Android 中的 Handler 同步分割栏实现方法
程序员文章站
2022-05-01 17:53:48
handler异步实现控制message的处理的，异步线程可以在handler中设置异步卡子，设置好了以后，当前handler的同步message都不再执行，直到异步线程将卡子去掉。
一、posts...
handler异步实现控制message的处理的，异步线程可以在handler中设置异步卡子，设置好了以后，当前handler的同步message都不再执行，直到异步线程将卡子去掉。
一、postsyncbarrier 设置同步卡
方法是隐藏的需要反射获取 api版本<23方法位于looper中，api版本>23位于messagequeue中 作用是为handler设置卡子，过滤掉同步消息，同步消息等待执行
二、removesyncbarrier 移除同步卡
方法是隐藏的需要反射获取 api版本<23方法位于looper中，api版本>23位于messagequeue中 作用是为handler移除卡子，放开同步消息过滤，同步消息继续执行。
package qin.xue.imageviewscaletype.activity;
import android.app.activity;
import android.os.bundle;
import android.os.handler;
import android.os.handlerthread;
import android.os.looper;
import android.os.messagequeue;
import android.util.log;
import java.lang.reflect.method;
import qin.xue.imageviewscaletype.r;
/**
* created by qinxue on 2018/5/21.
*/
public class syncbarrieractivity extends activity {
private static final string tag = "syncbarrieractivity";
private handler handler;
private handler workhanlder;
private handlerthread workhandlerthread;
private method methodpostsyncbarrier;
private looper looper;
private int token;
private int count = 0;
private long start = 0;
private long end = 0;
@override
protected void oncreate(bundle savedinstancestate) {
super.oncreate(savedinstancestate);
setcontentview(r.layout.sync_barrier_activity_layout);
workhandlerthread = new handlerthread("work_thread");
workhandlerthread.start();
looper = workhandlerthread.getlooper();
workhanlder = new handler(looper);
handler = new handler();
workhanlder.post(runnable);
handler.post(new runnable() {
@override
public void run() {
start = system.currenttimemillis();
log.i(tag, "设置同步卡 时间：" + start);
postsyncbarrier(); //设置同步卡
}
});
handler.postdelayed(new runnable() {
@override
public void run() {
end = system.currenttimemillis();
log.i(tag, "移除同步卡 时间：" + end + "耗时：" + (end - start));
removesyncbarrier(); //5秒后移除同步卡
}
}, 5000);
}
//postsyncbarrier 和 removesyncbarrier 方法是否在messagequeue类中（api23及以上）
private static boolean methodinqueue() {
return android.os.build.version.sdk_int >= android.os.build.version_codes.m;
}
private runnable runnable = new runnable() {
@override
public void run() {
count++;
log.i(tag, "count: " + count + "time: " + system.currenttimemillis()); //同步打印数据
workhanlder.postdelayed(runnable, 100);
}
};
/**
* 移除卡子
*/
private void removesyncbarrier() {
if (android.os.build.version.sdk_int >= android.os.build.version_codes.m) {
removesyncbarrier(looper.getqueue());
} else {
removesyncbarrier(looper);
}
}
private void removesyncbarrier(object obj) {
try {
method method = messagequeue.class.getmethod("removesyncbarrier", int.class);
method.invoke(obj, token);
} catch (exception e) {
e.printstacktrace();
}
}
/**
* 添加卡子
*/
private void postsyncbarrier() {
if (methodinqueue()) {
postsyncbarrier(looper.getqueue());
} else {
postsyncbarrier(looper);
}
}
private void postsyncbarrier(object obj) {
try {
methodpostsyncbarrier = obj.getclass().getmethod("postsyncbarrier");
token = (int) methodpostsyncbarrier.invoke(obj);
} catch (exception e) {
e.printstacktrace();
}
}
}
三、结果展示
05-21 17:44:22.926 12715-12732/qin.xue.imageviewscaletype i/syncbarrieractivity: count: 1time: 1526895862926 05-21 17:44:22.947 12715-12715/qin.xue.imageviewscaletype i/syncbarrieractivity: 设置同步卡 时间：1526895862947 05-21 17:44:27.931 12715-12715/qin.xue.imageviewscaletype i/syncbarrieractivity: 移除同步卡 时间：1526895867930耗时：4983 05-21 17:44:27.932 12715-12732/qin.xue.imageviewscaletype i/syncbarrieractivity: count: 2time: 1526895867932 05-21 17:44:28.033 12715-12732/qin.xue.imageviewscaletype i/syncbarrieractivity: count: 3time: 1526895868033 05-21 17:44:28.134 12715-12732/qin.xue.imageviewscaletype i/syncbarrieractivity: count: 4time: 1526895868134 05-21 17:44:28.236 12715-12732/qin.xue.imageviewscaletype i/syncbarrieractivity: count: 5time: 1526895868235 05-21 17:44:28.336 12715-12732/qin.xue.imageviewscaletype i/syncbarrieractivity: count: 6time: 1526895868336 05-21 17:44:28.437 12715-12732/qin.xue.imageviewscaletype i/syncbarrieractivity: count: 7time: 1526895868437 05-21 17:44:28.538 12715-12732/qin.xue.imageviewscaletype i/syncbarrieractivity: count: 8time: 1526895868538 05-21 17:44:28.639 12715-12732/qin.xue.imageviewscaletype i/syncbarrieractivity: count: 9time: 1526895868639 05-21 17:44:28.739 12715-12732/qin.xue.imageviewscaletype i/syncbarrieractivity: count: 10time: 1526895868739 05-21 17:44:28.841 12715-12732/qin.xue.imageviewscaletype i/syncbarrieractivity: count: 11time: 1526895868841 05-21 17:44:28.941 12715-12732/qin.xue.imageviewscaletype i/syncbarrieractivity: count: 12time: 1526895868941 05-21 17:44:29.043 12715-12732/qin.xue.imageviewscaletype i/syncbarrieractivity: count: 13time: 1526895869043 05-21 17:44:29.144 12715-12732/qin.xue.imageviewscaletype i/syncbarrieractivity: count: 14time: 1526895869144 05-21 17:44:29.244 12715-12732/qin.xue.imageviewscaletype i/syncbarrieractivity: count: 15time: 1526895869244 05-21 17:44:29.345 12715-12732/qin.xue.imageviewscaletype i/syncbarrieractivity: count: 16time: 1526895869345
四、代码解释
代码中首先加了使用主线程设置异步线程workhandler中的异步卡子，导致workhandler中的message不在执行，仅保留待执行。 然后在5s之后在主线程移除了异步线程workhandler中的卡子，workhandler中的message继续执行下去。源码分析">五、源码分析
我这里是6.0的源码
postsyncbarrier
public int postsyncbarrier() {
return postsyncbarrier(systemclock.uptimemillis());
}
private int postsyncbarrier(long when) {
// enqueue a new sync barrier token.
// we don't need to wake the queue because the purpose of a barrier is to stall it.
synchronized (this) {
final int token = mnextbarriertoken++;
final message msg = message.obtain();
msg.markinuse();
msg.when = when;
msg.arg1 = token;
message prev = null;
message p = mmessages;
if (when != 0) {
while (p != null && p.when <= when) {
prev = p;
p = p.next;
}
}
if (prev != null) { // invariant: p == prev.next
msg.next = p;
prev.next = msg;
} else {
msg.next = p;
mmessages = msg;
}
return token;
}
}
-这里可以看到这个卡子msg，新建了一个msg并根据时间插入到消息队列中，而且这个msg没有设置target
removesyncbarrier
public void removesyncbarrier(int token) {
// remove a sync barrier token from the queue.
// if the queue is no longer stalled by a barrier then wake it.
synchronized (this) {
message prev = null;
message p = mmessages;
while (p != null && (p.target != null || p.arg1 != token)) {
prev = p;
p = p.next;
}
if (p == null) {
throw new illegalstateexception("the specified message queue synchronization "
+ " barrier token has not been posted or has already been removed.");
}
final boolean needwake;
if (prev != null) {
prev.next = p.next;
needwake = false;
} else {
mmessages = p.next;
needwake = mmessages == null || mmessages.target != null;
}
p.recycleunchecked();
// if the loop is quitting then it is already awake.
// we can assume mptr != 0 when mquitting is false.
if (needwake && !mquitting) {
nativewake(mptr);
}
}
}
-（p.target != null || p.arg1 != token）这里如果arg1 == token或者target为null，那么这是一个卡子。需要移除掉 ，代码如下。 prev.next = p.next;
next()
在messagequeue中还有这个方法，获取消息队列中的下一个message
if (msg != null && msg.target == null) {
// stalled by a barrier. find the next asynchronous message in the queue.
do {
prevmsg = msg;
msg = msg.next;
} while (msg != null && !msg.isasynchronous());
}
摘取部分代码，循环便利整个消息队列，如果target为null，那么直接利用isasynchronous()找到下一个异步的message，跳过同步消息，设置执行时间。
大致就是这样。
handler中还有阻塞机制
-如果发先下一条消息执行时间过长，会阻塞掉线程looper循环的。在c++层，下次再研究下。