# Resource Quota

This directory contains the implementation of the gRPC resource quota system.

## Overarching Purpose

The resource quota system provides a mechanism for controlling the amount of resources (e.g., memory, threads) that are used by gRPC. This can be used to prevent gRPC from consuming too many resources and to ensure that the system remains stable.

## Core Concepts

*   **`ResourceQuota`**: The `ResourceQuota` class is the main class for managing resource quotas. It is a container for a `MemoryQuota` and a `ThreadQuota`.
*   **`MemoryQuota`**: The `MemoryQuota` class is responsible for managing memory usage. It provides a way to reserve and release memory, and it can be configured to limit the total amount of memory that can be used.
*   **`ThreadQuota`**: The `ThreadQuota` class is responsible for managing thread usage. It provides a way to reserve and release threads, and it can be configured to limit the total number of threads that can be used.
*   **`Arena`**: An `Arena` is a custom memory allocator that is used by the resource quota system. It is designed to be very fast, and it is used to allocate memory for things like call objects and metadata. In addition to memory allocation, the Arena also serves as an index for context objects associated with a call, indexed by type. This allows various parts of the gRPC stack to attach and retrieve objects within the scope of a single Arena.

## Files

*   **`resource_quota.h`, `resource_quota.cc`**: These files define the `ResourceQuota` class.
*   **`memory_quota.h`, `memory_quota.cc`**: These files define the `MemoryQuota` class.
*   **`thread_quota.h`, `thread_quota.cc`**: These files define the `ThreadQuota` class.
*   **`arena.h`, `arena.cc`**: These files define the `Arena` class.
*   **`api.h`, `api.cc`**: These files define the public C API for the resource quota system.

## Notes

*   The resource quota system is a key component of gRPC's reliability and stability story. It helps to prevent gRPC from consuming too many resources and to ensure that the system remains stable under heavy load.
*   The resource quota system is highly configurable. It can be configured to limit the amount of memory and threads that are used by gRPC, as well as the rate at which these resources are consumed.
*   The `Arena` is a particularly important component of the resource quota system. It is a highly optimized memory allocator that is designed to be very fast. It is used to allocate memory for all of the per-call data structures in gRPC, and it is a key reason why gRPC is so performant.
