Diff: rtos/ConditionVariable.h

Revision:

0:38ceb79fef03

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rtos/ConditionVariable.h	Wed Nov 28 15:10:15 2018 +0000
@@ -0,0 +1,331 @@
+/* Mbed Microcontroller Library
+ * Copyright (c) 2017-2018 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 "rtos/Semaphore.h"
+
+#include "platform/NonCopyable.h"
+
+namespace rtos {
+/** \addtogroup rtos */
+/** @{*/
+
+struct Waiter;
+
+/** The ConditionVariable class is a synchronization primitive that allows
+ *   threads to wait until a particular condition occurs.
+ *
+ * Use the condition variable in conjunction with a mutex to safely wait for
+ * or notify waiters of condition changes to a resource accessible by multiple
+ * threads.
+ *
+ * The thread that intends to wait on a ConditionVariable must:
+ * - Acquire a lock on a mutex.
+ * - Execute `wait`, `wait_for` or `wait_until`. While the thread is waiting,
+ *   the mutex is unlocked.
+ * - When the condition variable has been notified, or in the case of `wait_for`
+ *   and `wait_until` the timeout expires, the thread is awakened.
+ *
+ * The thread that intends to notify a ConditionVariable must:
+ * - Acquire a lock on the mutex used to construct the condition variable.
+ * - Execute `notify_one` or `notify_all` on the condition variable.
+ *
+ * All threads waiting on the condition variable wake when
+ *   `ConditionVariable::notify_all` is called.
+ * At least one thread waiting on the condition variable wakes
+ *   when `ConditionVariable::notify_one` is called.
+ * 
+ * While a thread is waiting for notification of a
+ *   ConditionVariable, it releases the lock held on the mutex. 
+ * The ConditionVariable reacquires the mutex lock before exiting the wait
+ *   function.
+ *
+ * #### Unspecified behavior
+ * - The thread that is unblocked on `ConditionVariable::notify_one` is
+ *   unspecified if there are multiple waiters.
+ * - 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 unspecified.
+ * - Spurious notifications (not triggered by the application) can occur.
+ *
+ * #### Undefined behavior
+ * - Calling wait if the mutex is not locked by the current thread is undefined
+ *   behavior.
+ * - The order in which waiting threads acquire the condition variable's
+ *   mutex after `ConditionVariable::notify_all` is called 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.
+ *
+ * @note Synchronization level: Thread safe
+ *
+ * Example:
+ *
+ * @code
+ * #include "mbed.h"
+ *
+ * Mutex mutex;
+ * ConditionVariable cv(mutex);
+ *
+ * // These variables are protected by locking the mutex.
+ * uint32_t work_count = 0;
+ * bool done = false;
+ *
+ * void worker_thread()
+ * {
+ *   // Acquire lock on mutex before accessing protected variables and waiting.
+ *   mutex.lock();
+ *
+ *   while (done == false) {
+ *     printf("Worker thread: Count: %lu\r\n", work_count);
+ *
+ *     // Wait for main thread to notify the condition variable.
+ *     printf("Worker thread: Waiting\r\n");
+ *     cv.wait();
+ *   }
+ *
+ *   printf("Worker: Exiting\r\n");
+ *
+ *   // The condition variable acquires the lock when exiting the `wait` function.
+ *   // Unlock mutex when exiting the thread.
+ *   mutex.unlock();
+ * }
+ *
+ * int main()
+ * {
+ *   Thread thread;
+ *   thread.start(worker_thread);
+ *
+ *   for (int i = 0; i < 5; i++) {
+ *     // Acquire lock on mutex before modifying variables and notifying.
+ *     mutex.lock();
+ *
+ *     // Change count and notify waiters.
+ *     work_count++;
+ *     printf("Main thread: Set count to: %lu\r\n", work_count);
+ *     printf("Main thread: Notifying worker thread\r\n");
+ *     cv.notify_all();
+ *
+ *     // Mutex must be unlocked before the worker thread can acquire it.
+ *     mutex.unlock();
+ *
+ *     wait(1.0);
+ *   }
+ *
+ *   // Change done and notify waiters of this.
+ *   mutex.lock();
+ *   done = true;
+ *   cv.notify_all();
+ *   mutex.unlock();
+ *
+ *   thread.join();
+ *
+ *   printf("Main: Exiting\r\n");
+ * }
+ * @endcode
+ */
+
+class ConditionVariable : private mbed::NonCopyable<ConditionVariable> {
+public:
+    /** Create and initialize a ConditionVariable object.
+     *
+     * @note You cannot call this function from ISR context.
+    */
+    ConditionVariable(Mutex &mutex);
+
+    /** Wait for a notification.
+     *
+     * Wait causes the current thread to block until the condition variable
+     * receives a notification from another thread.
+     *
+     * @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 the caller is waiting on has
+     * been met.
+     *
+     * @note - The current thread releases the lock while inside the wait
+     * function and reacquires it upon exiting the function.
+     *
+     * Example:
+     * @code
+     * mutex.lock();
+     *
+     * while (!condition_met) {
+     *     cond.wait();
+     * }
+     *
+     * function_to_handle_condition();
+     *
+     * mutex.unlock();
+     * @endcode
+     *
+     * @note You cannot call this function from ISR context.
+     */
+    void wait();
+
+    /** Wait for a notification until the specified time.
+     *
+     * Wait until causes the current thread to block until the condition
+     * variable is notified, or a specific time given by millisec parameter is
+     * reached.
+     *
+     * @param   millisec  Absolute end time referenced to `Kernel::get_ms_count()`
+     * @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 the caller is waiting on has
+     * been met.
+     *
+     * @note - The current thread releases the lock while inside the wait
+     * function and reacquires it upon exiting the function.
+     *
+     * Example:
+     * @code
+     * mutex.lock();
+     * uint64_t end_time = Kernel::get_ms_count() + COND_WAIT_TIMEOUT;
+     *
+     * while (!condition_met) {
+     *     if (cond.wait_until(end_time)) {
+     *         break;
+     *     }
+     * }
+     *
+     * if (condition_met) {
+     *     function_to_handle_condition();
+     * }
+     *
+     * mutex.unlock();
+     * @endcode
+     *
+     * @note You cannot call this function from ISR context.
+     */
+    bool wait_until(uint64_t millisec);
+
+    /** Wait for a notification or timeout.
+     *
+     * `Wait for` causes the current thread to block until the condition
+     * variable receives a notification from another thread, or the timeout
+     * specified by the millisec parameter is reached.
+     *
+     * @param   millisec  Timeout value or osWaitForever in case of no timeout.
+     * @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 the caller is waiting on has
+     * been met.
+     *
+     * @note - The current thread releases the lock while inside the wait
+     * function and reacquire it upon exiting the function.
+     *
+     * Example:
+     * @code
+     * mutex.lock();
+     *
+     * while (!condition_met) {
+     *     cond.wait_for(MAX_SLEEP_TIME);
+     *     if (!condition_met) {
+     *         do_other_work_while_condition_false();
+     *     }
+     * }
+     *
+     * if (condition_met) {
+     *     function_to_handle_condition();
+     * }
+     *
+     * mutex.unlock();
+     * @endcode
+     *
+     * @note You cannot call this function from ISR context.
+     */
+    bool wait_for(uint32_t millisec);
+
+    /** Notify one waiter on this condition variable that a condition changed.
+     *
+     * This function unblocks one of the threads waiting for the condition
+     * variable.
+     *
+     * @note - The thread calling this function must be the owner of the
+     * ConditionVariable's mutex.
+     *
+     * @note - The thread that is unblocked on ConditionVariable::notify_one is
+     * undefined if there are multiple waiters.
+     *
+     * @note You cannot call this function from ISR context.
+     */
+    void notify_one();
+
+    /** Notify all waiters on this condition variable that a condition changed.
+     *
+     * This function unblocks all of the threads waiting for the condition
+     * variable.
+     *
+     * @note - The thread calling this function must be the owner of the
+     * ConditionVariable's mutex.
+     *
+     * @note - If 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.
+     *
+     * @note You cannot call this function from ISR context.
+     */
+    void notify_all();
+
+    /** ConditionVariable destructor.
+     *
+     * @note You cannot call this function from ISR context.
+     */
+    ~ConditionVariable();
+
+#if !defined(DOXYGEN_ONLY)
+protected:
+    struct Waiter {
+        Waiter();
+        Semaphore sem;
+        Waiter *prev;
+        Waiter *next;
+        bool in_list;
+    };
+
+    static void _add_wait_list(Waiter **wait_list, Waiter *waiter);
+    static void _remove_wait_list(Waiter **wait_list, Waiter *waiter);
+    Mutex &_mutex;
+    Waiter *_wait_list;
+#endif // !defined(DOXYGEN_ONLY)
+};
+
+}
+#endif
+
+/** @}*/