HAL interface definition language or HIDL (pronounced “hide-l”) is an interface description language (IDL) to specify the interface between a HAL and its users. It allows specifying types and method calls, collected into interfaces and packages. More broadly, HIDL is a system for communicating between codebases that may be compiled independently.
HIDL 是用于指定 HAL 与其用户之间接口的一个接口描述语言（Interface Description Language），它允许定义变量和函数类型做成封装接口给其他程序调用。通俗的说，HIDL是两个独立程序的桥梁，另外两个程序可以独自编译生成互不影响。
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HIDL is intended to be used for inter-process communication (IPC). Communication between processes is referred to as Binderized. For libraries that must be linked to a process, a passthough mode is also available (not supported in Java).
HIDL specifies data structures and method signatures, organized in interfaces (similar to a class) that are collected into packages. The syntax of HIDL will look familiar to C++ and Java programmers, though with a different set of keywords. HIDL also uses Java-style annotations.
The goal of HIDL is that the framework can be replaced without having to rebuild HALs. HALs will be built by vendors or SOC makers and put in a /vendor partition on the device, enabling the framework, in its own partition, to be replaced with an OTA without recompiling the HALs.
设计 HIDL 这个机制的目的，主要是想把**框架（framework）**与 HAL 进行隔离，使得框架部分可以直接被覆盖、更新，而不需要重新对 HAL 进行编译。HAL 的部分将会放在设备的 /vendor 分区中，并且是由设备供应商（vendors）或 SOC 制造商来构建。这使得框架部分可以通过 OTA 方式更新，同时不需要重新编译 HAL。
