libc: cleanup monitor implementation

- Explicit types for function and monitor execution results
- Remove pending flag and mutex (pending flag was moved to kernel)

repos/libports/src/lib/libc/internal/kernel.h

@@ -271,13 +271,16 @@ struct Libc::Kernel final : Vfs::Io_response_handler,
 
 		Pthread_pool _pthreads { _timer_accessor };
 
-		Monitor::Pool _monitors { };
+		Monitor::Pool _monitors { *this };
 
 		Reconstructible<Io_signal_handler<Kernel>> _execute_monitors {
 			_env.ep(), *this, &Kernel::_monitors_handler };
 
+		bool _execute_monitors_pending { false };
+
 		void _monitors_handler()
 		{
+			_execute_monitors_pending = false;
 			_monitors.execute_monitors();
 		}
 
@@ -532,26 +535,30 @@ struct Libc::Kernel final : Vfs::Io_response_handler,
 		/**
 		 * Monitor interface
 		 */
-		bool _monitor(Mutex &mutex, Function &fn, uint64_t timeout_ms) override
+		Monitor::Result _monitor(Mutex &mutex, Function &fn, uint64_t timeout_ms) override
 		{
 			if (_main_context()) {
 				Main_job job { fn, timeout_ms };
 
 				_monitors.monitor(mutex, job);
-				return job.completed();
+				return job.completed() ? Monitor::Result::COMPLETE
+				                       : Monitor::Result::TIMEOUT;
 
 			} else {
 				Pthread_job job { fn, _timer_accessor, timeout_ms };
 
 				_monitors.monitor(mutex, job);
-				return job.completed();
+				return job.completed() ? Monitor::Result::COMPLETE
+				                       : Monitor::Result::TIMEOUT;
 			}
 		}
 
 		void _charge_monitors() override
 		{
-			if (_monitors.charge_monitors())
+			if (!_execute_monitors_pending) {
+				_execute_monitors_pending = true;
 				Signal_transmitter(*_execute_monitors).submit();
+			}
 		}
 
 		/**

repos/libports/src/lib/libc/internal/monitor.h

@@ -48,20 +48,24 @@ class Libc::Monitor : Interface
 {
 	public:
 
+		enum class Result { COMPLETE, TIMEOUT };
+
 		struct Job;
 		struct Pool;
 
-		struct Function : Interface { virtual bool execute() = 0; };
+		enum class Function_result { COMPLETE, INCOMPLETE };
+
+		struct Function : Interface { virtual Function_result execute() = 0; };
 
 	protected:
 
-		virtual bool _monitor(Mutex &, Function &, uint64_t) = 0;
+		virtual Result _monitor(Mutex &, Function &, uint64_t) = 0;
 		virtual void _charge_monitors() = 0;
 
 	public:
 
 		/**
-		 * Block until monitored execution succeeds or timeout expires
+		 * Block until monitored execution completed or timeout expires
 		 *
 		 * The mutex must be locked when calling the monitor. It is released
 		 * during wait for completion and re-aquired before the function
@@ -70,15 +74,16 @@ class Libc::Monitor : Interface
 		 * Returns true if execution completed, false on timeout.
 		 */
 		template <typename FN>
-		bool monitor(Mutex &mutex, FN const &fn, uint64_t timeout_ms = 0)
+		Result monitor(Mutex &mutex, FN const &fn, uint64_t timeout_ms = 0)
 		{
 			struct _Function : Function
 			{
 				FN const &fn;
-				bool execute() override { return fn(); }
+				Function_result execute() override { return fn(); }
 				_Function(FN const &fn) : fn(fn) { }
 			} function { fn };
 
+			_charge_monitors();
 			return _monitor(mutex, function, timeout_ms);
 		}
 
@@ -103,7 +108,7 @@ struct Libc::Monitor::Job
 
 		virtual ~Job() { }
 
-		bool execute() { return _fn.execute(); }
+		bool execute() { return _fn.execute() == Function_result::COMPLETE; }
 
 		bool completed() const { return _blockade.woken_up(); }
 		bool expired()   const { return _blockade.expired(); }
@@ -117,43 +122,30 @@ struct Libc::Monitor::Pool
 {
 	private:
 
-		Registry<Job> _jobs;
+		Monitor       &_monitor;
-		Mutex         _mutex;
+		Registry<Job>  _jobs;
-
-		bool _execution_pending { false };
 
 	public:
 
+		Pool(Monitor &monitor) : _monitor(monitor) { }
+
+		/* called by monitor-user context */
 		void monitor(Mutex &mutex, Job &job)
 		{
 			Registry<Job>::Element element { _jobs, job };
 
 			mutex.release();
 
+			_monitor.charge_monitors();
+
 			job.wait_for_completion();
 
 			mutex.acquire();
 		}
 
-		bool charge_monitors()
+		/* called by the monitor context itself */
-		{
-			Mutex::Guard guard { _mutex };
-
-			bool const charged = !_execution_pending;
-			_execution_pending = true;
-			return charged;
-		}
-
 		void execute_monitors()
 		{
-			{
-				Mutex::Guard guard { _mutex };
-
-				if (!_execution_pending) return;
-
-				_execution_pending = false;
-			}
-
 			_jobs.for_each([&] (Job &job) {
 				if (!job.completed() && !job.expired() && job.execute()) {
 					job.complete();