asynchronous - Emacs Lisp中async.el说 "Symbol'的函数定义无效的原因是什么？

Question

我使用异步在elisp中调用异步函数。

首先，我在github中测试自述代码，它运行良好。

然后我写一个测试代码:

(defun async-function ()
    (async-start
          ;; What to do in the child process
          (lambda ()
                (shell-command-to-string "~/test.sh"))

          ;; What to do when it finishes
          (lambda (result)
                     (message "Async process done, result is: %s" result)))

而test.sh代码非常简单:

#! /usr/bin/env sh
sleep 2
echo "shell finish"

它可以工作，但是当我像这样更改lisp代码时，它失败了:

;;;###autoload
(defun test ()
    (shell-command-to-string "~/test.sh"))

 (defun async-function ()
    (async-start
          ;; What to do in the child process
          (lambda ()
                (test))

          ;; What to do when it finishes
          (lambda (result)
                     (message "Async process done, result is: %s" result)))

结果是:

 error in process sentinel: Symbol's function definition is void: test

我使用 autoload函数加载函数文件，但结果告诉我找不到该文件。

我不知道会发生什么以及如何解决。

Answer 1

async.el的工作方式是产生另一个Emacs进程来评估表达式。在这种情况下，您可以在主Emacs进程中定义测试功能，但是异步Emacs进程无法从主进程访问函数和变量。如果要指定供异步调用使用的函数，请将它们放在文件中，然后将该文件加载到异步函数中。但是请记住，变量等不会转移。

这是一个示例，它在一个文件中:

;; ~/.emacs.d/my-functions.el
(defun test ()
  (sit-for 2)
  "Hello, World!.")

这是其他地方:

;; somewhere else
(async-start
 (lambda ()
   (load-file "~/.emacs.d/my-functions.el")
   (test))
 (lambda (result)
   (message "result: %s" result))) ;; will message hello world

关于共享变量，异步不支持此功能。您不能做的是启动一个异步函数，该函数会连续修改变量并希望可以在主emacs进程中访问它，甚至只是将变量传递给异步lambda，因为在打开该符号之前不会对其进行求值不存在的新流程。

我们可以利用Lisp的反引号语法将变量按值传递给异步函数。下面是在异步函数中使用局部变量和函数的一种非常怪诞的方法。

;; We will declare a local variable `myvar'
(setq myvar "Bob")

;; Here is a simple function, notice that it does not
;; refer to other non standard functions or other local variables
(defun hello (name)
  (format "Hello, %s!" name))


(defun my-async-function ()
  (async-start
   ;; notice the backquote!
   `(lambda ()
      ;; in our async lambda we dont use the local `myvar' variable,
      ;; instead we are replacing it with the current local value of `myvar'
      (set  'myvar ,myvar)
      ;; we can also do this by actually obtaining the lambda expression
      ;; behind `hello' and putting that inside our lambda
      (fset 'hello ,(symbol-function 'hello))
      ;; then we wait!
      (sit-for 1)
      ;; now we are modifiying the async copy of `myvar' 
      (setq myvar (concat myvar " Johnson"))
      ;; here we want the result of the async lambda to be a call to our
      ;; `hello' function, but we also want to update our local version
      ;; of myvar with its value in th async process, so we will return
      ;; a list of both values which we can handle in our callback
      (list myvar (hello myvar)))

   (lambda (result)
     ;; once we get the results we'll update our local version of `myvar'
     ;; with the value returned by the async function
     (setq myvar (first result))
     ;; then we can print out the message we recieved from the output
     ;; of our async `hello' call.
     (message "The new value myvar is: %s\nThe result of the function was: %s"
          myvar
          (second result)))))


;; executed top down, the async callback will message:

;;The new value myvar is: Bob Johnson
;;The result of the function was: Hello, Bob Johnson!

我已经抽象出了使用宏将值和变量替换为立即值的概念:value-bound-lambda，您可以获取宏并在此处查看示例:

value-bound-lambda example