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This article focuses on "when Android threads will enter the waiting state", interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Next, let the editor take you to learn "under what circumstances will Android threads enter the waiting state"?

There are two situations, one is that when there is no message in the message queue, it will put the thread into a waiting state; the other is that there is a message in the message queue, but the message specifies the time of execution, and the thread will also enter the waiting state when it has not yet reached this time.

The messages in the message queue are sorted in chronological order, which we will see later when parsing the sending of messages.

The most important thing about this function is to get the next message to be processed from the message queue, that is, the MessageQueue.next function, which implements the following in the frameworks/base/core/java/android/os/MessageQueue.java file:

[java] view plaincopypublic class MessageQueue {

.

Final Message next () {

Int pendingIdleHandlerCount =-1; / /-1 only during first iteration

Int nextPollTimeoutMillis = 0

For (;;) {

If (nextPollTimeoutMillis! = 0) {

Binder.flushPendingCommands ()

}

NativePollOnce (mPtr, nextPollTimeoutMillis)

Synchronized (this) {

/ / Try to retrieve the next message. Return if found.

Final long now = SystemClock.uptimeMillis ()

Final Message msg = mMessages

If (msg! = null) {

Final long when = msg.when

If (now > = when) {

MBlocked = false

MMessages = msg.next

Msg.next = null

If (Config.LOGV) Log.v ("MessageQueue", "Returning message:" + msg)

Return msg

} else {

NextPollTimeoutMillis = (int) Math.min (when-now, Integer.MAX_VALUE)

}

} else {

NextPollTimeoutMillis =-1

}

/ / If first time, then get the number of idlers to run.

If (pendingIdleHandlerCount < 0) {

PendingIdleHandlerCount = mIdleHandlers.size ()

}

If (pendingIdleHandlerCount = = 0) {

/ / No idle handlers to run. Loop and wait some more.

MBlocked = true

Continue

}

If (mPendingIdleHandlers = = null) {

MPendingIdleHandlers = new IdleHandler [Math.max (pendingIdleHandlerCount)

]

}

MPendingIdleHandlers = mIdleHandlers.toArray (mPendingIdleHandlers)

}

/ / Run the idle handlers.

/ / We only ever reach this code block during the first iteration.

For (int I = 0; I < pendingIdleHandlerCount; iTunes +) {

Final IdleHandler idler = mPendingIdleHandlers [I]

MPendingIdleHandlers [I] = null; / / release the reference to the handler

Boolean keep = false

Try {

Keep = idler.queueIdle ()

} catch (Throwable t) {

Log.wtf ("MessageQueue", "IdleHandler threw exception", t)

}

If (! keep) {

Synchronized (this) {

MIdleHandlers.remove (idler)

}

}

}

/ / Reset the idle handler count to 0 so we do not run them again.

PendingIdleHandlerCount = 0

/ / While calling an idle handler, a new message could have been

Livered

/ / so go back and look again for a pending message without waiting.

NextPollTimeoutMillis = 0

}

}

.

}

Execute the following statement to see if there are any messages in the current message queue:

[java] view plaincopynativePollOnce (mPtr, nextPollTimeoutMillis)

This is a JNI method. We will analyze it later. The parameter mPtr passed here points to the NativeMessageQueue object we created in the JNI layer, while the parameter nextPollTimeoutMillis indicates that if there is no message in the current message queue, when it waits, the value passed in the for loop is 0, which means no wait.

At this point, I believe you have a deeper understanding of "when Android threads will enter the waiting state". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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