/* 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 "rtos/mbed_rtos_types.h"
#include "rtos/Mutex.h"
#include "rtos/Semaphore.h"
#include "platform/NonCopyable.h"
#if MBED_CONF_RTOS_PRESENT || defined(DOXYGEN_ONLY)
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
#endif
/** @}*/
