[Blockable] Set affinity on block

.gitlab-ci.yml

@@ -163,6 +163,10 @@ clang-tidy:
   variables:
     EMPER_WAKEUP_SEMAPHORE_IMPLEMENTATION: "locked"
 
+.set-affinity-on-block:
+  variables:
+    EMPER_SET_AFFINITY_ON_BLOCK: 'true'
+
 test-gcc:
   extends:
     - .test
@@ -258,3 +262,8 @@ test-locked-wakeup-semaphore:
   extends:
     - .test
     - .locked-wakeup-semaphore
+
+test-set-affinity-on-block:
+  extends:
+    - .test
+    - .set-affinity-on-block

emper/Blockable.hpp

@@ -24,8 +24,31 @@ class Blockable : public Logger<logSubsystem> {
 
 	workeraffinity_t* affinity = nullptr;
 
+	// It would be OK to not initialize this member since it is only set
+	// and read after affinity has been set to a non nullptr
+	// value. However, if we do not set it, then clang-tidy complains
+	// about clang-analyzer-optin.cplusplus.UninitializedObject.
+	workeraffinity_t affinity_buffer = Fiber::NOT_AFFINE;
+
 	Blockable(Runtime& runtime) : runtime(runtime), contextManager(runtime.getContextManager()) {}
 
+	void maybeSetAffinity() {
+		if constexpr (!emper::SET_AFFINITY_ON_BLOCK) return;
+
+		// TODO: At some point we may want to have something like
+		// Runtime::isAffinityCapable() and return here if it is
+		// not. Although I am not sure if it is worth the overhead.
+
+		auto* currentFiber = Context::getCurrentFiber();
+		auto* affinity = currentFiber->getAffinityBuffer();
+		if (affinity) {
+			this->affinity = affinity;
+		} else {
+			affinity_buffer = Runtime::getWorkerId();
+			this->affinity = &affinity_buffer;
+		}
+	}
+
 	// Older clang-tidy versions show a
 	// performance-unnecessary-value-param, newer versions do not show
 	// this error if std::move() is used (as we do).
@@ -36,6 +59,8 @@ class Blockable : public Logger<logSubsystem> {
 
 		LOGD("block() blockedContext is " << Context::getCurrentContext());
 
+		maybeSetAffinity();
+
 		if constexpr (emper::BLOCKED_CONTEXT_SET) {
 			blockedContexts.insert(Context::getCurrentContext());
 		}

emper/Emper.hpp

@@ -113,4 +113,13 @@ enum class IoCompleterBehavior {
 
 static const enum IoCompleterBehavior IO_COMPLETER_BEHAVIOR =
 		IoCompleterBehavior::EMPER_IO_COMPLETER_BEHAVIOR;
+
+static const bool SET_AFFINITY_ON_BLOCK =
+#ifdef EMPER_SET_AFFINITY_ON_BLOCK
+		true
+#else
+		false
+#endif
+		;
+
 }	 // namespace emper

emper/Fiber.hpp

@@ -95,6 +95,8 @@ class ALIGN_TO_CACHE_LINE Fiber : public Logger<LogSubsystem::F> {
 		return --referenceCounter;
 	}
 
+	template <LogSubsystem>
+	friend class Blockable;
 	friend class adt::MpscQueue<Fiber>;
 	friend class Scheduler;
 	friend class Dispatcher;

meson_options.txt

@@ -129,3 +129,9 @@ option(
   choices: ['schedule', 'maybe_wakeup'],
   value: 'schedule',
 )
+option(
+  'set_affinity_on_block',
+  type: 'boolean',
+  value: false,
+  description: 'Set the affinity when blocking',
+)