arrieta/pmr_example.cpp

## pmr_example.cpp
// Example Polymorphic Memory Resource (std::pmr) Monotonic Buffer Resource.
// J. Arrieta, Nabla Zero Labs
//
// * Pre-allocate two buffers, one with space for 2 chars and one with space for 256 chars.
// * Filled pre-allocated buffers with underscores to peek into them later and see where memory was touched.
// * Create two monotonic_buffer_resources, one for each buffer.
// * Notice that the main pool receives a pointer to the "backup" pool.
// * Create a vector of char that uses the main memory resource.
// * Push back on the vector all chars from 'a' to 'z'.
// * See how the first char was allocated using the first memory resource (pool).
// * Subsequent pushbacks relied on the back-up memory resource.
// * The vector contains the correct data.
// * If `backup` is smaller (try), the vector would have started allocating on the heap.

#include <memory_resource>
#include <memory>
#include <vector>
#include <algorithm>
#include <iostream>
#include <numeric>

int main() {
  auto buffer_size = 2;
  auto backup_size = 256;

  auto buffer = std::make_unique<char[]>(buffer_size);
  auto backup = std::make_unique<char[]>(backup_size);

  std::fill_n(buffer.get(), buffer_size, '_');
  std::fill_n(backup.get(), backup_size, '_');

  auto upst = std::pmr::monotonic_buffer_resource(backup.get(), backup_size);
  auto pool = std::pmr::monotonic_buffer_resource(buffer.get(), buffer_size, &upst);

  std::pmr::vector<char> v(&pool);

  for (auto c = 'a'; c <= 'z'; ++c) {
      v.push_back(c);
  }
  std::cout << "main buffer contents:\n";
  std::for_each_n(buffer.get(), buffer_size, [idx=0]  (auto x) mutable { std::cout << (idx++) << " " << x << "\n";});
  std::cout << "backup buffer contents:\n";
  std::for_each_n(backup.get(), backup_size, [idx=0]  (auto x) mutable { std::cout << (idx++) << " " << x << "\n";});
  std::cout << "vector contents:\n";
  std::for_each(v.begin(), v.end(), [idx=0]  (auto x) mutable { std::cout << (idx++) << " " << x << "\n";});
}
	// Example Polymorphic Memory Resource (std::pmr) Monotonic Buffer Resource.
	// J. Arrieta, Nabla Zero Labs
	//
	// * Pre-allocate two buffers, one with space for 2 chars and one with space for 256 chars.
	// * Filled pre-allocated buffers with underscores to peek into them later and see where memory was touched.
	// * Create two monotonic_buffer_resources, one for each buffer.
	// * Notice that the main pool receives a pointer to the "backup" pool.
	// * Create a vector of char that uses the main memory resource.
	// * Push back on the vector all chars from 'a' to 'z'.
	// * See how the first char was allocated using the first memory resource (pool).
	// * Subsequent pushbacks relied on the back-up memory resource.
	// * The vector contains the correct data.
	// * If `backup` is smaller (try), the vector would have started allocating on the heap.

	#include <memory_resource>
	#include <memory>
	#include <vector>
	#include <algorithm>
	#include <iostream>
	#include <numeric>

	int main() {
	auto buffer_size = 2;
	auto backup_size = 256;

	auto buffer = std::make_unique<char[]>(buffer_size);
	auto backup = std::make_unique<char[]>(backup_size);

	std::fill_n(buffer.get(), buffer_size, '_');
	std::fill_n(backup.get(), backup_size, '_');

	auto upst = std::pmr::monotonic_buffer_resource(backup.get(), backup_size);
	auto pool = std::pmr::monotonic_buffer_resource(buffer.get(), buffer_size, &upst);

	std::pmr::vector<char> v(&pool);

	for (auto c = 'a'; c <= 'z'; ++c) {
	v.push_back(c);
	}
	std::cout << "main buffer contents:\n";
	std::for_each_n(buffer.get(), buffer_size, [idx=0] (auto x) mutable { std::cout << (idx++) << " " << x << "\n";});
	std::cout << "backup buffer contents:\n";
	std::for_each_n(backup.get(), backup_size, [idx=0] (auto x) mutable { std::cout << (idx++) << " " << x << "\n";});
	std::cout << "vector contents:\n";
	std::for_each(v.begin(), v.end(), [idx=0] (auto x) mutable { std::cout << (idx++) << " " << x << "\n";});
	}