为何CFTHREAD在循环中复用局部变量值？

在循环中创建CFTHREAD时，所有线程似乎都在使用最后一次循环的变量值，而非创建线程时的当前值。相关伪代码如下：

LOCAL.Items=[
    "ABC",
    "DEF",
    "GHI",
    "JKL",
    "MNO",
    "PQR",
    "STU",
    "VWX",
    "YZ"
];
for (LOCAL.item in LOCAL.Items) {
    writeoutput(LOCAL.item & "<br />");
}
for (LOCAL.item in LOCAL.Items) {
    thread name="items-#LOCAL.item#" action="run" {
        writelog(text=LOCAL.item, type="information", file="thread-test");
    }
}

第一个循环的输出符合预期：

ABC
DEF
GHI
JKL
MNO
PQR
STU
VWX
YZ

但thread-test.log中的日志显示大部分条目都是最后一个值"YZ"：

"Information","cfthread-23","03/11/24","13:18:40","MNO"
"Information","cfthread-28","03/11/24","13:18:40","YZ"
"Information","cfthread-23","03/11/24","13:18:40","YZ"
"Information","cfthread-28","03/11/24","13:18:40","YZ"
"Information","cfthread-23","03/11/24","13:18:40","YZ"
"Information","cfthread-28","03/11/24","13:18:40","YZ"
"Information","cfthread-23","03/11/24","13:18:40","YZ"
"Information","cfthread-28","03/11/24","13:18:40","YZ"
"Information","cfthread-23","03/11/24","13:18:40","YZ"

问题根源 #

这是因为CFTHREAD是异步执行的，线程内部引用的LOCAL.item是循环变量的引用，而非创建线程时的副本。当线程真正开始执行时，循环可能已经完成或者走到了后续迭代，此时LOCAL.item的值已经被更新为循环后期甚至最后一次的值。

解决方案 #

需要将当前迭代的LOCAL.item作为线程的属性参数传递进去，这样每个线程会获得独立的变量副本，不会受循环变量后续变化的影响。修改后的代码如下：

LOCAL.Items=[
    "ABC",
    "DEF",
    "GHI",
    "JKL",
    "MNO",
    "PQR",
    "STU",
    "VWX",
    "YZ"
];
for (LOCAL.item in LOCAL.Items) {
    writeoutput(LOCAL.item & "<br />");
}
for (LOCAL.item in LOCAL.Items) {
    thread name="items-#LOCAL.item#" action="run" currentItem=LOCAL.item {
        writelog(text=attributes.currentItem, type="information", file="thread-test");
    }
}

关键修改点： #

• 在thread标签中添加currentItem=LOCAL.item，将当前迭代的值作为线程属性传递
• 线程内部通过attributes.currentItem访问该值，确保拿到的是创建线程时的当前值，而非循环变量的引用

内容的提问来源于stack exchange，提问作者Eric Belair