SBCL 中多线程的原子操作

Question

加载包含原子操作的函数时出现错误。举个简单的例子，文件 test.lisp 包含：

(defparameter *count* 0)
(defun test ()
  (sb-ext:atomic-incf *count*))

生成以下错误：

* (load "d:\test.lisp")

; file: d:/test.lisp
; in: DEFUN TEST
;     (ATOMIC-INCF *COUNT*)
;
; caught ERROR:
;   during macroexpansion of (ATOMIC-INCF *COUNT*). Use *BREAK-ON-SIGNALS* to
;   intercept.
;
;    Invalid first argument to ATOMIC-INCF: *COUNT*
;
; compilation unit finished
;   caught 1 ERROR condition
T
*

为什么*count*无效？

Answer 1

来自文档字符串：

PLACE must access one of the following:
 - a DEFSTRUCT slot with declared type (UNSIGNED-BYTE 64)
   or AREF of a (SIMPLE-ARRAY (UNSIGNED-BYTE 64) (*))
   The type SB-EXT:WORD can be used for these purposes.
 - CAR or CDR (respectively FIRST or REST) of a CONS.
 - a variable defined using DEFGLOBAL with a proclaimed type of FIXNUM.
Macroexpansion is performed on PLACE before expanding ATOMIC-INCF.

我怀疑这些是为了避免在进行比较和交换时进行运行时检查。

Answer 2

要回答上面关于如何将 atomic-incf 与声明的全局变量一起用作 fixnum 的问题，这对我有用：

(declaim (fixnum **var**))
(sb-ext:defglobal **var** 0)
(sb-ext:atomic-incf **var**)

Answer 3

(defparameter *count* (list 0))

(defun test ()
   (sb-ext:atomic-incf (car *count*)))

(test)

SBCL 中多线程的原子操作

Atomic Operations for Multithreading in SBCL

multithreading

sbcl

common-lisp