我的控制器能够暂停，恢复和解决长期运行的承诺。 当我的控制器中止Promise时，我的控制器递归循环以某种方式被破坏。
几天前我了解了Promise，所以也许我对拒绝或捕获事情一无所知。
首先，可以在promise链的步骤之间检查一个状态变量。
var state = "idle"
可插入的垫片承诺来检查此状态变量
// insert this shim before each link of promise chain
function promise_to_check_pause_and_abort(x) {
if (state == "running") {
return Promise.resolve(x) // just keep going
} else if (state == "pause") {
let P = new Promise((resolve, reject) => {
let resume_cb = () => { resolve() }
pause_cb_queue.push(resume_cb)
});
return P;
} else if (state == "abort") {
return Promise.reject("aborted at stage " + x)
} else {
return promise.reject("should not be executing in this invalid state = " + state)
}
}
我真正的应用程序运行许多链式承诺，可能需要15分钟才能完成。这不是证明我的问题所必需的。所以这是一个简单的假任务，它会返回一个承诺。
function promise_to_do_something_long_running(n) {
if (isNaN(n)) {
n = 0;
}
if (n == 100) {
return Promise.resolve("done")
} else {
let P = new Promise((resolve, reject) => {
setTimeout(() => {
console.log("doing " + n);
resolve();
}, 100)
})
return P
.then(() => { return promise_to_check_pause_and_abort(n) })
.then(() => { return promise_to_do_something_long_running(n + 1) })
}
}
现在是一个简单的文本控制器，用于启动，暂停，恢复和中止上述长期运行的承诺。
// A recursive controller.
// Get response based on current running state.
// Regardless of response, do it again.
function controller() {
if (state == "running") {
rl.question("abort or pause :", (answer) => {
if (answer == "abort") {
state = "abort"
} else if (answer == "pause") {
state = "pause"
};
controller(); // regardless of response or state, get input again
})
} else if (state == "pause") {
rl.question("abort or resume :", (answer) => {
if (answer == "abort") {
state = "abort";
pause_cb_queue.forEach((cb) => { cb() })
pause_cb_queue = []
} else if (answer == "resume") {
state = "running"
pause_cb_queue.forEach((cb) => { cb() })
pause_cb_queue = []
};
controller(); // regardless of response or state, get input again
})
} else if (state == "idle") {
rl.question("start :", (answer) => {
if (answer == "start") {
state = "running";
// controller loop not dependent on resolution of this
// only state is
promise_to_do_something_long_running()
.then((a) => {
console.log("completed task, response :" + a);
state = "idle"
})
.catch((b) => {
console.log("task rejected with response :" + b);
state = "idle"
});
};
controller(); // regardless of response or state, get input again
})
}
}
controller();
一切都很完美，除非我中止，控制器递归中断并且不再向用户请求输入。如何执行
.catch((b) => {
console.log("task rejected with response :" + b);
state = "idle"
});
导致外部控制器递归停止？
在nodejs中运行的完整代码如下：
'use strict';
const readline = require('readline');
const rl = readline.createInterface({
input: process.stdin,
output: process.stdout
});
var state = "idle"
var pause_cb_queue = []
// insert this shim before each link of promise chain
function promise_to_check_pause_and_abort(x) {
if (state == "running") {
return Promise.resolve(x) // just keep going
} else if (state == "pause") {
let P = new Promise((resolve, reject) => {
let resume_cb = () => { resolve() }
pause_cb_queue.push(resume_cb)
});
return P;
} else if (state == "abort") {
return Promise.reject("aborted at stage " + x)
} else {
return promise.reject("should not be executing in this invalid state = " + state)
}
}
function promise_to_do_something_long_running(n) {
if (isNaN(n)) {
n = 0;
}
if (n == 100) {
return Promise.resolve("done")
} else {
let P = new Promise((resolve, reject) => {
setTimeout(() => {
console.log("doing " + n);
resolve();
}, 100)
})
return P
.then(() => { return promise_to_check_pause_and_abort(n) })
.then(() => { return promise_to_do_something_long_running(n + 1) })
}
}
// A recursive controller.
// Get response based on current running state.
// Regardless of response, do it again.
function controller() {
if (state == "running") {
rl.question("abort or pause :", (answer) => {
if (answer == "abort") {
state = "abort"
} else if (answer == "pause") {
state = "pause"
};
controller(); // regardless of response or state, get input again
})
} else if (state == "pause") {
rl.question("abort or resume :", (answer) => {
if (answer == "abort") {
state = "abort";
pause_cb_queue.forEach((cb) => { cb() })
pause_cb_queue = []
} else if (answer == "resume") {
state = "running"
pause_cb_queue.forEach((cb) => { cb() })
pause_cb_queue = []
};
controller(); // regardless of response or state, get input again
})
} else if (state == "idle") {
rl.question("start :", (answer) => {
if (answer == "start") {
state = "running";
// controller loop not dependent on resolution of this
// only state is
promise_to_do_something_long_running()
.then((a) => {
console.log("completed task, response :" + a);
state = "idle"
})
.catch((b) => {
console.log("task rejected with response :" + b);
state = "idle"
});
};
controller(); // regardless of response or state, get input again
})
}
}
controller();
答案 0 :(得分：1)
暂停和恢复承诺没有错。我的错误是缺少处理控制器中的中止状态。
} else if (state == "abort") {
rl.question("in abort state, no valid input :", (answer) => {
controller(); // regardless of response or state, get input again
})
通过上述补充，一切都很完美。我现在可以暂停承诺链。