hook.md

title	date	author
Hook总览	2025-01-20 02:00:00 -0800	loongs-zhang

Hook总览

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为什么hook?

在Coroutine::resume_with之后，一个协程可能会长时间占用调度线程(例如，陷入重度计算或系统调用)，从而拖慢被该线程调度的其他协程。为了解决陷入系统调用的问题，我们引入hook机制，这样当协程进入系统调用时，它会被自动挂起，从而让其他协程执行。

这带来了一个新问题，preemptive特性会发送大量信号，而信号会中断正在执行的系统调用。此外，由于大多数用户在代码中未处理信号，因此如果他们直接使用open-routine-core并且启用preemptive特性将导致灾难性后果。

什么是hook?

Hook可以通过在运行时插入自定义代码来修改或扩展现有代码的行为，甚至可以监控、拦截、修改和重定向系统调用。现在，让我们用一个例子来直观地体验它。

假设我们有以下测试代码：

use std::time::{Duration, Instant};

#[test]
fn test_hook() {
    let start = Instant::now();
    std::thread::sleep(Duration::MAX);
    let cost = Instant::now().duration_since(start);
    println!("cost: {:?}", cost);
}

如果我们不hook，因为std::thread::sleep(Duration::MAX)，这个测试几乎永远不会结束，但有了hook，我们可以在不更改测试代码的情况下将nanosleep系统调用重定向到我们的自定义代码，然后测试就会很快结束。

工作原理

sequenceDiagram
    Actor Your Project
    participant open-coroutine
    participant open-coroutine-hook
    participant open-coroutine-core
    
    Your Project ->> open-coroutine: depends on
    open-coroutine ->> open-coroutine-hook: depends on
    alt at compile time
        open-coroutine ->> open-coroutine: build open-coroutine-hook into dylib
        open-coroutine ->> open-coroutine: link open-coroutine-hook's dylib 
    else runtime
        Your Project -->> Operation System: logic execute syscall
        alt what actually happened
            Your Project ->> open-coroutine-hook: redirect syscall to open-coroutine-hook's syscall mod
            open-coroutine-hook ->> open-coroutine-core: call open-coroutine-core's syscall mod
            open-coroutine-core ->> Operation System: execute fast syscall actually
            Operation System ->> open-coroutine-core: return syscall result and errno
            open-coroutine-core -->> Operation System: maybe execute fast syscall many times
            open-coroutine-core -->> open-coroutine-core: maybe modify syscall result or errno
            open-coroutine-core ->> open-coroutine-hook: return syscall result and errno
            open-coroutine-hook ->> Your Project: return syscall result and errno
        end
        Operation System ->> Your Project: return syscall result and errno
    end

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