[kernel] Add object_wait_many syscall

Add the object_wait_many syscall to allow programs to wait for signals
on multiple objects at once. Also removed the object argument to
thread::wait_on_signals, which does nothing with it. That information is
saved in the thread being in the object's blocked threads list.

src/kernel/log.cpp

@@ -75,7 +75,7 @@ logger_task()
 		if (!g_logger.has_log()) {
 			sys.deassert_signal(j6_signal_system_has_log);
 			sys.add_blocked_thread(&self);
-			self.wait_on_signals(&sys, j6_signal_system_has_log);
+			self.wait_on_signals(j6_signal_system_has_log);
 		}
 	}
 }

src/kernel/objects/kobject.cpp

@@ -50,13 +50,11 @@ void
 kobject::notify_signal_observers()
 {
 	size_t i = 0;
-	bool readied = false;
 	while (i < m_blocked_threads.count()) {
 		thread *t = m_blocked_threads[i];
 
 		if (t->wake_on_signals(this, m_signals)) {
 			m_blocked_threads.remove_swap_at(i);
-			readied = true;
 		} else {
 			++i;
 		}

src/kernel/objects/thread.cpp

@@ -48,7 +48,7 @@ thread & thread::current() { return *current_cpu().thread; }
 inline void schedule_if_current(thread *t) { if (t == current_cpu().thread) scheduler::get().schedule(); }
 
 void
-thread::wait_on_signals(kobject *obj, j6_signal_t signals)
+thread::wait_on_signals(j6_signal_t signals)
 {
 	m_wait_type = wait_type::signal;
 	m_wait_data = signals;

src/kernel/objects/thread.h

@@ -74,10 +74,9 @@ public:
 	/// \arg p  The new thread priority
 	inline void set_priority(uint8_t p) { if (!constant()) m_tcb.priority = p; }
 
-	/// Block the thread, waiting on the given object's signals.
-	/// \arg obj     Object to wait on
+	/// Block the thread, waiting an object's signals.
 	/// \arg signals Mask of signals to wait for
-	void wait_on_signals(kobject *obj, j6_signal_t signals);
+	void wait_on_signals(j6_signal_t signals);
 
 	/// Block the thread, waiting for a given clock value
 	/// \arg t  Clock value to wait for
@@ -114,6 +113,9 @@ public:
 	/// Get the current blocking opreation's wait data
 	uint64_t get_wait_data() const { return m_wait_data; }
 
+    /// Get the current blocking operation's wait ojbect (as a handle)
+	j6_koid_t get_wait_object() const { return m_wait_obj; }
+
 	inline bool has_state(state s) const {
 		return static_cast<uint8_t>(m_state) & static_cast<uint8_t>(s);
 	}

src/kernel/syscalls/object.cpp

@@ -37,7 +37,7 @@ object_wait(j6_handle_t handle, j6_signal_t mask, j6_signal_t *sigs)
 
 	thread &th = thread::current();
 	obj->add_blocked_thread(&th);
-	th.wait_on_signals(obj, mask);
+	th.wait_on_signals(mask);
 
 	j6_status_t result = th.get_wait_result();
 	if (result == j6_status_ok) {
@@ -46,6 +46,55 @@ object_wait(j6_handle_t handle, j6_signal_t mask, j6_signal_t *sigs)
 	return result;
 }
 
+j6_status_t
+object_wait_many(j6_handle_t *handles, uint32_t count, j6_signal_t mask, j6_handle_t *handle, j6_signal_t *sigs)
+{
+    kutil::vector<kobject*> objects {count};
+
+    for (unsigned i = 0; i < count; ++i) {
+        j6_handle_t h = handles[i];
+        if (h == j6_handle_invalid)
+            continue;
+
+        kobject *obj = get_handle<kobject>(h);
+        if (!obj)
+            return j6_err_invalid_arg;
+
+        j6_signal_t current = obj->signals();
+        if ((current & mask) != 0) {
+            *sigs = current;
+            *handle = h;
+            return j6_status_ok;
+        }
+
+        objects.append(obj);
+    }
+
+	thread &th = thread::current();
+    for (auto *obj : objects)
+        obj->add_blocked_thread(&th);
+
+	th.wait_on_signals(mask);
+
+	j6_status_t result = th.get_wait_result();
+	if (result != j6_status_ok)
+        return result;
+
+    *handle = j6_handle_invalid;
+    *sigs = th.get_wait_data();
+    j6_koid_t koid = th.get_wait_object();
+    for (unsigned i = 0; i < count; ++i) {
+        if (koid == objects[i]->koid())
+            *handle = handles[i];
+        else
+            objects[i]->remove_blocked_thread(&th);
+    }
+
+    kassert(*handle != j6_handle_invalid,
+        "Somehow woke on a handle that was not waited on");
+    return j6_status_ok;
+}
+
 j6_status_t
 object_signal(j6_handle_t handle, j6_signal_t signals)
 {

src/kernel/syscalls/thread.cpp

@@ -40,7 +40,7 @@ j6_status_t
 thread_pause()
 {
 	thread &th = thread::current();
-	th.wait_on_signals(&th, -1ull);
+	th.wait_on_signals(-1ull);
 	return j6_status_ok;
 }