[英]setTimeout function triggers callback twice
我有一个写入 function,它基本上将数据添加到队列并每 500 毫秒发送一次数据,我使用了几个 setTimeouts 来写入数据,如下所示。 并且分析日志我怀疑 setTimeout 被调用了两次,我想知道这是否可能? 可能的解决方法是什么?
import BleManager from 'react-native-ble-manager';
const BleManagerModule = NativeModules.BleManager;
const bleManagerEmitter = new NativeEventEmitter(BleManagerModule);
class bleHandler {
constructor() {
this.writeQueue = [];
bleManagerEmitter.addListener('BleManagerDidUpdateValueForCharacteristic', this.handleUpdateValueForCharacteristic);
}
//this function will be called when ble receives data from peripheral.
handleUpdateValueForCharacteristic(data){
// do something with data
//send ack that data is received.
this.writeData("AB:CD:EF:GH:IJ", " Some Important Message text ");
}
writeData(peripheralID, data) {
console.log("Adding data to Queue " + data);
if (this.writeQueue.length == 0) {
this.writeQueue.push(data);
setTimeout(() => this.sendData(peripheralID, data), 500);
} else
this.writeQueue.push(data);
console.log("New Queue Length = " + this.writeQueue.length);
}
sendData = (peripheralID, data) => {
if (data.length > 0 && peripheralID && this.writeQueue.length > 0) {
var byteBuf = this.formatData(data);
console.log("============" + slicedData + " and length = " + slicedData.length + " at Date = " + new Date().valueOf());
console.log("Writing Message : " + byteBuf );
this.handleWriteWithoutResponse(peripheralID, UUID, CHAR, byteBuf).then(() => {
console.log("success writing data ");
data = data.substring(PACKET_SIZE - 5);
if (data.length > 0) {
setTimeout(() => {
this.writeQueue[0] = data;
this.sendData(peripheralID, data)
}, 500);
} else {
this.writeQueue.shift();
setTimeout(() => {
if (this.writeQueue.length > 0)
this.sendData(peripheralID, this.writeQueue[0]);
}, 500);
}
}).catch((error) => {
console.log("error writing data ", error);
});
}
}
}
const bleModule = new bleHandler();
export default bleModule;
日志
11:13:28 log Adding data to Queue " Some Important Message text "
11:13:28 log New Queue Length = 1
11:13:28 log ============" Some Important Message text " and length = 28 at Date = 1597680808275
11:13:28 log Writing Message : 9876543211223A2243222C202233223A7B2241636B223A223230302212345
11:13:28 log ============" Some Important Message text " and length = 28 at Date = 1597680808276
11:13:28 log Writing Message : 9876543211223A2243222C202233223A7B2241636B223A223230302212345
11:13:28 log success writing data
11:13:28 log success writing data
现在,如果您检查 IOS 中的日志,我看到发送数据在 (1597680808276 - 1597680808275) 1 ms 间隔内被调用两次,它是从 setTimeout function 调用的。js 中的 setTimeout 有问题吗? 或者可能是 react-native 问题或 safari 问题? 我该如何解决这个问题。 几年前,我在 nodejs 中看到过类似的问题。
注意:我使用 react-native-ble-manager 发送/接收数据。
问题的根本原因是 function sendData
调用自身。
sendData = (peripheralID, data) => {
if (data.length > 0 && peripheralID && this.writeQueue.length > 0) {
// ...
if (data.length > 0) {
setTimeout(() => {
// ...
this.sendData(peripheralID, data) ---> Recursive call
}, 500);
} else {
// ...
setTimeout(() => {
if (this.writeQueue.length > 0)
this.sendData(peripheralID, this.writeQueue[0]); ---> Recursive call
}, 500);
}
// ...
}
多次调用 sendData 的问题可以通过删除递归来解决
这是一个示例,其中两个定时器回调都计划在 500 毫秒后发生,并且快速连续到达:
function example(a) { console.log("example:", a, "at", Date.now()); if (a <= 3) { setTimeout(() => { example(a * 2); }, 500); } } // Schedule the calls example(2); example(3); // Keep the thread busy const end = Date.now() + 600; while (Date.now() < end) { }
注意如何
example: 4 at 1597923771329 example: 6 at 1597923771330
在时间上彼此相邻。
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