Add eraseAt and thread-safe getNextElement functions to CustomVector

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Co-authored-by: clauspruefer <17313789+clauspruefer@users.noreply.github.com>

Author: Copilot

doc/CustomVector.rst

@@ -14,6 +14,7 @@ Key Features
 3. **Contiguous addressing**: Next segment address = previous address + segment_size_bytes
 4. **No iterators**: Designed to be 100% compatible with shared memory (no types that rely on other memory regions)
 5. **Simple interface**: Provides essential vector operations only
+6. **Thread-safe operations**: ``getNextElement()`` is thread-safe for multi-process/multi-threaded access
 
 Required Functions
 ------------------
@@ -23,6 +24,8 @@ Required Functions
 3. ✅ **push_back** element
 4. ✅ **get element** at element index
 5. ✅ **get elements count**
+6. ✅ **eraseAt** (remove element at specific index)
+7. ✅ **getNextElement** (thread-safe: get first element and remove it)
 
 Usage Example
 -------------
@@ -278,6 +281,59 @@ segment_size()
 
 Returns the segment size in bytes.
 
+eraseAt()
+~~~~~~~~~
+
+.. code-block:: cpp
+
+    void eraseAt(size_t index)
+
+Removes element at specified index. Throws ``std::out_of_range`` if index is out of bounds.
+
+This operation shifts all elements after the removed element forward by one position. Time complexity is O(n) where n is the number of elements after the removed element.
+
+**Example:**
+
+.. code-block:: cpp
+
+    CustomVector<int> vec(sizeof(int), shmem, 4096);
+    vec.push_back(10);
+    vec.push_back(20);
+    vec.push_back(30);
+    
+    vec.eraseAt(1);  // Removes element at index 1 (value 20)
+    // Vector now contains: [10, 30]
+
+getNextElement()
+~~~~~~~~~~~~~~~~
+
+.. code-block:: cpp
+
+    T getNextElement()
+
+**Thread-safe** operation that returns the first element and removes it from the vector. Throws ``std::out_of_range`` if vector is empty.
+
+This function is thread-safe and can be called from multiple threads or processes. It uses a process-shared mutex to ensure atomic get-and-remove operation, making it suitable for producer-consumer patterns in shared memory.
+
+**Example:**
+
+.. code-block:: cpp
+
+    CustomVector<int> vec(sizeof(int), shmem, 4096);
+    vec.push_back(100);
+    vec.push_back(200);
+    
+    int first = vec.getNextElement();  // Returns 100, removes it
+    int second = vec.getNextElement(); // Returns 200, removes it
+    // Vector is now empty
+
+**Thread-Safety:**
+
+The ``getNextElement()`` function uses a pthread mutex with ``PTHREAD_PROCESS_SHARED`` attribute, making it safe for:
+
+- Multi-threaded access within a single process
+- Multi-process access when the CustomVector is in shared memory
+
 Testing
 -------
 

src/CustomVector.hpp

@@ -4,6 +4,8 @@
 #include <cstdlib>
 #include <stdexcept>
 #include <new>
+#include <pthread.h>
+#include <cstring>
 
 /**
  * Minimalistic vector implementation with custom memory management.
@@ -17,6 +19,7 @@
  * - The data memory uses contiguous segment-based addressing
  * - Does not own the memory (no malloc/free)
  * - Template parameter T should be trivially copyable for optimal shared memory usage
+ * - Thread-safe getNextElement() operation using pthread mutex
  * 
  * Usage:
  *   void* shmem = mmap(NULL, 640000, PROT_READ | PROT_WRITE, 
@@ -33,6 +36,7 @@ class CustomVector {
     size_t size_;                // Current number of elements
     char* memory_base_;          // Base address of shared memory
     size_t memory_total_bytes_;  // Total size of shared memory region
+    pthread_mutex_t mutex_;      // Mutex for thread-safe operations
 
 public:
     /**
@@ -56,6 +60,13 @@ class CustomVector {
         if (shared_memory_size == 0) {
             throw std::invalid_argument("Shared memory size must be greater than 0");
         }
+        
+        // Initialize mutex with process-shared attribute for cross-process synchronization
+        pthread_mutexattr_t attr;
+        pthread_mutexattr_init(&attr);
+        pthread_mutexattr_setpshared(&attr, PTHREAD_PROCESS_SHARED);
+        pthread_mutex_init(&mutex_, &attr);
+        pthread_mutexattr_destroy(&attr);
     }
 
     /**
@@ -67,6 +78,8 @@ class CustomVector {
         for (size_t i = 0; i < size_; ++i) {
             get_element_ptr(i)->~T();
         }
+        // Destroy the mutex
+        pthread_mutex_destroy(&mutex_);
         // Note: We do NOT free memory_base_ as it's externally managed (e.g., via munmap)
     }
 
@@ -164,6 +177,68 @@ class CustomVector {
         return segment_size_bytes_;
     }
 
+    /**
+     * Removes element at specified index
+     * @param index Index of the element to remove
+     * @throws std::out_of_range if index is out of bounds
+     * 
+     * This operation shifts all elements after the removed element forward by one position.
+     * Time complexity: O(n) where n is the number of elements after the removed element.
+     */
+    void eraseAt(size_t index) {
+        if (index >= size_) {
+            throw std::out_of_range("Index out of bounds");
+        }
+
+        // Destroy the element at the index
+        get_element_ptr(index)->~T();
+
+        // Shift all elements after the erased element forward
+        for (size_t i = index; i < size_ - 1; ++i) {
+            T* current = get_element_ptr(i);
+            T* next = get_element_ptr(i + 1);
+            
+            // Use placement new to copy-construct in place
+            new (current) T(*next);
+            
+            // Destroy the old element
+            next->~T();
+        }
+
+        --size_;
+    }
+
+    /**
+     * Thread-safe operation: returns the first element and removes it from the vector
+     * @return Copy of the first element
+     * @throws std::out_of_range if vector is empty
+     * 
+     * This function is thread-safe and can be called from multiple threads or processes.
+     * It uses a mutex to ensure atomic get-and-remove operation.
+     */
+    T getNextElement() {
+        pthread_mutex_lock(&mutex_);
+        
+        try {
+            if (size_ == 0) {
+                pthread_mutex_unlock(&mutex_);
+                throw std::out_of_range("Cannot get next element: vector is empty");
+            }
+
+            // Get a copy of the first element
+            T result = *get_element_ptr(0);
+
+            // Remove the first element
+            eraseAt(0);
+
+            pthread_mutex_unlock(&mutex_);
+            return result;
+        } catch (...) {
+            pthread_mutex_unlock(&mutex_);
+            throw;
+        }
+    }
+
 private:
     /**
      * Gets pointer to element at specified index

test/integration/custom-vector/test-CustomVector.cpp

@@ -6,6 +6,7 @@
 #include <iostream>
 #include <sys/mman.h>
 #include <cstring>
+#include <vector>
 
 using namespace std;
 
@@ -345,3 +346,169 @@ BOOST_AUTO_TEST_CASE(test_custom_vector_placement_new_in_shared_memory) {
 
     munmap(shmpointer, 640000);
 }
+
+BOOST_AUTO_TEST_CASE(test_custom_vector_eraseAt) {
+    cout << "Test CustomVector eraseAt function" << endl;
+    
+    void* shmem = allocate_shared_memory(4096);
+    CustomVector<int> vec(sizeof(int), shmem, 4096);
+    
+    // Add some elements
+    vec.push_back(10);
+    vec.push_back(20);
+    vec.push_back(30);
+    vec.push_back(40);
+    vec.push_back(50);
+    
+    BOOST_CHECK_EQUAL(vec.size(), 5);
+    cout << "Added 5 elements: 10, 20, 30, 40, 50" << endl;
+    
+    // Test: Erase element at index 2 (value 30)
+    vec.eraseAt(2);
+    BOOST_CHECK_EQUAL(vec.size(), 4);
+    BOOST_CHECK_EQUAL(vec.at(0), 10);
+    BOOST_CHECK_EQUAL(vec.at(1), 20);
+    BOOST_CHECK_EQUAL(vec.at(2), 40);  // 40 should have shifted forward
+    BOOST_CHECK_EQUAL(vec.at(3), 50);
+    cout << "After erasing index 2: [10, 20, 40, 50]" << endl;
+    
+    // Test: Erase first element
+    vec.eraseAt(0);
+    BOOST_CHECK_EQUAL(vec.size(), 3);
+    BOOST_CHECK_EQUAL(vec.at(0), 20);
+    BOOST_CHECK_EQUAL(vec.at(1), 40);
+    BOOST_CHECK_EQUAL(vec.at(2), 50);
+    cout << "After erasing index 0: [20, 40, 50]" << endl;
+    
+    // Test: Erase last element
+    vec.eraseAt(2);
+    BOOST_CHECK_EQUAL(vec.size(), 2);
+    BOOST_CHECK_EQUAL(vec.at(0), 20);
+    BOOST_CHECK_EQUAL(vec.at(1), 40);
+    cout << "After erasing index 2: [20, 40]" << endl;
+    
+    // Test: Erase out of bounds should throw
+    BOOST_CHECK_THROW(vec.eraseAt(5), std::out_of_range);
+    cout << "Correctly threw exception for out of bounds erase" << endl;
+    
+    free_shared_memory(shmem, 4096);
+}
+
+BOOST_AUTO_TEST_CASE(test_custom_vector_getNextElement) {
+    cout << "Test CustomVector getNextElement function" << endl;
+    
+    void* shmem = allocate_shared_memory(4096);
+    CustomVector<int> vec(sizeof(int), shmem, 4096);
+    
+    // Add some elements
+    vec.push_back(100);
+    vec.push_back(200);
+    vec.push_back(300);
+    
+    BOOST_CHECK_EQUAL(vec.size(), 3);
+    cout << "Added 3 elements: 100, 200, 300" << endl;
+    
+    // Test: Get first element (should return 100 and remove it)
+    int first = vec.getNextElement();
+    BOOST_CHECK_EQUAL(first, 100);
+    BOOST_CHECK_EQUAL(vec.size(), 2);
+    BOOST_CHECK_EQUAL(vec.at(0), 200);
+    BOOST_CHECK_EQUAL(vec.at(1), 300);
+    cout << "Got next element: 100, remaining: [200, 300]" << endl;
+    
+    // Test: Get second element (should return 200 and remove it)
+    int second = vec.getNextElement();
+    BOOST_CHECK_EQUAL(second, 200);
+    BOOST_CHECK_EQUAL(vec.size(), 1);
+    BOOST_CHECK_EQUAL(vec.at(0), 300);
+    cout << "Got next element: 200, remaining: [300]" << endl;
+    
+    // Test: Get third element (should return 300 and remove it)
+    int third = vec.getNextElement();
+    BOOST_CHECK_EQUAL(third, 300);
+    BOOST_CHECK_EQUAL(vec.size(), 0);
+    cout << "Got next element: 300, remaining: []" << endl;
+    
+    // Test: Get from empty vector should throw
+    BOOST_CHECK_THROW(vec.getNextElement(), std::out_of_range);
+    cout << "Correctly threw exception for empty vector" << endl;
+    
+    free_shared_memory(shmem, 4096);
+}
+
+BOOST_AUTO_TEST_CASE(test_custom_vector_getNextElement_with_struct) {
+    cout << "Test CustomVector getNextElement with struct type" << endl;
+    
+    struct Payload_t {
+        char Payload[128];
+        uint16_t PayloadLength;
+    };
+    
+    void* shmem = allocate_shared_memory(4096);
+    CustomVector<Payload_t> vec(sizeof(Payload_t), shmem, 4096);
+    
+    // Add some struct elements
+    Payload_t p1;
+    strcpy(p1.Payload, "First payload");
+    p1.PayloadLength = 13;
+    vec.push_back(p1);
+    
+    Payload_t p2;
+    strcpy(p2.Payload, "Second payload");
+    p2.PayloadLength = 14;
+    vec.push_back(p2);
+    
+    BOOST_CHECK_EQUAL(vec.size(), 2);
+    cout << "Added 2 struct elements" << endl;
+    
+    // Test: Get first struct element
+    Payload_t first = vec.getNextElement();
+    BOOST_CHECK_EQUAL(std::string(first.Payload), "First payload");
+    BOOST_CHECK_EQUAL(first.PayloadLength, 13);
+    BOOST_CHECK_EQUAL(vec.size(), 1);
+    cout << "Got next element: '" << first.Payload << "' (length: " << first.PayloadLength << ")" << endl;
+    
+    // Test: Get second struct element
+    Payload_t second = vec.getNextElement();
+    BOOST_CHECK_EQUAL(std::string(second.Payload), "Second payload");
+    BOOST_CHECK_EQUAL(second.PayloadLength, 14);
+    BOOST_CHECK_EQUAL(vec.size(), 0);
+    cout << "Got next element: '" << second.Payload << "' (length: " << second.PayloadLength << ")" << endl;
+    
+    free_shared_memory(shmem, 4096);
+}
+
+BOOST_AUTO_TEST_CASE(test_custom_vector_thread_safety) {
+    cout << "Test CustomVector getNextElement thread safety" << endl;
+    
+    void* shmem = allocate_shared_memory(8192);
+    CustomVector<int> vec(sizeof(int), shmem, 8192);
+    
+    // Add many elements
+    const int NUM_ELEMENTS = 100;
+    for (int i = 0; i < NUM_ELEMENTS; ++i) {
+        vec.push_back(i);
+    }
+    
+    BOOST_CHECK_EQUAL(vec.size(), NUM_ELEMENTS);
+    cout << "Added " << NUM_ELEMENTS << " elements" << endl;
+    
+    // Test: Sequential getNextElement should work correctly
+    std::vector<int> retrieved;
+    for (int i = 0; i < NUM_ELEMENTS; ++i) {
+        int val = vec.getNextElement();
+        retrieved.push_back(val);
+    }
+    
+    BOOST_CHECK_EQUAL(vec.size(), 0);
+    BOOST_CHECK_EQUAL(retrieved.size(), NUM_ELEMENTS);
+    
+    // Verify all elements were retrieved in order
+    for (int i = 0; i < NUM_ELEMENTS; ++i) {
+        BOOST_CHECK_EQUAL(retrieved[i], i);
+    }
+    cout << "Successfully retrieved all " << NUM_ELEMENTS << " elements in order" << endl;
+    
+    free_shared_memory(shmem, 8192);
+}
+