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# Dev log
## **1. Process Management:**
The core architecture has been upgraded from a simple single queue to a Per-CPU scheduler, supporting multi-core concurrency.
* Process lifecycle: A complete process state machine has been implemented, including UNUSED, RUNNABLE, RUNNING, SLEEPING, and ZOMBIE states.
* Core operations:
* fork(): process cloning, supporting COW (copy-on-write) isolation of memory space between parent and child processes.
* exit(): process termination and resource cleanup.
* wait(): parent process waits for child process to exit.
* sleep()/wakeup(): channel-based sleep and wakeup mechanism.
* Scheduling algorithm:
* O(1) priority scheduling has been implemented (supporting 4 priority queues).
* Per-CPU RunQueue: each CPU has its own independent run queue.
* Supports Work Stealing: idle CPUs can fetch tasks from other CPUs’ queues.
## **2. Memory Management:**
A complete virtual and physical memory management system has been implemented.
* Physical Memory (PMM): Implements the Buddy System, supporting memory allocation and deallocation in $2^n$ pages.
* Virtual Memory (VM): Based on RISC-V Sv39 paging mode. Provides secure data copying from user space to kernel space (copyin).
* COW (Copy-On-Write): During fork, only page table entries are copied and pages are set to read-only; writes trigger page faults for physical copy, greatly improving process creation efficiency.
* Kernel heap: Implements a Slab Allocator, providing efficient allocation of small objects (such as struct Proc).
## **3. Synchronization:**
* Spinlock: Used to protect very short critical sections (e.g., scheduler lock, PMM lock), supports disabling interrupts to prevent deadlocks.
* Mutex (sleeping lock): Used for long critical sections (e.g., file I/O), allowing sleep while holding the lock.
* Lock Handoff: Implements a complex lock handoff mechanism in the scheduler to ensure atomicity of context switches.
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