emper/Context.hpp

@@ -106,6 +106,14 @@ class EMPER_CONTEXT_ALIGNAS Context : Logger<LogSubsystem::C> {
 	static auto calcBos(char* context) -> void*;
 	auto calcBos() -> void*;
 
+	/*
+	 * Used by ContextManager to re-initialize a cached unused context.
+	 */
+	inline void reinit() {
+		currentFiber = nullptr;
+		savedStackpointer = const_cast<void*>(alphaFunctionIpLocation);
+	}
+
  public:
 	Context(func_t mainFunction);
 

emper/ContextManager.cpp

@@ -31,6 +31,7 @@ auto ContextManager::getFreeContext() -> Context* {
 	}
 
 	auto* context = static_cast<Context*>(memory);
+	context->reinit();
 	if constexpr (emper::STATS_STACK_USAGE == emper::StatsStackUsage::accurate) {
 		// If we want accurate stack-usage stats, then we need to re-mark
 		// the stack if we got the memory from the memory manager but if
@@ -45,7 +46,7 @@ void ContextManager::putFreeContext(Context* context) {
 		context->recordStackUsage();
 	}
 
-	if constexpr (!emper::CONTEXT_MANAGER_WITH_MEMORY_MANAGER) {
+	if constexpr (emper::CONTEXT_MANAGER_WITH_MEMORY_MANAGER) {
 		putMemory(context);
 	} else {
 		delete context;
@@ -72,34 +73,15 @@ void ContextManager::start() {
 		return;
 	}
 
+	Context* freeContext = nullptr;
 	if constexpr (emper::CONTINUATION_STEALING) {
 		Fibril::tryResumeFibril(fibrilResumeValue);
 
-		// The code below only needs to be executed if we did a long jmp
-		// before. But optimizing for it is not worth it.  If we longjmp
-		// and can not resume the Fibril and we where not on the initial
-		// context of the Fibril, then we need to take care to recycle the
-		// context.
-		Context* currentContext = Context::getCurrentContext();
-		if (currentContext) {
-			// If we would simply call currentContext->start() here, then we
-			// would jump to an invalid address. The reason is that as soon as
-			// the Context::kickoff() is executed, the alpha function address,
-			// which was just popped of the stack, will be potentially
-			// overriden by a stack push operation. And such operations are
-			// very likely. Instead we simply free the current context here,
-			// so that it is re-initialized later on.
-
-			// TODO: Adjust the assembly to not use 'ret' to reach the
-			// kickoff function, but instead jmp. This would not destroy the
-			// kickoff's function pointer on the stack, and we could call
-			// currentContext->start() here. This would print a small
-			// performance gain.
-			putFreeContext(currentContext);
-		}
+		freeContext = Context::getCurrentContext();
 	}
 
-	Context* freeContext = getFreeContext();
+	if (!freeContext) freeContext = getFreeContext();
+
 	freeContext->start();
 }
 
@@ -147,6 +129,7 @@ void ContextManager::discardAndResume(Context* context) {
 	// the end of its dispatch loop, and hence we need to ensure that
 	// its fiber is recycled.
 	AbstractFiber* currentFiber = contextToFree->getFiber();
+	assert(currentFiber);
 	runtime.dispatcher.recycle(currentFiber);
 
 	contextToFree->discardAndResume(context);