Condition variables

[carlescufi]

Zephyr kernel APIs that cover:

pthread_cond_wait
pthread_cond_timedwait
pthread_cond_signal
pthread_cond_broadcast

[nashif]

Draft API for condition variables...

/**
 * @brief Initialize a condition variable
 *
 * @param condvar pointer to a @p k_condvar structure
 * @retval 0 Condition variable created successfully
 */
__syscall int k_condvar_init(struct k_condvar *condvar);

/**
 * @brief Signals one thread that is pending on the condition variable
 *
 *
 * @param condvar pointer to a @p k_condvar structure
 * @retval 0 On success
 */
__syscall int k_condvar_signal(struct k_condvar *condvar);

/**
 * @brief Broadcast to all threads that are pending on the condition variable
 *
 * @param condvar pointer to a @p k_condvar structure
 * @retval 0 On success
 */
__syscall int k_condvar_broadcast(struct k_condvar *condvar);

/**
 * @brief Waits on the condition variable releasing the mutex lock
 *
 * Automically releases the currently owned mutex, blocks the current thread
 * waiting on the condition variable specified by @a condvar,
 * and finally acquires the mutex again.
 *
 * The waiting thread unblocks only after another thread calls k_condvar_signal, or
 * k_condvar_broadcast with the same condition variable.
 *
 * @param condvar pointer to a @p k_condvar structure
 * @param mutex Address of the mutex.
 * @param timeout Waiting period for the condition variable in ms
 *                or one of the special values K_NO_WAIT and K_FOREVER.
 * @return
 */
__syscall int k_condvar_wait(struct k_condvar *condvar, struct k_mutex *mutex,
			     k_timeout_t timeout);

/**
 * @brief Statically define and initialize a condition variable.
 *
 * The condition variable can be accessed outside the module where it is defined using:
 *
 * @code extern struct k_condvar <name>; @endcode
 *
 * @param name Name of the condition variable.
 */
#define K_CONDVAR_DEFINE(name)                                                 \
	Z_STRUCT_SECTION_ITERABLE(k_condvar, name) =                           \
		Z_CONDVAR_INITIALIZER(name);