The Nachos API Javadoc can be found HERE. Alternatively, you can produce your own Javadoc by following the instruction in command line or through eclipse. This documentation is very important for you to understand the code structure of Nachos. Nachos 5.0j is composed of 7 main packages as summarized in Table 1.
| Packages |
|
| nachos.ag | Provides classes that can be used to automatically grade Nachos projects. |
| nachos.machine | Provides classes that implement the Nachos simulated machine. The key components of Nachos machine are implemented here. |
| nachos.network | Provides classes that allow Nachos processes to communicate over the network. |
| nachos.security | Provides classes that can be used to protect the host system from malicious Nachos kernels. |
| nachos.threads | Provides classes that support a multithreaded kernel. The logic of thread scheduling will be implemented here. |
| nachos.userprog | Provides classes that allow Nachos to load and execute single-threaded user programs in separate address spaces. |
| nachos.vm | Provides classes that allow Nachos processes to be demand paged, and to use a hardware TLB for address translation. |
Among these packages, nachos.machine is the most important one. The classes in this package implement the simulated machine, important abstract classes and data structures. The main entry point of the Nachos is also contained in this package, more specifically, in nachos.machine.Machine. Next, we will describe some important classes in nachos.machine. For a complete reference of the package, interested reader can check the Nachos Javadoc.
| Class Summary |
|
| ArrayFile | A read-only OpenFile backed by a byte array. |
| Coff | A COFF (common object file format) loader. This class combining with CoffSection define the internal structures of user program in Nachos. |
| CoffSection | A CoffSection manages a single section within a COFF executable. |
| Config | Provides routines to access the Nachos configuration. To understand how Nachos parse configure file, going through this class is a good idea. |
| Kernel | An OS kernel. This class is the superclass of nachos.threads.ThreadedKernel. |
| Lib | Provides miscellaneous library routines. |
| Machine | The master class of the simulated machine. It also contains the main entry of Nachos. |
| OpenFile | A file that supports reading, writing, and seeking. |
| StubFileSystem | This class implements a file system that redirects all requests to the host operating system’s file system. |
| TCB | A TCB simulates the low-level details necessary to create, context-switch, and destroy Nachos threads. |
| TranslationEntry | A single translation between a virtual page and a physical page. Note that TLB entries are of type TranslationEntry, the same class used for page table entries. |
Since nachos.machine implements the simulated Nachos machine, it should remain intact. Modification to Nachos is mostly limited to other packages. For example, the thread related projects will only involve changes to package nachos.threads.
According to the project requirement, you only need to focus on the specific packages. In the programming assignment, we will deal with nachos.threads, nachos.userprog, and nachos.vm. See Table 3– 5 for the classes in each package.
| Class Summary |
|
| Alarm | Uses the hardware timer to provide preemption, and to allow threads to sleep until a certain time. |
| Communicator | A communicator allows threads to synchronously exchange 32-bit messages. |
| Condition | An implementation of condition variables built upon semaphores. |
| Condition2 | An implementation of condition variables that disables interrupt()s for synchronization. |
| ElevatorController | A controller for all the elevators in an elevator bank. |
| KThread | A KThread is a thread that can be used to execute Nachos kernel code. |
| Lock | A Lock is a synchronization primitive that has two states, busy and free. |
| LotteryScheduler | A scheduler that chooses threads using a lottery. |
| PriorityScheduler | A scheduler that chooses threads based on their priorities. |
| Rider | A single rider. |
| RoundRobinScheduler | A round-robin scheduler tracks waiting threads in FIFO queues, implemented with linked lists. |
| Scheduler | Coordinates a group of thread queues of the same kind. |
| Semaphore | A Semaphore is a synchronization primitive with an unsigned value. |
| SynchList | A synchronized queue. |
| ThreadedKernel | A multi-threaded OS kernel. |
| ThreadQueue | Schedules access to some sort of resource with limited access constraints. |
| Class Summary |
|
| SynchConsole | Provides a simple, synchronized interface to the machine’s console. |
| UserKernel | A kernel that can support multiple user processes. |
| UserProcess | Encapsulates the state of a user process that is not contained in its user thread (or threads). |
| UThread | A UThread is KThread that can execute user program code inside a user process, in addition to Nachos kernel code. |
| Class Summary |
|
| VMKernel | A kernel that can support multiple demand-paging user processes. |