Introduce PushBottomResult as return value of wsqueue's pushBottom()

This result also contains the observed queue size at the moment of the
push.

emper/lib/adt/LockedQueue.hpp

@@ -8,6 +8,7 @@
 
 #include "Common.hpp"
 #include "StealingResult.hpp"
+#include "lib/adt/PushBottomResult.hpp"
 
 // Forward declaration, declared and defined in Fibril.hpp.
 namespace emper {
@@ -41,14 +42,19 @@ class LockedQueue {
 		return deque.size();
 	}
 
-	auto pushBottom(const I item) -> bool {
+	auto pushBottom(const I item) -> PushBottomResult {
+		bool pushed = true;
 		std::lock_guard<std::mutex> lock(queue_mutex);
 
-		if (deque.size() == SIZE) return false;
+		if (deque.size() == SIZE) {
+			pushed = false;
+			goto out;
+		}
 
 		deque.push_back(item);
 
-		return true;
+	out:
+		return PushBottomResult{pushed, deque.size()};
 	}
 
 	template <const int maxRetries>

emper/lib/adt/PushBottomResult.hpp

+// SPDX-License-Identifier: LGPL-3.0-or-later
+// Copyright © 2022 Florian Schmaus
+#pragma once
+
+namespace adt {
+
+struct PushBottomResult {
+	const bool pushed;
+	const uint64_t size;
+
+	operator bool() const { return pushed; }
+};
+
+}	 // namespace adt

emper/lib/adt/WsClQueue.hpp

 // SPDX-License-Identifier: LGPL-3.0-or-later
-// Copyright © 2020 Florian Schmaus
+// Copyright © 2020-2022 Florian Schmaus
 #pragma once
 
 #include <atomic>
@@ -7,6 +7,7 @@
 
 #include "Common.hpp"
 #include "StealingResult.hpp"
+#include "lib/adt/PushBottomResult.hpp"
 
 namespace adt {
 
@@ -47,7 +48,7 @@ class WsClQueue {
 	WsClQueue() : bottom(1), top(1) {}
 	// TODO: Decide what to do regarding the following suppressed lint.
 	// NOLINTNEXTLINE(readability-avoid-const-params-in-decls)
-	auto pushBottom(const PAYLOAD item) -> bool;
+	auto pushBottom(const PAYLOAD item) -> PushBottomResult;
 	template <const int maxRetries>
 	auto popTop(PAYLOAD *item) -> emper::StealingResult;
 	auto popBottom(PAYLOAD *item) -> bool;
@@ -60,8 +61,14 @@ class WsClQueue {
 };
 
 template <typename PAYLOAD, const uintptr_t CAPACITY>
-auto WsClQueue<PAYLOAD, CAPACITY>::pushBottom(const PAYLOAD item) -> bool {
-	if (isFull()) return false;
+auto WsClQueue<PAYLOAD, CAPACITY>::pushBottom(const PAYLOAD item) -> PushBottomResult {
+	bool pushed = true;
+	uint64_t newSize =
+			bottom.load(std::memory_order_relaxed) - top.load(std::memory_order_relaxed) + 1;
+	if (newSize > CAPACITY) {
+		pushed = false;
+		goto out;
+	}
 
 	queue[bottom % CAPACITY] = item;
 
@@ -69,7 +76,9 @@ auto WsClQueue<PAYLOAD, CAPACITY>::pushBottom(const PAYLOAD item) -> bool {
 	atomic_thread_fence(std::memory_order_release);
 
 	++bottom;
-	return true;
+
+out:
+	return PushBottomResult{pushed, newSize};
 }
 
 template <typename PAYLOAD, const uintptr_t CAPACITY>

emper/lib/adt/WsClV2Queue.hpp

 // SPDX-License-Identifier: LGPL-3.0-or-later
-// Copyright © 2020 Florian Schmaus
+// Copyright © 2020-2022 Florian Schmaus
 #pragma once
 
 #include <atomic>
@@ -7,6 +7,7 @@
 
 #include "Common.hpp"
 #include "StealingResult.hpp"
+#include "lib/adt/PushBottomResult.hpp"
 
 namespace adt {
 
@@ -51,7 +52,7 @@ class WsClV2Queue {
 	// an underflow if bottom is '0'. The paper's queue uses Java
 	// 'long' for bottom and top and is thus safe since it's signed.
 	WsClV2Queue() : top(1) {}
-	auto pushBottom(ITEM_TYPE item) -> bool;
+	auto pushBottom(ITEM_TYPE item) -> PushBottomResult;
 	auto popBottom(ITEM_TYPE *item) -> bool;
 	template <const int maxRetries>
 	auto popTop(ITEM_TYPE *item) -> emper::StealingResult;
@@ -64,9 +65,13 @@ class WsClV2Queue {
 };
 
 template <typename ITEM_TYPE, const uintptr_t CAPACITY>
-auto WsClV2Queue<ITEM_TYPE, CAPACITY>::pushBottom(const ITEM_TYPE item) -> bool {
+auto WsClV2Queue<ITEM_TYPE, CAPACITY>::pushBottom(const ITEM_TYPE item) -> PushBottomResult {
+	bool pushed = true;
 	// Check if queue is full.
-	if (isFull()) return false;
+	if (isFull()) {
+		pushed = false;
+		goto out;
+	}
 
 	queue[bottom % CAPACITY] = item;
 
@@ -76,7 +81,8 @@ auto WsClV2Queue<ITEM_TYPE, CAPACITY>::pushBottom(const ITEM_TYPE item) -> bool
 	// Write fence / memory barrier
 	atomic_thread_fence(std::memory_order_release);
 
-	return true;
+out:
+	return PushBottomResult{pushed, bottom - top};
 }
 
 template <typename ITEM_TYPE, const uintptr_t CAPACITY>

emper/strategies/AbstractWorkStealingScheduler.cpp

@@ -23,6 +23,7 @@
 #include "Worker.hpp"
 #include "emper-common.h"	 // for workerid_t
 #include "io/IoContext.hpp"
+#include "lib/adt/PushBottomResult.hpp"
 #include "strategies/AbstractWorkStealingStrategy.hpp"
 #include "strategies/AbstractWorkStealingWorkerStats.hpp"
 
@@ -51,7 +52,7 @@ AbstractWorkStealingScheduler::AbstractWorkStealingScheduler(Runtime& runtime,
 }
 
 void AbstractWorkStealingScheduler::scheduleViaWorkStealing(Fiber& fiber) {
-	bool pushed = queue.pushBottom(&fiber);
+	auto pushed = queue.pushBottom(&fiber);
 	if (unlikely(!pushed)) {
 		if constexpr (emper::OVERFLOW_QUEUE) {
 			enqueueInAnywhereQueue(fiber);
@@ -61,7 +62,7 @@ void AbstractWorkStealingScheduler::scheduleViaWorkStealing(Fiber& fiber) {
 			ABORT("Could not push fiber " << &fiber << " into queue");
 		}
 	} else if constexpr (emper::STATS) {
-		uint64_t queueLength = queue.usedSlots();
+		uint64_t queueLength = pushed.size;
 		awss::stats.recordScheduledToLocalAndQueueLength(queueLength);
 	}
 
@@ -289,6 +290,10 @@ auto AbstractWorkStealingScheduler::pushBottom(AbstractFiber& fiber) -> bool {
 	auto pushed = queue.pushBottom(&fiber);
 	if (pushed) [[likely]] {
 		onNewWork<CallerEnvironment::EMPER>(emper::FiberHint{emper::FiberSource::local});
+		if constexpr (emper::STATS) {
+			uint64_t queueLength = pushed.size;
+			awss::stats.recordScheduledToLocalAndQueueLength(queueLength);
+		}
 	}
 	return pushed;
 }