor(const char *name = NULL);
+    friend class ConditionVariable;
 
     osMutexId_t               _id;
     osMutexAttr_t             _attr;
     mbed_rtos_storage_mutex_t _obj_mem;
+    uint32_t                  _count;
 };
 
 }

rtos/rtos.h

@@ -34,6 +34,7 @@
 #include "rtos/MemoryPool.h"
 #include "rtos/Queue.h"
 #include "rtos/EventFlags.h"
+#include "rtos/ConditionVariable.h"
 
 using namespace rtos;