Carve FixedSizeQueue out of MpscBoundedQueue

score/launch_manager/src/daemon/src/common/concurrency/BUILD

@@ -25,6 +25,29 @@ cc_library(
     ],
 )
 
+cc_library(
+    name = "fixed_size_queue",
+    hdrs = [
+        "fixed_size_queue.hpp",
+    ],
+    include_prefix = "score/mw/launch_manager/common/concurrency",
+    strip_include_prefix = "/score/launch_manager/src/daemon/src/common/concurrency",
+    visibility = ["//score:__subpackages__"],
+    deps = [
+        "@score_baselibs//score/language/futurecpp",
+    ],
+)
+
+cc_test(
+    name = "fixed_size_queue_test",
+    srcs = ["fixed_size_queue_test.cpp"],
+    visibility = ["//tests:__subpackages__"],
+    deps = [
+        ":fixed_size_queue",
+        "@googletest//:gtest_main",
+    ],
+)
+
 cc_library(
     name = "mpmc_concurrent_queue",
     hdrs = [
@@ -68,6 +91,7 @@ cc_library(
     strip_include_prefix = "/score/launch_manager/src/daemon/src/common/concurrency",
     visibility = ["//score:__subpackages__"],
     deps = [
+        ":fixed_size_queue",
         "@score_baselibs//score/language/futurecpp",
     ],
 )

score/launch_manager/src/daemon/src/common/concurrency/fixed_size_queue.hpp

@@ -0,0 +1,117 @@
+/********************************************************************************
+ * Copyright (c) 2026 Contributors to the Eclipse Foundation
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Apache License Version 2.0 which is available at
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ ********************************************************************************/
+
+#ifndef FIXED_SIZED_QUEUE_HPP_INCLUDE
+#define FIXED_SIZED_QUEUE_HPP_INCLUDE
+
+#include <cstddef>
+#include <optional>
+#include <vector>
+
+#include <score/assert.hpp>
+
+namespace score::lcm::internal
+{
+
+/// @brief Fixed-size FIFO queue
+/// @details Uses std::optional to eliminate default construction of 
+///          type T elements at construction
+/// @tparam T The type of elements stored in the queue.
+///          Supports move-only and copy-only types.
+template <typename T>
+class FixedSizeQueue
+{
+  public:
+    /// @brief Constructs a FixedSizeQueue with zero capacity.
+    /// @details push will always return false
+    ///          tryPop will always return std::nullopt
+    FixedSizeQueue() : capacity_{0U}, slots_{} {}
+
+    /// @brief Constructs a FixedSizeQueue with a fixed runtime capacity.
+    /// @details If the specified size is 0, it is equivalent
+    ///          to a default constructed FixedSizeQueue. 
+    /// @param size The desired maximum number of elements.
+    explicit FixedSizeQueue(std::size_t size) : capacity_(size) {
+        slots_.resize(capacity_); 
+    }
+
+    /// @brief Inserts a new element directly at the tail of the queue.
+    /// @tparam Args Variadic template arguments forwarded to the constructor of T.
+    /// @param args The arguments used to construct the object of type T.
+    /// @return true if the element was successfully inserted; false if the queue is full (overflow protection).
+    template <typename... Args>
+    bool push(Args&&... args) {
+        if(full()) {
+            return false;
+        }
+
+        slots_[tail_].emplace(std::forward<Args>(args)...);
+        tail_ = (tail_ + 1U) % capacity_;
+        count_++;
+
+        return true;
+    }
+
+
+    /// @brief Attempts to extract and remove the oldest element from the queue.
+    /// @details The popped element is immediately destroyed in the internal 
+    ///          buffer to free resources.
+    /// @return A std::optional containing the element, 
+    ///         or std::nullopt if the queue was empty (underflow protection).
+    std::optional<T> tryPop() {
+        if (empty())
+        {
+            return std::nullopt;
+        }
+
+        std::optional<T> item = std::move(slots_[head_]);
+        slots_[head_] = std::nullopt; 
+        head_ = (head_ + 1U) % capacity_;
+        count_--;
+
+        return item;
+    }
+
+    /// @brief Checks if the queue contains no elements.
+    /// @return true if empty, otherwise false.
+    bool empty() const { return (count_ == 0U); }
+
+    /// @brief Checks if the queue has reached its maximum capacity.
+    /// @return true if full, otherwise false.
+    bool full() const { return (count_ >= capacity_); }
+
+    /// @brief Retrieves the current number of active elements in the queue.
+    /// @return The count of stored elements.
+    std::size_t size() const { return count_;}; 
+
+    /// @brief Retrieves the capacity of the queue.
+    /// @return The capacity of the queue
+    std::size_t capacity() const { return capacity_;}; 
+
+
+  private:
+    /// @brief Index of the oldest element in the buffer (read index).
+    std::size_t head_ = 0U;
+    /// @brief Index where the next element will be inserted (write index).
+    std::size_t tail_ = 0U;
+    /// @brief Current number of active elements in the queue.
+    std::size_t count_ = 0U;
+    /// @brief Maximum capacity of the queue.
+    std::size_t capacity_;
+    /// @brief Internal buffer holding the optional elements.
+    std::vector<std::optional<T>> slots_;
+};
+
+}  // namespace score::lcm::internal
+
+#endif  // FIXED_SIZED_QUEUE_HPP_INCLUDE

score/launch_manager/src/daemon/src/common/concurrency/fixed_size_queue_test.cpp

@@ -0,0 +1,195 @@
+/********************************************************************************
+ * Copyright (c) 2026 Contributors to the Eclipse Foundation
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Apache License Version 2.0 which is available at
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ ********************************************************************************/
+
+#include "score/mw/launch_manager/common/concurrency/fixed_size_queue.hpp"
+
+#include <gtest/gtest.h>
+
+#include <optional>
+#include <type_traits>
+#include <vector>
+
+using namespace score::lcm::internal;
+
+TEST(FixedSizeQueue, StaticProperties) {
+
+    RecordProperty("Description", "Verify that all special member functions are defined");
+
+    bool is_dc = std::is_default_constructible_v<FixedSizeQueue<int>>;
+    ASSERT_TRUE(is_dc);
+    bool is_mc = std::is_move_constructible_v<FixedSizeQueue<int>>;
+    ASSERT_TRUE(is_mc);
+    bool is_cc = std::is_copy_constructible_v<FixedSizeQueue<int>>;
+    ASSERT_TRUE(is_cc);
+    bool is_ma = std::is_move_assignable_v<FixedSizeQueue<int>>;
+    ASSERT_TRUE(is_ma);
+    bool is_ca = std::is_copy_assignable_v<FixedSizeQueue<int>>;
+    ASSERT_TRUE(is_ca);
+    bool is_de = std::is_destructible_v<FixedSizeQueue<int>>;
+    ASSERT_TRUE(is_de);
+}
+
+TEST(FixedSizeQueue, ZeroCapacityAllMemberFunctionsReturns) {
+
+    // clang-format off
+    RecordProperty("Description", "Verify that on zero capacity "
+                                  "full() returns true "
+                                  "empty() returns true "
+                                  "size() returns 0 " 
+                                  "capacity() returns 0 "
+                                  "push returns false "
+                                  "tryPop() turns std::nullopt"); 
+    // clang-format on
+
+    FixedSizeQueue<int> queue_dc;
+    FixedSizeQueue<int> queue0{0};
+    FixedSizeQueue<int> zero_cap_queues[2] = {queue_dc, queue0};
+
+    for(FixedSizeQueue<int> & q : zero_cap_queues) {
+        EXPECT_TRUE(q.full());
+        EXPECT_TRUE(q.empty());
+        EXPECT_EQ(q.size(), 0U);
+        EXPECT_EQ(q.capacity(), 0U);
+        EXPECT_FALSE(q.push(1));
+        EXPECT_EQ(q.tryPop(), std::nullopt);
+    }
+}
+
+TEST(FixedSizeQueue, CapacityFunctions)  {
+
+    // clang-format off
+    RecordProperty("Description", "Verify that on capacity bigger zero the capacity functions"
+                                  "full() returns false "
+                                  "empty() returns true "
+                                  "size() returns 0 " 
+                                  "capacity() returns the capacity "
+                                  "initially"); 
+    // clang-format on
+
+    const std::size_t cap{5U};
+    FixedSizeQueue<int> queue_cap_bigger_zero{cap};
+    EXPECT_FALSE(queue_cap_bigger_zero.full());
+    EXPECT_TRUE(queue_cap_bigger_zero.empty());
+    EXPECT_EQ(queue_cap_bigger_zero.size(), 0U);
+    EXPECT_EQ(queue_cap_bigger_zero.capacity(), cap);
+}
+
+TEST(FixedSizeQueue, CapacityFunctionSizeRetrunsNumberOfElementsInTheQueue)  {
+
+    RecordProperty("Description", "Verify that the capacity function size retruns the number of elements in the queue."); 
+
+    const std::size_t cap{5U};
+    std::size_t no_elements{0U};
+    FixedSizeQueue<int> queue_cap_five{cap};
+
+    EXPECT_EQ(queue_cap_five.size(), no_elements);
+
+    while(!queue_cap_five.full()) {
+        EXPECT_TRUE(queue_cap_five.push(1));
+        ++no_elements;
+        RecordProperty("Description", "Verify that push increments the size by one."); 
+        EXPECT_EQ(queue_cap_five.size(), no_elements);
+    }
+
+    RecordProperty("Description", "Verify that the capacity function full() retruns true if the number of elements reach the capacity."); 
+    EXPECT_EQ(queue_cap_five.capacity(), no_elements);
+    EXPECT_EQ(cap, no_elements);
+}   
+
+TEST(FixedSizeQueue, ModifierFunctionsPushAndTryPopImplementAFIFO)  {
+
+    RecordProperty("Description", "Verify that modifier functions push and try pop implement a FIFO."); 
+
+    const std::size_t cap{5U};
+    FixedSizeQueue<int> queue_cap_five{cap};
+    auto elements = {11 ,22, 33, 44, 55};
+
+    for(auto & e : elements) {
+        EXPECT_TRUE(queue_cap_five.push(e));
+    }
+
+    EXPECT_EQ(queue_cap_five.size(), cap);
+    EXPECT_TRUE(queue_cap_five.full());
+
+    std::size_t no_elements{queue_cap_five.size()};
+
+    for(auto & e : elements) {
+        RecordProperty("Description", "Verify that tryPop returns heads value."); 
+        EXPECT_EQ(queue_cap_five.tryPop(), e);
+        --no_elements;
+        RecordProperty("Description", "Verify that tryPop decrements the size by one."); 
+        EXPECT_EQ(queue_cap_five.size(), no_elements);
+    }
+
+    RecordProperty("Description", "Verify that empty() retruns true if the queue is drained."); 
+    EXPECT_TRUE(queue_cap_five.empty());
+    RecordProperty("Description", "Verify that size() retruns zero if the queue is drained."); 
+    EXPECT_EQ(queue_cap_five.size(), 0U);
+}   
+
+TEST(FixedSizeQueue, ModifierFunctionPushReturnsFalseIfTheQueueIsFull) {
+
+    RecordProperty("Description", "Verify that modifier function push returns false if the queue is full."); 
+
+    const std::size_t cap{5U};
+    FixedSizeQueue<int> queue_cap_five{cap};
+    auto elements = {11, 22, 33, 44, 55};
+
+    for(auto & e : elements) {
+        EXPECT_TRUE(queue_cap_five.push(e));
+    }
+
+    EXPECT_TRUE(queue_cap_five.full());
+    EXPECT_FALSE(queue_cap_five.push(66));
+}
+
+TEST(FixedSizeQueue, TailAndHeadWrap) {
+
+    RecordProperty("Description", "Verify that tail and head wrap."); 
+
+    const std::size_t cap{3U};
+    FixedSizeQueue<int> queue_cap_three{cap};
+
+    auto elements = {1, 2, 3};
+    for(auto & e : elements) {
+        EXPECT_TRUE(queue_cap_three.push(e));
+    }
+
+    EXPECT_EQ(queue_cap_three.size(), queue_cap_three.capacity());
+    // {1, 2, 3}
+    // {H, 2, T}
+
+    EXPECT_EQ(queue_cap_three.tryPop(), 1);
+    EXPECT_EQ(queue_cap_three.size(), 2U);
+    // { , 2, 3}
+    // { , H, T}
+
+    EXPECT_TRUE(queue_cap_three.push(4));
+    EXPECT_EQ(queue_cap_three.size(), queue_cap_three.capacity());
+    // {4, 2, 3}
+    // {T, H, 3}
+
+    EXPECT_EQ(queue_cap_three.tryPop(), 2);
+    EXPECT_EQ(queue_cap_three.size(), 2U);
+    // {4,  , 3}
+    // {T,  , H}
+
+
+    EXPECT_EQ(queue_cap_three.tryPop(), 3);
+    EXPECT_EQ(queue_cap_three.size(), 1U);
+    // {4,   ,  }
+    // {TH,  ,  }
+
+    EXPECT_EQ(queue_cap_three.tryPop(), 4);
+    EXPECT_EQ(queue_cap_three.size(), 0U);
+}