Understanding the C++17 PMR Standard Allocators and Track All the Things

• 0:00 Introduction: Jason Turner, host of C++ Weekly, discusses the PMR memory resource and its various allocators.
• 0:17 Memory Resource: The memory resource is an abstract interface that provides a way to allocate and deallocate memory.
• 1:01 Implementing Memory Resources: Implementing a custom memory resource involves overriding the virtual functions do_allocate, do_deallocate, and do_is_equal.
• 1:20 Standard Library Memory Resources: The standard library provides several pre-built memory resources, including the monotonic_buffer_resource, synchronized_pool_resource, and unsynchronized_pool_resource.
• 1:42 Monotonic Buffer Resource: The monotonic_buffer_resource allocates memory in a contiguous block, with no deallocation (a no-op). It offers efficient performance by avoiding fragmentation and providing contiguous blocks of data.
• 4:02 Synchronized & Unsynchronized Pool Resources: The synchronized_pool_resource and unsynchronized_pool_resource provide thread-safe and thread-unsafe memory allocation respectively. They organize memory into pools of different block sizes, allowing for efficient allocation and deallocation.
• 5:56 Upstream Allocator: Both the pool_resource and monotonic_buffer_resource have an upstream allocator, which is used when the resource needs more memory. The pool_resource can be given a monotonic_buffer_resource as its upstream, allowing for the allocation of all data in a single contiguous block.
• 7:54 Deallocation with Pool Resources: The pool_resource performs actual deallocation, allowing for memory reuse. In contrast, the monotonic_buffer_resource does not deallocate memory.
• 8:45 Null Memory Resource: The null_memory_resource is a statically defined resource that throws a bad_alloc exception when attempting allocation and has no effect on deallocation.
• 8:53 New/Delete Resource: The new_delete_resource is the default upstream allocator for monotonic_buffer_resources, simply using new and delete for allocation and deallocation.
• 9:40 Get/Set Default Resource: The get_default_resource function retrieves the default resource, which is the new_delete_resource. The set_default_resource function can be used to set a custom default allocator.
• 11:26 Rogue PMR Allocation: The null memory resource can be used to track and log unexpected allocations, potentially causing errors.
• 13:45 Combining Resources: By combining memory resources such as the monotonic_buffer_resource and the pool_resource, developers can achieve benefits like contiguous memory for data structures and efficient memory management with deallocation.
• 17:44 Example & Takeaways: Jason provides an example of how to use these resources to track and log allocations, demonstrating the power and flexibility of the PMR system.
• 20:30 Conclusion: The PMR provides tools to track, log, and manage allocations, allowing for more controlled and efficient memory use in C++ applications.
• 20:57 Upcoming Episode: The next episode will discuss efficiency considerations related to PMR memory resources.