meso: Implement ConnectLight

mesosphere/source/processes/KClientPort.cpp

@@ -2,6 +2,7 @@
 #include <mesosphere/threading/KScopedCriticalSection.hpp>
 #include <mesosphere/threading/KThread.hpp>
 #include <mesosphere/core/KCoreContext.hpp>
+#include <mesosphere/core/make_object.hpp>
 
 namespace mesosphere
 {
@@ -14,7 +15,30 @@ KClientPort::~KClientPort()
 
 bool KClientPort::IsSignaled() const
 {
-    return false; // TODO
+    return numSessions.load() < maxSessions;
+}
+
+std::tuple<Result, SharedPtr<KLightClientSession>> KClientPort::ConnectLight()
+{
+    using RetType = std::tuple<Result, SharedPtr<KLightClientSession>>;
+    // Official kernel first checks reslimit then session max count. We will do the opposite.
+    int curCount = numSessions.load();
+    while (curCount < maxSessions || !numSessions.compare_exchange_weak(curCount, curCount + 1));
+
+    if (curCount >= maxSessions) {
+        return RetType{ResultKernelOutOfSessions(), nullptr};
+    }
+
+    auto [res, serverSession, clientSession] = MakeObject<KLightSession>(parent.get());
+    if (res.IsSuccess()) {
+        serverSession.detach(); // Lifetime is now managed my KServerPort session list
+        return RetType{ResultSuccess(), clientSession};
+    } else {
+        if (numSessions.fetch_sub(1) == maxSessions) {
+            NotifyWaiters();
+        }
+        return RetType{res, nullptr};
+    }
 }
 
 }