1. Problem It Solves
A memory pool serves repeated allocations from a preallocated region, while benchmarking measures a focused operation and profiling locates where total time or memory goes. It makes an important constraint visible instead of leaving readers to guess. This lesson keeps only the C++11 core that fits one focused day.
2. Prerequisites
The ideas from Day 52, plus basic variables, functions, and output already introduced.
3. Core Idea
Mental model: A memory pool serves repeated allocations from a preallocated region, while benchmarking measures a focused operation and profiling locates where total time or memory goes. Identify the relevant value or state, who owns it, and whether the rule acts during compilation or execution.
4. Minimal Syntax
void* allocate(std::size_t n); auto start = std::chrono::steady_clock::now();5. How It Works
The example creates a tiny fixed state with no keyboard input.
C++11 or the standard-library contract applies today's rule.
The program prints the important result so it can be checked against the source.
6. Common Mistakes
A benchmark without warm-up, repeated samples, observable work, or a suitable clock can mainly measure noise or optimized-away code.
7. When to Use It
Use it when allocation frequency is measured as a real bottleneck and object lifetimes fit pool reset.
Avoid it when it hides ownership, lifetime, type, ordering, or cost.
8. Simple Example
A fixed aligned pool placement-constructs integers in batches, computes a checksum, and verifies that a steady-clock duration was captured. The .cpp keeps the data fixed and avoids unrelated abstraction.
Complete sample code
Source file
cpp11/53_memory_pool_custom_allocator_benchmark_profiling/main.cpp
#include <chrono>
#include <cstddef>
#include <iostream>
#include <new>
class IntPool {
public:
IntPool() : used_(0) {}
void* allocate() {
if (used_ == capacity) {
throw std::bad_alloc();
}
return storage_ + sizeof(int) * used_++;
}
void reset() { used_ = 0; }
private:
static const std::size_t capacity = 100;
alignas(int) unsigned char storage_[capacity * sizeof(int)];
std::size_t used_;
};
int main() {
IntPool pool;
volatile long long checksum = 0;
const auto start = std::chrono::steady_clock::now();
for (int batch = 0; batch < 10; ++batch) {
for (int i = 0; i < 100; ++i) {
int* value = new (pool.allocate()) int(batch * 100 + i);
checksum += *value;
}
pool.reset();
}
const auto end = std::chrono::steady_clock::now();
const auto elapsed = end - start;
std::cout << "checksum=" << checksum << '\n';
std::cout << "time_captured=" << (elapsed.count() >= 0) << '\n';
}
9. Key Takeaways
The feature is part of the C++11 scope used in this course.
Understand its lifetime, ownership, type, and ordering consequences.
Compile with warnings and prefer the smallest form that makes the rule obvious.
10. Self-Check Questions
Easy — How does a memory pool support repeated allocations? What different questions do benchmarking and profiling answer when deciding whether to use a pool?
Medium — Read the small example described above. What value or state should it print, and which rule produces that result?
Hard — Find and explain the subtle bug in this situation: A benchmark without warm-up, repeated samples, observable work, or a suitable clock can mainly measure noise or optimized-away code. What is the smallest C++11-safe correction?