Understanding Android: The Java Virtual Machine ART

This book is the volume in the "Understanding Android" series devoted to dissecting the ART virtual machine. In 14 chapters, it takes reading real source code as its main thread and systematically explains the architecture and implementation principles of ART, Android's runtime environment. The author first equips readers with the tools, environment, and reading methods needed to read source code, then unpacks three file formats in turn—Class files, dex files, and ELF files—which are the necessary foundation for understanding the Dalvik and ART virtual machines. Next comes the key C++11 knowledge needed to read ART source code. The middle section follows the creation and startup of ArtRuntime as its main thread, connecting ART's major modules, key classes and data structures, class parsing, loading, linking, and initialization, and compilation-related principles. It then goes deep into the core stages of virtual machine operation: the dex2oat process that converts dex bytecode to machine code and the .oat and .art file formats, interpretation and JIT, exception delivery and handling, and the implementation of JNI in the native environment. Finally it focuses on Java thread execution (thread suspension and resumption, synchronized, Object wait/notify, volatile reads and writes), memory allocation and release, garbage collector implementation, and Java Reference handling. The book uses non-standard UML diagrams to show class relationships and data structures, with theoretical explanation and source code excerpts corroborating each other. It is suitable for engineers who want to understand Android system and application runtime mechanisms from the ground up.