rust - CpuPool 的生命周期问题

Question

我正在使用 tokio 和 futures-cpupool 编写一个简单的 RPC 服务器。服务器持有一个 BTreeMap 盒装闭包，函数名称作为键。当前的实现非常简单:

pub struct SlackerServiceSync<T>
    where T: Send + Sync + 'static
{
    functions: Arc<BTreeMap<String, RpcFnSync<T>>>,
    pool: CpuPool,
}

impl<T> SlackerServiceSync<T>
    where T: Send + Sync + 'static
{
    pub fn new(functions: Arc<BTreeMap<String, RpcFnSync<T>>>,
               threads: usize)
               -> SlackerServiceSync<T> {
        let pool = CpuPool::new(threads);
        SlackerServiceSync { functions, pool }
    }
}

impl<T> Service for SlackerServiceSync<T>
    where T: Send + Sync + 'static
{
    type Request = SlackerPacket<T>;
    type Response = SlackerPacket<T>;
    type Error = io::Error;
    type Future = BoxFuture<Self::Response, Self::Error>;

    fn call(&self, req: Self::Request) -> Self::Future {
        match req {
            SlackerPacket::Request(sreq) => {
                debug!("getting request: {:?}", sreq.fname);
                if let Some(f) = self.functions.get(&sreq.fname) {
                    self.pool
                        .spawn_fn(move || -> FutureResult<T, Self::Error> {
                                      ok(f(&sreq.arguments))
                                  })
                        .and_then(move |result| {
                            debug!("getting results");
                            ok(SlackerPacket::Response(SlackerResponse {
                                                           version: sreq.version,
                                                           code: RESULT_CODE_SUCCESS,
                                                           content_type: sreq.content_type,
                                                           serial_id: sreq.serial_id,
                                                           result: result,
                                                       }))
                        })
                        .map_err(|_| io::Error::new(io::ErrorKind::Other, "Oneshot canceled"))
                        .boxed()
                } else {
                    let error = SlackerError {
                        version: sreq.version,
                        code: RESULT_CODE_NOT_FOUND,
                        serial_id: sreq.serial_id,
                    };
                    ok(SlackerPacket::Error(error)).boxed()
                }
            }
            SlackerPacket::Ping(ref ping) => {
                ok(SlackerPacket::Pong(SlackerPong { version: ping.version })).boxed()
            }
            _ => err(io::Error::new(io::ErrorKind::InvalidInput, "Unsupported packet")).boxed(),
        }
    }
}

我目前被 self.functions.get(&sreq.fname) 上的这个生命周期问题阻止了。

error[E0495]: cannot infer an appropriate lifetime for lifetime parameter in function call due to conflicting requirements
   --> src/service.rs:103:49
    |
103 |                 if let Some(f) = self.functions.get(&sreq.fname) {
    |                                                 ^^^
    |
note: first, the lifetime cannot outlive the anonymous lifetime #1 defined on the body at 99:55...
   --> src/service.rs:99:56
    |
99  |       fn call(&self, req: Self::Request) -> Self::Future {
    |  ________________________________________________________^
100 | |         match req {
101 | |             SlackerPacket::Request(sreq) => {
102 | |                 debug!("getting request: {:?}", sreq.fname);
...   |
133 | |         }
134 | |     }
    | |_____^
note: ...so that reference does not outlive borrowed content
   --> src/service.rs:103:34
    |
103 |                 if let Some(f) = self.functions.get(&sreq.fname) {
    |                                  ^^^^^^^^^^^^^^
    = note: but, the lifetime must be valid for the static lifetime...
note: ...so that the type `[closure@src/service.rs:105:35: 107:36 f:&std::boxed::Box<for<'r> std::ops::Fn(&'r std::vec::Vec<T>) -> T + std::marker::Send + std::marker::Sync>, sreq:packets::SlackerRequest<T>]` will meet its required lifetime bounds
   --> src/service.rs:105:26
    |
105 |                         .spawn_fn(move || -> FutureResult<T, Self::Error> {
    |                          ^^^^^^^^

Similar code works without CpuPool .我无法完全理解编译器报告的错误。

Full code is here

Answer 1

事实证明，我需要通过像这样声明 RcpFnSync 将闭包包装到 Arc 中:

pub type RpcFnSync<T> = Arc<Fn(&Vec<T>) -> T + Send + Sync + 'static>;

然后在发送到另一个线程之前克隆它:

fn call(&self, req: Self::Request) -> Self::Future {
    match req {
        SlackerPacket::Request(sreq) => {
            debug!("getting request: {:?}", sreq.fname);
            if let Some(fi) = self.functions.get(&sreq.fname) {
                let f = fi.clone();

                self.pool
                    .spawn_fn(move || -> FutureResult<Self::Response, Self::Error> {
                        let result = f(&sreq.arguments);
                        ok(SlackerPacket::Response(SlackerResponse {
                                                       version: sreq.version,
                                                       code: RESULT_CODE_SUCCESS,
                                                       content_type: sreq.content_type,
                                                       serial_id: sreq.serial_id,
                                                       result: result,
                                                   }))
                    })
                    .boxed()
            } else {
                let error = SlackerError {
                    version: sreq.version,
                    code: RESULT_CODE_NOT_FOUND,
                    serial_id: sreq.serial_id,
                };
                ok(SlackerPacket::Error(error)).boxed()
            }
        }
        SlackerPacket::Ping(ref ping) => {
            ok(SlackerPacket::Pong(SlackerPong { version: ping.version })).boxed()
        }
        _ => err(io::Error::new(io::ErrorKind::InvalidInput, "Unsupported packet")).boxed(),
    }
}