include/ruby/thread_native.h: add doxygen

Must not be a bad idea to improve documents. [ci skip]

include/ruby/thread_native.h

@@ -9,9 +9,7 @@
  *             Permission  is hereby  granted,  to  either redistribute  and/or
  *             modify this file, provided that  the conditions mentioned in the
  *             file COPYING are met.  Consult the file for details.
- */
-
-/*
+ *
  * This file contains wrapper APIs for native thread primitives
  * which Ruby interpreter uses.
  *
@@ -21,7 +19,6 @@
  * please use Mutex directly.
  */
 
-
 #if defined(_WIN32)
 #include <windows.h>
 typedef HANDLE rb_nativethread_id_t;
@@ -40,33 +37,163 @@ typedef pthread_t rb_nativethread_id_t;
 typedef pthread_mutex_t rb_nativethread_lock_t;
 typedef pthread_cond_t rb_nativethread_cond_t;
 
+#elif defined(__DOXYGEN__)
+
+/** Opaque type that holds an ID of a native thread. */
+struct rb_nativethread_id_t;
+
+/** Opaque type that holds a lock. */
+struct rb_nativethread_lock_t;
+
+/** Opaque type that holds a condition variable. */
+struct rb_nativethread_cond_t;
+
 #else
 #error "unsupported thread type"
 
 #endif
 
-RUBY_SYMBOL_EXPORT_BEGIN
+RBIMPL_SYMBOL_EXPORT_BEGIN()
 
+/**
+ * Queries the ID of the native thread that is calling this function.
+ *
+ * @return The caller thread's native ID.
+ */
 rb_nativethread_id_t rb_nativethread_self(void);
 
+/**
+ * Fills the passed lock with an initial value.
+ *
+ * @param[out]  lock  A mutex to initialise.
+ * @post        `lock` is updated to its initial state.
+ *
+ * @internal
+ *
+ * There is no data structure that  analogous to pthread_once_t in ruby.  It is
+ * pretty  much tricky  (if  not  impossible) to  properly  initialise a  mutex
+ * exactly once.
+ */
 void rb_nativethread_lock_initialize(rb_nativethread_lock_t *lock);
+
+/**
+ * Destroys the passed mutex.
+ *
+ * @param[out]  lock  A mutex to kill.
+ * @post        `lock` is no longer eligible for other functions.
+ *
+ * @internal
+ *
+ * It  is  an  undefined  behaviour  (see  `pthread_mutex_destroy(3posix)`)  to
+ * destroy a locked  mutex.  So it has  to be unlocked.  But  an unlocked mutex
+ * can of course  be locked by another thread.  That's  the ultimate reason why
+ * we do mutex.   There is an inevitable race condition  here.  2017 edition of
+ * IEEE 1003.1 issue 7 says in its  rationale that "care must be taken".  Care?
+ * How?
+ *
+ * @shyouhei thinks that POSIX is broken by design.
+ */
 void rb_nativethread_lock_destroy(rb_nativethread_lock_t *lock);
+
+/**
+ * Blocks until the current thread obtains a lock.
+ *
+ * @param[out]  lock  A mutex to lock.
+ * @post        `lock` is owned by the current native thread.
+ */
 void rb_nativethread_lock_lock(rb_nativethread_lock_t *lock);
+
+/**
+ * Releases a lock.
+ *
+ * @param[out]  lock  A mutex to unlock.
+ * @pre         `lock` is owned by the current native thread.
+ * @post        `lock` is not owned by the current native thread.
+ */
 void rb_nativethread_lock_unlock(rb_nativethread_lock_t *lock);
 
+/** @alias{rb_nativethread_lock_lock} */
 void rb_native_mutex_lock(rb_nativethread_lock_t *lock);
+
+/**
+ * Identical  to  rb_native_mutex_lock(),  except  it  doesn't  block  in  case
+ * rb_native_mutex_lock() would.
+ *
+ * @param[out]  lock   A mutex to lock.
+ * @retval      0      `lock` is successfully owned by the current thread.
+ * @retval      EBUSY  `lock` is owned by someone else.
+ */
 int  rb_native_mutex_trylock(rb_nativethread_lock_t *lock);
+
+/** @alias{rb_nativethread_lock_unlock} */
 void rb_native_mutex_unlock(rb_nativethread_lock_t *lock);
+
+/** @alias{rb_nativethread_lock_initialize} */
 void rb_native_mutex_initialize(rb_nativethread_lock_t *lock);
+
+/** @alias{rb_nativethread_lock_destroy} */
 void rb_native_mutex_destroy(rb_nativethread_lock_t *lock);
 
+/**
+ * Signals a condition variable.
+ *
+ * @param[out]  cond  A condition variable to ping.
+ * @post        More than one threads waiting for `cond` gets signalled.
+ * @note        This  function   can  spuriously  wake  multiple   threads  up.
+ *              `pthread_cond_signal(3posix)` says  it can even  be "impossible
+ *              to avoid  the unblocking of more  than one thread blocked  on a
+ *              condition variable".  Just brace spurious wakeups.
+ */
 void rb_native_cond_signal(rb_nativethread_cond_t *cond);
+
+/**
+ * Signals a condition variable.
+ *
+ * @param[out]  cond  A condition variable to ping.
+ * @post        All threads waiting for `cond` gets signalled.
+ */
 void rb_native_cond_broadcast(rb_nativethread_cond_t *cond);
+
+/**
+ * Waits for the passed condition variable to be signalled.
+ *
+ * @param[out]  cond   A condition variable to wait.
+ * @param[out]  mutex  A mutex.
+ * @pre         `mutex` is owned by the current thread.
+ * @post        `mutex` is owned by the current thread.
+ * @note        This can wake up spuriously.
+ */
 void rb_native_cond_wait(rb_nativethread_cond_t *cond, rb_nativethread_lock_t *mutex);
+
+/**
+ * Identical to rb_native_cond_wait(), except  it additionally takes timeout in
+ * msec resolution.  Timeouts can be detected by catching exceptions.
+ *
+ * @param[out]  cond                 A condition variable to wait.
+ * @param[out]  mutex                A mutex.
+ * @param[in]   msec                 Timeout.
+ * @exception   rb_eSystemCallError  `Errno::ETIMEDOUT` for timeout.
+ * @pre         `mutex` is owned by the current thread.
+ * @post        `mutex` is owned by the current thread.
+ * @note        This can wake up spuriously.
+ */
 void rb_native_cond_timedwait(rb_nativethread_cond_t *cond, rb_nativethread_lock_t *mutex, unsigned long msec);
+
+/**
+ * Fills the passed condition variable with an initial value.
+ *
+ * @param[out]  cond  A condition variable to initialise.
+ * @post        `cond` is updated to its initial state.
+ */
 void rb_native_cond_initialize(rb_nativethread_cond_t *cond);
+
+/**
+ * Destroys the passed condition variable.
+ *
+ * @param[out]  cond  A condition variable to kill.
+ * @post        `cond` is no longer eligible for other functions.
+ */
 void rb_native_cond_destroy(rb_nativethread_cond_t *cond);
 
-RUBY_SYMBOL_EXPORT_END
-
+RBIMPL_SYMBOL_EXPORT_END()
 #endif