hw: introduce non-blocking signal checking

* Introduces pending_signal syscall to check for new signals for the
  calling thread without blocking
* Implements pending_signal in the base-library specific for hw to use the
  new syscall

Fix #3217

repos/base-hw/include/kernel/interface.h

@@ -32,14 +32,15 @@ namespace Kernel
 	constexpr Call_arg call_id_kill_signal_context()      { return  6; }
 	constexpr Call_arg call_id_submit_signal()            { return  7; }
 	constexpr Call_arg call_id_await_signal()             { return  8; }
-	constexpr Call_arg call_id_cancel_next_await_signal() { return  9; }
-	constexpr Call_arg call_id_ack_signal()               { return 10; }
-	constexpr Call_arg call_id_print_char()               { return 11; }
-	constexpr Call_arg call_id_update_data_region()       { return 12; }
-	constexpr Call_arg call_id_update_instr_region()      { return 13; }
-	constexpr Call_arg call_id_ack_cap()                  { return 14; }
-	constexpr Call_arg call_id_delete_cap()               { return 15; }
-	constexpr Call_arg call_id_timeout()                  { return 16; }
+	constexpr Call_arg call_id_pending_signal()           { return  9; }
+	constexpr Call_arg call_id_cancel_next_await_signal() { return 10; }
+	constexpr Call_arg call_id_ack_signal()               { return 11; }
+	constexpr Call_arg call_id_print_char()               { return 12; }
+	constexpr Call_arg call_id_update_data_region()       { return 13; }
+	constexpr Call_arg call_id_update_instr_region()      { return 14; }
+	constexpr Call_arg call_id_ack_cap()                  { return 15; }
+	constexpr Call_arg call_id_delete_cap()               { return 16; }
+	constexpr Call_arg call_id_timeout()                  { return 17; }
 	constexpr Call_arg call_id_timeout_max_us()           { return 18; }
 	constexpr Call_arg call_id_time()                     { return 19; }
 
@@ -285,6 +286,25 @@ namespace Kernel
 		return call(call_id_await_signal(), receiver_id);
 	}
 
+
+	/**
+	 * Check for any pending signal of a context of a receiver the calling
+	 * thread relates to
+	 *
+	 * \param receiver_id  capability id of the targeted signal receiver
+	 *
+	 * \retval  0  suceeded
+	 * \retval -1  failed
+	 *
+	 * If this call returns 0, an instance of 'Signal::Data' is located at the
+	 * base of the callers UTCB.
+	 */
+	inline int pending_signal(capid_t const receiver_id)
+	{
+		return call(call_id_pending_signal(), receiver_id);
+	}
+
+
 	/**
 	 * Request to cancel the next signal blocking of a local thread
 	 *

repos/base-hw/src/core/kernel/thread.cc

@@ -464,6 +464,33 @@ void Thread::_call_await_signal()
 }
 
 
+void Thread::_call_pending_signal()
+{
+	/* lookup receiver */
+	Signal_receiver * const r = pd().cap_tree().find<Signal_receiver>(user_arg_1());
+	if (!r) {
+		Genode::warning(*this, ": cannot await, unknown signal receiver ",
+		                (unsigned)user_arg_1());
+		user_arg_0(-1);
+		return;
+	}
+
+	/* register handler at the receiver */
+	if (r->add_handler(this)) {
+		user_arg_0(-1);
+		return;
+	}
+
+	if (_state == AWAITS_SIGNAL) {
+		_cancel_blocking();
+		user_arg_0(-1);
+		return;
+	}
+
+	user_arg_0(0);
+}
+
+
 void Thread::_call_cancel_next_await_signal()
 {
 	/* kill the caller if the capability of the target thread is invalid */
@@ -631,6 +658,7 @@ void Thread::_call()
 	case call_id_kill_signal_context():      _call_kill_signal_context(); return;
 	case call_id_submit_signal():            _call_submit_signal(); return;
 	case call_id_await_signal():             _call_await_signal(); return;
+	case call_id_pending_signal():           _call_pending_signal(); return;
 	case call_id_cancel_next_await_signal(): _call_cancel_next_await_signal(); return;
 	case call_id_ack_signal():               _call_ack_signal(); return;
 	case call_id_print_char():               _call_print_char(); return;

repos/base-hw/src/core/kernel/thread.h

@@ -216,6 +216,7 @@ class Kernel::Thread
 		void _call_update_instr_region();
 		void _call_print_char();
 		void _call_await_signal();
+		void _call_pending_signal();
 		void _call_cancel_next_await_signal();
 		void _call_submit_signal();
 		void _call_ack_signal();

repos/base-hw/src/lib/base/signal_receiver.cc

@@ -129,9 +129,10 @@ void Signal_receiver::block_for_signal()
 		/* canceled */
 		return;
 	}
+
 	/* read signal data */
-	const void * const     utcb    = Thread::myself()->utcb()->data();
-	Signal::Data * const   data    = (Signal::Data *)utcb;
+	Signal::Data * const data =
+		(Signal::Data *)Thread::myself()->utcb()->data();
 	Signal_context * const context = data->context;
 
 	/**
@@ -145,11 +146,60 @@ void Signal_receiver::block_for_signal()
 		context->_pending     = true;
 		context->_curr_signal = Signal::Data(context, num);
 	}
+
 	/* end kernel-aided life-time management */
 	Kernel::ack_signal(Capability_space::capid(data->context->_cap));
 }
 
 
+Signal Signal_receiver::pending_signal()
+{
+	Lock::Guard contexts_lock_guard(_contexts_lock);
+	Signal::Data result;
+	_contexts.for_each_locked([&] (Signal_context &context) {
+
+		if (!context._pending) return;
+
+		_contexts.head(context._next);
+		context._pending     = false;
+		result               = context._curr_signal;
+		context._curr_signal = Signal::Data(0, 0);
+
+		Trace::Signal_received trace_event(context, result.num);
+		throw Context_ring::Break_for_each();
+	});
+	if (result.context) {
+		Lock::Guard lock_guard(result.context->_lock);
+		if (result.num == 0)
+			warning("returning signal with num == 0");
+
+		return result;
+	}
+
+	/* look for pending signals */
+	if (Kernel::pending_signal(Capability_space::capid(_cap)) != 0) {
+		throw Signal_not_pending();
+	}
+
+	/* read signal data */
+	Signal::Data * const data =
+		(Signal::Data *)Thread::myself()->utcb()->data();
+	Signal_context * const context = data->context;
+
+	{
+		/* update signal context */
+		Lock::Guard lock_guard(context->_lock);
+		context->_pending     = false;
+		context->_curr_signal = Signal::Data(context, data->num);
+		result                = context->_curr_signal;
+	}
+
+	/* end kernel-aided life-time management */
+	Kernel::ack_signal(Capability_space::capid(data->context->_cap));
+	return result;
+}
+
+
 void Signal_receiver::unblock_signal_waiter(Rpc_entrypoint &rpc_ep)
 {
 	Kernel::cancel_next_await_signal(native_thread_id(&rpc_ep));

repos/base/src/core/signal_receiver.cc

@@ -49,4 +49,7 @@ void Signal_receiver::block_for_signal()
 	sleep_forever();
 }
 
+Signal Signal_receiver::pending_signal() {
+	throw Signal_not_pending(); }
+
 void Signal_receiver::local_submit(Signal::Data) { ASSERT_NEVER_CALLED; }

repos/base/src/lib/base/signal.cc

@@ -235,6 +235,42 @@ void Signal_receiver::block_for_signal()
 	_signal_available.down();
 }
 
+Signal Signal_receiver::pending_signal()
+{
+	Lock::Guard contexts_lock_guard(_contexts_lock);
+	Signal::Data result;
+	_contexts.for_each_locked([&] (Signal_context &context) {
+
+		if (!context._pending) return;
+
+		_contexts.head(context._next);
+		context._pending     = false;
+		result               = context._curr_signal;
+		context._curr_signal = Signal::Data(0, 0);
+
+		Trace::Signal_received trace_event(context, result.num);
+		throw Context_ring::Break_for_each();
+	});
+	if (result.context) {
+		Lock::Guard lock_guard(result.context->_lock);
+		if (result.num == 0)
+			warning("returning signal with num == 0");
+
+		return result;
+	}
+
+	/*
+	 * Normally, we should never arrive at this point because that would
+	 * mean, the '_signal_available' semaphore was increased without
+	 * registering the signal in any context associated to the receiver.
+	 *
+	 * However, if a context gets dissolved right after submitting a
+	 * signal, we may have increased the semaphore already. In this case
+	 * the signal-causing context is absent from the list.
+	 */
+	throw Signal_not_pending();
+}
+
 
 void Signal_receiver::unblock_signal_waiter(Rpc_entrypoint &)
 {

repos/base/src/lib/base/signal_common.cc

@@ -159,43 +159,6 @@ Signal Signal_receiver::wait_for_signal()
 }
 
 
-Signal Signal_receiver::pending_signal()
-{
-	Lock::Guard contexts_lock_guard(_contexts_lock);
-	Signal::Data result;
-	_contexts.for_each_locked([&] (Signal_context &context) {
-
-		if (!context._pending) return;
-
-		_contexts.head(context._next);
-		context._pending     = false;
-		result               = context._curr_signal;
-		context._curr_signal = Signal::Data(0, 0);
-
-		Trace::Signal_received trace_event(context, result.num);
-		throw Context_ring::Break_for_each();
-	});
-	if (result.context) {
-		Lock::Guard lock_guard(result.context->_lock);
-		if (result.num == 0)
-			warning("returning signal with num == 0");
-
-		return result;
-	}
-
-	/*
-	 * Normally, we should never arrive at this point because that would
-	 * mean, the '_signal_available' semaphore was increased without
-	 * registering the signal in any context associated to the receiver.
-	 *
-	 * However, if a context gets dissolved right after submitting a
-	 * signal, we may have increased the semaphore already. In this case
-	 * the signal-causing context is absent from the list.
-	 */
-	throw Signal_not_pending();
-}
-
-
 Signal_receiver::~Signal_receiver()
 {
 	Lock::Guard contexts_lock_guard(_contexts_lock);