libc: dispatch pending signals at selective points

repos/base/include/base/entrypoint.h

@@ -118,6 +118,7 @@ class Genode::Entrypoint : Genode::Noncopyable
 		void _defer_signal(Signal &sig);
 		void _process_deferred_signals();
 		void _process_incoming_signals();
+		bool _wait_and_dispatch_one_io_signal(bool dont_block);
 
 		Constructible<Signal_proxy_thread> _signal_proxy_thread;
 
@@ -180,7 +181,21 @@ class Genode::Entrypoint : Genode::Noncopyable
 		 *     receiver belongs to the calling entrypoint. Alternatively,
 		 *     remove it.
 		 */
-		void wait_and_dispatch_one_io_signal();
+		void wait_and_dispatch_one_io_signal()
+		{
+			_wait_and_dispatch_one_io_signal(false);
+		}
+
+		/**
+		 * Dispatch single pending I/O-level signal (non-blocking)
+		 *
+		 * \return true if a pending signal was dispatched, false if no signal
+		 *         was pending
+		 */
+		bool dispatch_pending_io_signal()
+		{
+			return _wait_and_dispatch_one_io_signal(true);
+		}
 
 		/**
 		 * Return RPC entrypoint

repos/base/lib/symbols/ld

@@ -59,7 +59,7 @@ _ZN6Genode10Entrypoint16_dispatch_signalERNS_6SignalE T
 _ZN6Genode10Entrypoint16schedule_suspendEPFvvES2_ T
 _ZN6Genode10Entrypoint22Signal_proxy_component6signalEv T
 _ZN6Genode10Entrypoint25_process_incoming_signalsEv T
-_ZN6Genode10Entrypoint31wait_and_dispatch_one_io_signalEv T
+_ZN6Genode10Entrypoint32_wait_and_dispatch_one_io_signalEb T
 _ZN6Genode10Entrypoint6manageERNS_22Signal_dispatcher_baseE T
 _ZN6Genode10Entrypoint8dissolveERNS_22Signal_dispatcher_baseE T
 _ZN6Genode10EntrypointC1ERNS_3EnvE T

repos/base/src/lib/base/entrypoint.cc

@@ -172,7 +172,7 @@ void Entrypoint::_process_incoming_signals()
 }
 
 
-void Entrypoint::wait_and_dispatch_one_io_signal()
+bool Entrypoint::_wait_and_dispatch_one_io_signal(bool const dont_block)
 {
 	for (;;) {
 
@@ -198,6 +198,11 @@ void Entrypoint::wait_and_dispatch_one_io_signal()
 
 		} catch (Signal_receiver::Signal_not_pending) {
 			_signal_pending_lock.unlock();
+			if (dont_block) {
+				/* indicate that we leave wait_and_dispatch_one_io_signal */
+				cmpxchg(&_signal_recipient, ENTRYPOINT, NONE);
+				return false;
+			}
 			_sig_rec->block_for_signal();
 		}
 	}
@@ -212,6 +217,8 @@ void Entrypoint::wait_and_dispatch_one_io_signal()
 			                                   &Entrypoint::_handle_deferred_signals);
 		Signal_transmitter(*_deferred_signal_handler).submit();
 	}
+
+	return true;
 }
 
 

repos/libports/src/lib/libc/task.cc

@@ -389,7 +389,8 @@ struct Libc::Kernel
 
 		jmp_buf _kernel_context;
 		jmp_buf _user_context;
-		bool    _valid_user_context = false;
+		bool    _valid_user_context          = false;
+		bool    _dispatch_pending_io_signals = false;
 
 		Genode::Thread &_myself { *Genode::Thread::myself() };
 
@@ -566,7 +567,7 @@ struct Libc::Kernel
 			}
 
 			/*
-			 * During the supension of the application code a nested
+			 * During the suspension of the application code a nested
 			 * Libc::with_libc() call took place, which will be executed
 			 * before returning to the first Libc::with_libc() call.
 			 */
@@ -624,7 +625,13 @@ struct Libc::Kernel
 			/* _setjmp() returned after _longjmp() - user context suspended */
 
 			while ((!_app_returned) && (!_suspend_scheduled)) {
-				_env.ep().wait_and_dispatch_one_io_signal();
+				if (_dispatch_pending_io_signals) {
+					/* dispatch pending signals but don't block */
+					while (_env.ep().dispatch_pending_io_signal()) ;
+				} else {
+					/* block for signals */
+					_env.ep().wait_and_dispatch_one_io_signal();
+				}
 
 				if (_resume_main_once && !_setjmp(_kernel_context))
 					_switch_to_user();
@@ -686,6 +693,21 @@ struct Libc::Kernel
 			                       : _pthreads.suspend_myself(check, timeout_ms);
 		}
 
+		void dispatch_pending_io_signals()
+		{
+			if (!_main_context()) return;
+
+			if (!_setjmp(_user_context)) {
+				_valid_user_context          = true;
+				_dispatch_pending_io_signals = true;
+				_resume_main_once            = true; /* afterwards resume main */
+				_switch_to_kernel();
+			} else {
+				_valid_user_context          = false;
+				_dispatch_pending_io_signals = false;
+			}
+		}
+
 		unsigned long current_time()
 		{
 			return _timer_accessor.timer().curr_time();
@@ -812,6 +834,13 @@ unsigned long Libc::suspend(Suspend_functor &s, unsigned long timeout_ms)
 	return kernel->suspend(s, timeout_ms);
 }
 
+
+void Libc::dispatch_pending_io_signals()
+{
+	kernel->dispatch_pending_io_signals();
+}
+
+
 unsigned long Libc::current_time()
 {
 	return kernel->current_time();

repos/libports/src/lib/libc/task.h

@@ -46,6 +46,8 @@ namespace Libc {
 	struct Suspend_functor { virtual bool suspend() = 0; };
 	unsigned long suspend(Suspend_functor &, unsigned long timeout_ms = 0UL);
 
+	void dispatch_pending_io_signals();
+
 	/**
 	 * Get time since startup in ms
 	 */

repos/libports/src/lib/libc/vfs_plugin.cc

@@ -446,6 +446,8 @@ ssize_t Libc::Vfs_plugin::write(Libc::File_descriptor *fd, const void *buf,
 ssize_t Libc::Vfs_plugin::read(Libc::File_descriptor *fd, void *buf,
                                ::size_t count)
 {
+	Libc::dispatch_pending_io_signals();
+
 	typedef Vfs::File_io_service::Read_result Result;
 
 	Vfs::Vfs_handle *handle = vfs_handle(fd);