/* 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 "rtos/Semaphore.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
*
* @note You cannot call this function from ISR context.
*/
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
*
* @note You cannot call this function from ISR context.
*/
void wait();
/** Wait for a notification until specified time
*
* @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 they are waiting on has
* been met
*
* 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
*
* @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();
*
* 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.
*
* @note - The thread calling this function must be the owner of the ConditionVariable's mutex
*
* @note You cannot call this function from ISR context.
*/
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
*
* @note You cannot call this function from ISR context.
*/
void notify_all();
/** ConditionVariable destructor
*
* @note You cannot call this function from ISR context.
*/
~ConditionVariable();
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
/** @}*/
