Remove exceptions from Cpu_session interface

The 'Thread_creation_failed' error is now reflected as
'Thread::Start_result' return value. This change also removes the
use of 'Invalid_thread' within core as this exception is an alias
of Cpu_session::Thread_creation_failed.

Issue #5245

repos/base/src/core/cpu_session_component.cc

@@ -25,73 +25,66 @@
 using namespace Core;
 
 
-Thread_capability Cpu_session_component::create_thread(Capability<Pd_session> pd_cap,
-                                                       Name const &name,
-                                                       Affinity::Location affinity,
-                                                       Weight weight,
-                                                       addr_t utcb)
+Cpu_session::Create_thread_result
+Cpu_session_component::create_thread(Capability<Pd_session> pd_cap,
+                                     Name const &name, Affinity::Location affinity,
+                                     Weight weight, addr_t utcb)
 {
-	Trace::Thread_name thread_name(name.string());
+	if (!try_withdraw(Ram_quota{_utcb_quota_size()}))
+		return Create_thread_error::OUT_OF_RAM;
 
-	withdraw(Ram_quota{_utcb_quota_size()});
+	if (weight.value == 0) {
+		warning("Thread ", name, ": Bad weight 0, using default weight instead.");
+		weight = Weight();
+	}
+	if (weight.value > QUOTA_LIMIT) {
+		warning("Thread ", name, ": Oversized weight ", weight.value, ", using limit instead.");
+		weight = Weight(QUOTA_LIMIT);
+	}
 
-	try {
+	Mutex::Guard thread_list_lock_guard(_thread_list_lock);
 
-		Cpu_thread_component *thread = 0;
+	Create_thread_result result = Create_thread_error::DENIED;
 
-		if (weight.value == 0) {
-			warning("Thread ", name, ": Bad weight 0, using default weight instead.");
-			weight = Weight();
-		}
-		if (weight.value > QUOTA_LIMIT) {
-			warning("Thread ", name, ": Oversized weight ", weight.value, ", using limit instead.");
-			weight = Weight(QUOTA_LIMIT);
+	_incr_weight(weight.value);
+
+	_thread_ep.apply(pd_cap, [&] (Pd_session_component *pd) {
+
+		if (!pd) {
+			error("create_thread: invalid PD argument");
+			return;
 		}
 
-		Mutex::Guard thread_list_lock_guard(_thread_list_lock);
+		Mutex::Guard slab_lock_guard(_thread_alloc_lock);
 
-		/*
-		 * Create thread associated with its protection domain
-		 */
-		auto create_thread_lambda = [&] (Pd_session_component *pd) {
-			if (!pd) {
-				error("create_thread: invalid PD argument");
-				throw Thread_creation_failed();
-			}
-
-			Mutex::Guard slab_lock_guard(_thread_alloc_lock);
-			thread = new (&_thread_alloc)
+		try {
+			Cpu_thread_component &thread = *new (&_thread_alloc)
 				Cpu_thread_component(
 					cap(), _thread_ep, _pager_ep, *pd, _trace_control_area,
 					_trace_sources, weight, _weight_to_quota(weight.value),
-					_thread_affinity(affinity), _label, thread_name,
+					_thread_affinity(affinity), _label, name,
 					_priority, utcb);
-		};
 
-		try {
-			_incr_weight(weight.value);
-			_thread_ep.apply(pd_cap, create_thread_lambda);
-		} catch (Allocator::Out_of_memory) {
-			_decr_weight(weight.value);
-			throw Out_of_ram();
-		} catch (Native_capability::Reference_count_overflow) {
-			_decr_weight(weight.value);
-			throw Thread_creation_failed();
-		} catch (...) {
-			_decr_weight(weight.value);
-			throw;
+			if (!thread.valid()) {
+				destroy(_thread_alloc, &thread);
+				return;
+			}
+
+			thread.session_exception_sigh(_exception_sigh);
+
+			_thread_list.insert(&thread);
+			result = thread.cap();
 		}
+		catch (Out_of_ram)  { result = Create_thread_error::OUT_OF_RAM;  }
+		catch (Out_of_caps) { result = Create_thread_error::OUT_OF_CAPS; }
+		catch (...)         { result = Create_thread_error::DENIED;      }
+	});
 
-		thread->session_exception_sigh(_exception_sigh);
-
-		_thread_list.insert(thread);
-
-		return thread->cap();
-
-	} catch (...) {
+	if (result.failed()) {
+		_decr_weight(weight.value);
 		replenish(Ram_quota{_utcb_quota_size()});
-		throw;
 	}
+	return result;
 }
 
 

repos/base/src/core/include/account.h

@@ -192,6 +192,17 @@ class Core::Account
 			_quota_guard.withdraw(amount);
 		}
 
+		/**
+		 * Withdraw quota from account
+		 *
+		 * \return true if withdrawal of 'amount' succeeded
+		 */
+		[[nodiscard]] bool try_withdraw(UNIT amount)
+		{
+			Mutex::Guard guard(_mutex);
+			return _quota_guard.try_withdraw(amount);
+		}
+
 		/**
 		 * Replenish quota to account
 		 *

repos/base/src/core/include/cpu_session_component.h

@@ -166,8 +166,8 @@ class Core::Cpu_session_component : public  Session_object<Cpu_session>,
 		 ** CPU session interface **
 		 ***************************/
 
-		Thread_capability create_thread(Capability<Pd_session>, Name const &,
-		                                Affinity::Location, Weight, addr_t) override;
+		Create_thread_result create_thread(Capability<Pd_session>, Name const &,
+		                                   Affinity::Location, Weight, addr_t) override;
 		void kill_thread(Thread_capability) override;
 		void exception_sigh(Signal_context_capability) override;
 		Affinity::Space affinity_space() const override;

repos/base/src/core/include/cpu_thread_component.h

@@ -55,9 +55,7 @@ class Core::Cpu_thread_component : public  Rpc_object<Cpu_thread>,
 
 		bool _bind_to_pd(Pd_session_component &pd)
 		{
-			if (!pd.bind_thread(_platform_thread))
-				throw Cpu_session::Thread_creation_failed();
-			return true;
+			return pd.bind_thread(_platform_thread);
 		}
 
 		/**
@@ -183,6 +181,8 @@ class Core::Cpu_thread_component : public  Rpc_object<Cpu_thread>,
 			_address_space_region_map.remove_client(_rm_client);
 		}
 
+		bool valid() const { return _bound_to_pd; };
+
 
 		/********************************************
 		 ** Trace::Source::Info_accessor interface **

repos/base/src/core/include/irq_object.h

@@ -43,7 +43,7 @@ class Core::Irq_object : public Thread
 		void sigh(Signal_context_capability cap) { _sig_cap = cap; }
 		void ack_irq() { _sync_ack.wakeup(); }
 
-		void start() override;
+		Start_result start() override;
 };
 
 #endif /* _CORE__INCLUDE__IRQ_OBJECT_H_ */

repos/base/src/core/include/pager.h

@@ -30,8 +30,6 @@
 
 namespace Core {
 
-	typedef Cpu_session::Thread_creation_failed Invalid_thread;
-
 	/**
 	 * Special server object for paging
 	 *
@@ -84,8 +82,6 @@ class Core::Pager_object : public Object_pool<Pager_object>::Entry
 		 * Constructor
 		 *
 		 * \param location  affinity of paged thread to physical CPU
-		 *
-		 * \throw Invalid_thread
 		 */
 		Pager_object(Cpu_session_capability cpu_sesion,
 		             Thread_capability thread,