From fc2fd18c368f1c11decfc2c15b9e18b3841e26fe Mon Sep 17 00:00:00 2001
From: WangRunji <wangrunji0408@163.com>
Date: Sat, 22 Sep 2018 17:29:20 +0800
Subject: [PATCH] Add docs for thread::spawn()
---
crate/process/src/thread.rs | 40 +++++++++++++++++++++++++++++++------
1 file changed, 34 insertions(+), 6 deletions(-)
diff --git a/crate/process/src/thread.rs b/crate/process/src/thread.rs
index 8786cc8..818a28a 100644
--- a/crate/process/src/thread.rs
+++ b/crate/process/src/thread.rs
@@ -73,34 +73,61 @@ impl<S: ThreadSupport> ThreadMod<S> {
}
/// Spawns a new thread, returning a JoinHandle for it.
+ ///
+ /// `F`: Type of the function `f`
+ /// `T`: Type of the return value of `f`
pub fn spawn<F, T>(f: F) -> JoinHandle<S, T>
where
F: Send + 'static + FnOnce() -> T,
T: Send + 'static,
{
info!("spawn:");
+
+ // 注意到下面的问题：
+ // Processor只能从入口地址entry+参数arg创建新线程
+ // 而我们现在需要让它执行一个未知类型的（闭包）函数f
+
+ // 首先把函数本体（代码数据）置于堆空间中
let f = Box::into_raw(Box::new(f));
- let pid = S::processor().add(Context::new_kernel(kernel_thread_entry::<S, F, T>, f as usize));
- return JoinHandle {
- thread: Thread { pid, mark: PhantomData },
- mark: PhantomData,
- };
+ // 定义一个静态函数作为新线程的入口点
+ // 其参数是函数f在堆上的指针
+ // 这样我们就把函数f传到了一个静态函数内部
+ //
+ // 注意到它具有泛型参数，因此对每一次spawn调用，
+ // 由于F类型是独特的，因此都会生成一个新的kernel_thread_entry
extern fn kernel_thread_entry<S, F, T>(f: usize) -> !
where
S: ThreadSupport,
F: Send + 'static + FnOnce() -> T,
T: Send + 'static,
{
+ // 在静态函数内部：
+ // 根据传进来的指针，恢复f
let f = unsafe { Box::from_raw(f as *mut F) };
+ // 调用f，并将其返回值也放在堆上
let ret = Box::new(f());
-// unsafe { LocalKey::<usize>::get_map() }.clear();
+ // 清理本地线程存储
+ // unsafe { LocalKey::<usize>::get_map() }.clear();
+ // 让Processor退出当前线程
+ // 把f返回值在堆上的指针，以线程返回码的形式传递出去
let mut processor = S::processor();
let pid = processor.current_pid();
processor.exit(pid, Box::into_raw(ret) as usize);
processor.schedule();
+ // 再也不会被调度回来了
unreachable!()
}
+
+ // 在Processor中创建新的线程
+ let pid = S::processor().add(Context::new_kernel(kernel_thread_entry::<S, F, T>, f as usize));
+
+ // 接下来看看`JoinHandle::join()`的实现
+ // 了解是如何获取f返回值的
+ return JoinHandle {
+ thread: Thread { pid, mark: PhantomData },
+ mark: PhantomData,
+ };
}
/// Cooperatively gives up a timeslice to the OS scheduler.
@@ -155,6 +182,7 @@ impl<S: ThreadSupport, T> JoinHandle<S, T> {
let mut processor = S::processor();
match processor.current_wait_for(self.thread.pid) {
WaitResult::Ok(_, exit_code) => unsafe {
+ // Find return value on the heap from the exit code.
Ok(*Box::from_raw(exit_code as *mut T))
}
WaitResult::NotExist => Err(()),