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我在一个库中遇到了与此类似的东西，它似乎导致 Rust 在我的程序结束时出现恐慌。我删除了大部分不相关的代码，这似乎是重现它所需的最小示例。

这段代码似乎非常接近记录的使用std::thread_localand with。这里是否发生了某种reqwest::blocking::Client无法正确支持的破坏？还是在退出之前我应该​​做一些清理工作？

use reqwest::blocking::Client;

std::thread_local!(static CLIENT: Client = Client::new());

fn main() {
    match CLIENT.with(|c| {c.get("https://www.rust-lang.org").send()}) {
        Ok(_) => {
            println!("success!");
        },
        Err(_) => {
            println!("error!");
        }
    }
}

这是我得到的错误：

$ cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.15s
     Running `target\debug\example.exe`
success!
thread '<unnamed>' panicked at 'called `Option::unwrap()` on a `None` value', C:\Users\rober\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib/rustlib/src/rust\library\std\src\thread\mod.rs:1245:48
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

如果我避免使用thread_local并只初始化一个常规局部变量，它可以正常工作：

use reqwest::blocking::Client;

fn main() {
    let client: Client = Client::new();
    match client.get("https://www.rust-lang.org").send() {
        Ok(_) => {
            println!("success!");
        },
        Err(_) => {
            println!("error!");
        }
    }
}

我在 Windows 10 上运行rustc 1.49.0 (e1884a8e3 2020-12-29)

我的cargo.toml有reqwest = { version = "0.10", features = ["blocking"] }

如果我使用完整的回溯运行，我会得到以下输出

$ cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.16s
     Running `target\debug\example.exe`
success!
thread '<unnamed>' panicked at 'called `Option::unwrap()` on a `None` value', C:\Users\rober\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib/rustlib/src/rust\library\std\src\thread\mod.rs:1245:48
stack backtrace:
   0:     0x7ff6f376f54e - std::backtrace_rs::backtrace::dbghelp::trace
                               at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca\/library\std\src\..\..\backtrace\src\backtrace\dbghelp.rs:108
   1:     0x7ff6f376f54e - std::backtrace_rs::backtrace::trace_unsynchronized
                               at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca\/library\std\src\..\..\backtrace\src\backtrace\mod.rs:66
   2:     0x7ff6f376f54e - std::sys_common::backtrace::_print_fmt
                               at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca\/library\std\src\sys_common\backtrace.rs:67
   3:     0x7ff6f376f54e - std::sys_common::backtrace::_print::{{impl}}::fmt
                               at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca\/library\std\src\sys_common\backtrace.rs:46
   4:     0x7ff6f37844eb - core::fmt::write
                               at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca\/library\core\src\fmt\mod.rs:1078
   5:     0x7ff6f3768d58 - std::io::Write::write_fmt<std::sys::windows::stdio::Stderr>
                               at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca\/library\std\src\io\mod.rs:1518
   6:     0x7ff6f37720dd - std::sys_common::backtrace::_print
                               at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca\/library\std\src\sys_common\backtrace.rs:49
   7:     0x7ff6f37720dd - std::sys_common::backtrace::print
                               at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca\/library\std\src\sys_common\backtrace.rs:36
   8:     0x7ff6f37720dd - std::panicking::default_hook::{{closure}}
                               at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca\/library\std\src\panicking.rs:208
   9:     0x7ff6f3771cb8 - std::panicking::default_hook
                               at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca\/library\std\src\panicking.rs:227
  10:     0x7ff6f3772a4f - std::panicking::rust_panic_with_hook
                               at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca\/library\std\src\panicking.rs:593
  11:     0x7ff6f3772523 - std::panicking::begin_panic_handler::{{closure}}
                               at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca\/library\std\src\panicking.rs:497
  12:     0x7ff6f376fe8f - std::sys_common::backtrace::__rust_end_short_backtrace<closure-0,!>
                               at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca\/library\std\src\sys_common\backtrace.rs:141
  13:     0x7ff6f37724a9 - std::panicking::begin_panic_handler
                               at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca\/library\std\src\panicking.rs:495
  14:     0x7ff6f3782a60 - core::panicking::panic_fmt
                               at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca\/library\core\src\panicking.rs:92
  15:     0x7ff6f37829ac - core::panicking::panic
                               at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca\/library\core\src\panicking.rs:50
  16:     0x7ff6f363a940 - core::option::Option<core::result::Result<tuple<>, alloc::boxed::Box<Any, alloc::alloc::Global>>>::unwrap<core::result::Result<tuple<>, alloc::boxed::Box<Any, alloc::alloc::Global>>>
                               at C:\Users\rober\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\core\src\option.rs:386
  17:     0x7ff6f36169bb - std::thread::JoinInner<tuple<>>::join<tuple<>>
                               at C:\Users\rober\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\std\src\thread\mod.rs:1245
  18:     0x7ff6f36169fb - std::thread::JoinHandle<tuple<>>::join<tuple<>>
                               at C:\Users\rober\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\std\src\thread\mod.rs:1373
  19:     0x7ff6f32bfac1 - reqwest::blocking::client::{{impl}}::drop::{{closure}}
                               at C:\Users\rober\.cargo\registry\src\github.com-1ecc6299db9ec823\reqwest-0.10.10\src\blocking\client.rs:752
  20:     0x7ff6f32dcde9 - core::option::Option<std::thread::JoinHandle<tuple<>>>::map<std::thread::JoinHandle<tuple<>>,core::result::Result<tuple<>, alloc::boxed::Box<Any, alloc::alloc::Global>>,closure-1>
                               at C:\Users\rober\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\core\src\option.rs:453
  21:     0x7ff6f32bf8e1 - reqwest::blocking::client::{{impl}}::drop
                               at C:\Users\rober\.cargo\registry\src\github.com-1ecc6299db9ec823\reqwest-0.10.10\src\blocking\client.rs:752
  22:     0x7ff6f32d723f - core::ptr::drop_in_place<reqwest::blocking::client::InnerClientHandle>
                               at C:\Users\rober\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\core\src\ptr\mod.rs:175
  23:     0x7ff6f32e4832 - alloc::sync::Arc<reqwest::blocking::client::InnerClientHandle>::drop_slow<reqwest::blocking::client::InnerClientHandle>
                               at C:\Users\rober\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\alloc\src\sync.rs:951
  24:     0x7ff6f32e84a0 - alloc::sync::{{impl}}::drop<reqwest::blocking::client::InnerClientHandle>
                               at C:\Users\rober\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\alloc\src\sync.rs:1471
  25:     0x7ff6f32cee8e - core::ptr::drop_in_place<alloc::sync::Arc<reqwest::blocking::client::InnerClientHandle>>
                               at C:\Users\rober\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\core\src\ptr\mod.rs:175
  26:     0x7ff6f32cb1f5 - core::ptr::drop_in_place<reqwest::blocking::client::ClientHandle>
                               at C:\Users\rober\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\core\src\ptr\mod.rs:175
  27:     0x7ff6f32d6afe - core::ptr::drop_in_place<reqwest::blocking::client::Client>
                               at C:\Users\rober\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\core\src\ptr\mod.rs:175
  28:     0x7ff6f32a22b2 - core::ptr::drop_in_place<core::option::Option<reqwest::blocking::client::Client>>
                               at C:\Users\rober\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\core\src\ptr\mod.rs:175
  29:     0x7ff6f32a1c09 - core::mem::drop<core::option::Option<reqwest::blocking::client::Client>>
                               at C:\Users\rober\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\core\src\mem\mod.rs:882
  30:     0x7ff6f32a2ae2 - std::thread::local::fast::destroy_value<reqwest::blocking::client::Client>
                               at C:\Users\rober\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib\rustlib\src\rust\library\std\src\thread\local.rs:519
  31:     0x7ff6f3770b4b - std::sys_common::thread_local_dtor::register_dtor_fallback::run_dtors
                               at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca\/library\std\src\sys_common\thread_local_dtor.rs:43
  32:     0x7ff6f3775e58 - std::sys::windows::thread_local_key::run_dtors
                               at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca\/library\std\src\sys\windows\thread_local_key.rs:245
  33:     0x7ff6f3775e58 - std::sys::windows::thread_local_key::on_tls_callback
                               at /rustc/e1884a8e3c3e813aada8254edfa120e85bf5ffca\/library\std\src\sys\windows\thread_local_key.rs:214
  34:     0x7ffa829a5021 - RtlActivateActivationContextUnsafeFast
  35:     0x7ffa829a5103 - RtlActivateActivationContextUnsafeFast
  36:     0x7ffa829eb1b0 - LdrShutdownProcess
  37:     0x7ffa829eafad - RtlExitUserProcess
  38:     0x7ffa8289cdda - ExitProcess
  39:     0x7ffa8019ae58 - o_free
  40:     0x7ffa8019870f - exit
  41:     0x7ff6f378aaf7 - __scrt_common_main_seh
                               at d:\agent\_work\4\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:295
  42:     0x7ffa82897c24 - BaseThreadInitThunk
  43:     0x7ffa829ed4d1 - RtlUserThreadStart

看起来它确实与某种析构函数有关，我reqwest::blocking::client::{{impl}}::drop在完整的堆栈跟踪中看到，但我对 Rust 的了解还不够，无法形成一个更完整的关于这里发生的事情的理论。

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