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docs(api-condvar): Update documentation for the ConditionVariable API 

- Hide protected member structures from doxygen.
- Add some more details/comments to the example.
- Add some defined/undefined behaviours.
- Add some additional details to function documentation
pull/8511/head
Steve Cartmell 2018-10-23 15:17:44 +01:00
parent ba23fef90b
commit c86ceb1bc1
1 changed files with 124 additions and 52 deletions
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176
rtos/ConditionVariable.h
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@ -35,26 +35,44 @@ namespace rtos {
struct Waiter;
/** This class provides a safe way to wait for or send notifications of condition changes
/** The ConditionVariable class is a synchronization primitive that allows
* threads to wait until a particular condition occurs.
*
* 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
* The condition variable 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.
* 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 will be 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.
*
* # Undefined behavior
* 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.
*
* ## Defined behavior
* - All threads that are waiting on the condition variable will wake when
* ConditionVariable::notify_all is called.
* - At least one thread that is waiting on the condition variable will wake
* when ConditionVariable::notify_one is called.
* - While waiting for a thread is waiting for notification of a
* ConditionVariable it will release the lock held on the mutex.
* - The ConditionVariable will reacquire the mutex lock before exiting the wait
* function.
*
* ## 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
* - 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.
* - 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
* 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
@ -65,60 +83,74 @@ struct Waiter;
* @note Synchronization level: Thread safe
*
* Example:
*
* @code
* #include "mbed.h"
*
* Mutex mutex;
* ConditionVariable cond(mutex);
* ConditionVariable cv(mutex);
*
* // These variables are protected by locking mutex
* uint32_t count = 0;
* uint32_t work_count = 0;
* bool done = false;
*
* void worker_thread()
* {
* mutex.lock();
* do {
* printf("Worker: Count %lu\r\n", count);
* // Acquire lock on mutex before accessing protected variables and waiting.
* mutex.lock();
*
* // Wait for a condition to change
* cond.wait();
* while (done == false) {
* printf("Worker thread: Count: %lu\r\n", work_count);
*
* } while (!done);
* printf("Worker: Exiting\r\n");
* mutex.unlock();
* // 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++) {
*
* 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);
* }
* 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 done and notify waiters of this
* done = true;
* printf("Main: Set done\r\n");
* cond.notify_all();
*
* // Change count and notify waiters of this
* 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();
*
* thread.join();
* 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
/** Create and initialize a ConditionVariable object
*
* @note You cannot call this function from ISR context.
*/
@ -126,17 +158,23 @@ public:
/** Wait for a notification
*
* Wait until a notification occurs.
* 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
* 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
* been met.
*
* @note - The current thread will release the lock while inside the wait
* function and reacquire it upon exiting the function.
*
* Example:
* @code
* mutex.lock();
*
* while (!condition_met) {
* cond.wait();
* }
@ -151,15 +189,23 @@ public:
void wait();
/** Wait for a notification until 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
* 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
* been met.
*
* @note - The current thread will release the lock while inside the wait
* function and reacquire it upon exiting the function.
*
* Example:
* @code
@ -184,15 +230,23 @@ public:
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 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
* 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
* been met.
*
* @note - The current thread will release the lock while inside the wait
* function and reacquire it upon exiting the function.
*
* Example:
* @code
@ -218,7 +272,14 @@ public:
/** 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
* This function will unblock 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 which is unblocked on ConditionVariable::notify_one is
* undefined if there are multiple waiters.
*
* @note You cannot call this function from ISR context.
*/
@ -226,7 +287,15 @@ public:
/** 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
* This function will unblock 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.
*/
@ -238,6 +307,7 @@ public:
*/
~ConditionVariable();
#if !defined(DOXYGEN_ONLY)
protected:
struct Waiter {
Waiter();
@ -247,10 +317,12 @@ protected:
bool in_list;
};
private:
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)
};
}