背景
最近在看SurfaceSyncGroup，很多代碼還是很好理解的，但是其中有幾處細節(jié)，可能你看的時候沒有注意。
因為這個SurfaceSyncGroup名字太長，我后面都會使用SSG縮寫代替。
一、跨進程使用SSG，無法支持Child SSG添加Child SSG
如果你看過代碼，你應(yīng)該可以發(fā)現(xiàn)，如果你在同一進程中使用SSG，其實是可以如下操作的。
但是如果跨進程使用，那就要注意了，可能就會有問題了，你以為你創(chuàng)建的是這樣子關(guān)系
其實你創(chuàng)建的關(guān)系和你預(yù)期的不一樣。
代碼分析1.1
public boolean add(ISurfaceSyncGroup surfaceSyncGroup, boolean parentSyncGroupMerge,
@Nullable Runnable runnable) {
//1.1如果添加的surfaceSyncGroup和當(dāng)前SurfaceSyncGroup不是同一進程，就是false。
if (isLocalBinder(surfaceSyncGroup.asBinder())) {
boolean didAddLocalSync = addLocalSync(surfaceSyncGroup, parentSyncGroupMerge);
if (Trace.isTagEnabled(Trace.TRACE_TAG_VIEW)) {
Trace.asyncTraceForTrackEnd(Trace.TRACE_TAG_VIEW, mTrackName, hashCode());
}
return didAddLocalSync;
}
synchronized (mLock) {
if (!mHasWMSync) {
// We need to add a signal into WMS since WMS will be creating a new parent
// SurfaceSyncGroup. When the parent SSG in WMS completes, only then do we
// notify the registered listeners that the entire SurfaceSyncGroup is complete.
// This is because the callers don't realize that when adding a different process
// to this SSG, it isn't actually adding to this SSG and really just creating a
// link in WMS. Because of this, the callers would expect the complete listeners
// to only be called when everything, including the other process's
// SurfaceSyncGroups, have completed. Only WMS has that info so we need to send the
// listener to WMS when we set up a server side sync.
mSurfaceSyncGroupCompletedListener = new ISurfaceSyncGroupCompletedListener.Stub() {
@Override
public void onSurfaceSyncGroupComplete() {
synchronized (mLock) {
invokeSyncCompleteCallbacks();
}
}
};
// 1.1.2 然后用自己的token在WM中創(chuàng)建一個替身
if (!addSyncToWm(mToken, false /* parentSyncGroupMerge */,
mSurfaceSyncGroupCompletedListener)) {//跳轉(zhuǎn)到代碼分析1.2
mSurfaceSyncGroupCompletedListener = null;
if (Trace.isTagEnabled(Trace.TRACE_TAG_VIEW)) {
Trace.asyncTraceForTrackEnd(Trace.TRACE_TAG_VIEW, mTrackName, hashCode());
}
return false;
}
mHasWMSync = true;
}
}
try {
// 1.1.3 將token傳遞給子ssg，然后讓子的ssg和你的替身建立關(guān)系
surfaceSyncGroup.onAddedToSyncGroup(mToken, parentSyncGroupMerge);
} catch (RemoteException e) {
if (Trace.isTagEnabled(Trace.TRACE_TAG_VIEW)) {
Trace.asyncTraceForTrackEnd(Trace.TRACE_TAG_VIEW, mTrackName, hashCode());
}
return false;
}
if (Trace.isTagEnabled(Trace.TRACE_TAG_VIEW)) {
Trace.asyncTraceForTrackEnd(Trace.TRACE_TAG_VIEW, mTrackName, hashCode());
}
return true;
}
1.1.1 如果添加的surfaceSyncGroup和當(dāng)前SurfaceSyncGroup不是同一進程，就是false。
1.1.2 然后用自己的token在WM中創(chuàng)建一個替身ssg
1.1.3 將token傳遞給子ssg，然后讓子的ssg和你的替身建立關(guān)系
代碼分析1.2
當(dāng)SSG1調(diào)用add(SSG2)的時候，SSG1和SSG2都會觸發(fā)這個函數(shù)。
1.2.1 將自己和WM中的替身建立起關(guān)系。如果是SSG1，也就意味著和之前Root SSG建立的關(guān)系也就斷開了。
private boolean addSyncToWm(IBinder token, boolean parentSyncGroupMerge,
@Nullable ISurfaceSyncGroupCompletedListener surfaceSyncGroupCompletedListener) {
try {
if (DEBUG) {
Log.d(TAG, "Attempting to add remote sync to " + mName
+ ". Setting up Sync in WindowManager.");
}
if (Trace.isTagEnabled(Trace.TRACE_TAG_VIEW)) {
Trace.asyncTraceForTrackBegin(Trace.TRACE_TAG_VIEW, mTrackName,
"addSyncToWm=" + token.hashCode(), hashCode());
}
AddToSurfaceSyncGroupResult addToSyncGroupResult = new AddToSurfaceSyncGroupResult();
if (!WindowManagerGlobal.getWindowManagerService().addToSurfaceSyncGroup(token,
parentSyncGroupMerge, surfaceSyncGroupCompletedListener,
addToSyncGroupResult)) {
if (Trace.isTagEnabled(Trace.TRACE_TAG_VIEW)) {
Trace.asyncTraceForTrackEnd(Trace.TRACE_TAG_VIEW, mTrackName, hashCode());
}
return false;
}
//1.2.1 將自己和WM中的替身建立起關(guān)系。如果是SSG1，也就意味著和之前Root SSG建立的關(guān)系也就斷開了。
setTransactionCallbackFromParent(addToSyncGroupResult.mParentSyncGroup,
addToSyncGroupResult.mTransactionReadyCallback);
} catch (RemoteException e) {
if (Trace.isTagEnabled(Trace.TRACE_TAG_VIEW)) {
Trace.asyncTraceForTrackEnd(Trace.TRACE_TAG_VIEW, mTrackName, hashCode());
}
return false;
}
if (Trace.isTagEnabled(Trace.TRACE_TAG_VIEW)) {
Trace.asyncTraceForTrackEnd(Trace.TRACE_TAG_VIEW, mTrackName, hashCode());
}
return true;
}
最終的結(jié)果如下圖
當(dāng)SSG1添加到Root SSG的時候，一切還算正常
但是當(dāng)SSG2添加到SSG1的時候，意外就發(fā)生了，Root SSG和SSG1就斷開了連接。
二、如果SSG1添加到Root SSG之后，將SSG1添加到 SSG2，會發(fā)生什么
代碼分析2.1
private void setTransactionCallbackFromParent(ISurfaceSyncGroup parentSyncGroup,
ITransactionReadyCallback transactionReadyCallback) {
...
synchronized (mLock) {
if (mFinished) {
finished = true;
} else {
// If this SurfaceSyncGroup was already added to a different SurfaceSyncGroup, we
// need to combine everything. We can add the old SurfaceSyncGroup parent to the new
// parent so the new parent doesn't complete until the old parent does.
// Additionally, the old parent will not get the final transaction object and
// instead will send it to the new parent, ensuring that any other SurfaceSyncGroups
// from the original parent are also combined with the new parent SurfaceSyncGroup.
// 2.1.1 如果發(fā)現(xiàn)SSG1有parent SSG了， 就將parent ssg（Root SSG）添加到SSG2
if (mParentSyncGroup != null && mParentSyncGroup != parentSyncGroup) {
if (DEBUG) {
Log.d(TAG, "Trying to add to " + parentSyncGroup
+ " but already part of sync group " + mParentSyncGroup + " "
+ mName);
}
try {
//最終會跳轉(zhuǎn)到代碼分析 2.2
parentSyncGroup.addToSync(mParentSyncGroup,
true /* parentSyncGroupMerge */);
} catch (RemoteException e) {
}
}
if (DEBUG && mParentSyncGroup == parentSyncGroup) {
Log.d(TAG, "Added to parent that was already the parent");
}
// 2.1.2 保存前一個parent ssg（Root SSG）的callback。
Consumer<Transaction> lastCallback = mTransactionReadyConsumer;
// 2.1.3 將parent ssg 換成 SSG2
mParentSyncGroup = parentSyncGroup;
mTransactionReadyConsumer = (transaction) -> {
if (Trace.isTagEnabled(Trace.TRACE_TAG_VIEW)) {
Trace.asyncTraceForTrackBegin(Trace.TRACE_TAG_VIEW, mTrackName,
"Invoke transactionReadyCallback="
+ transactionReadyCallback.hashCode(), hashCode());
}
// 2.1.4 在SSG1完成任務(wù)的時候，雖然SSG1和Root SSG沒有名義上的關(guān)系了，但是殘留在Root SSG mPendingSyncs中SSG1的callback還是要觸發(fā)一下的，否則會導(dǎo)致Root SSG無法ready。
lastCallback.accept(null);
try {
transactionReadyCallback.onTransactionReady(transaction);
} catch (RemoteException e) {
transaction.apply();
}
if (Trace.isTagEnabled(Trace.TRACE_TAG_VIEW)) {
Trace.asyncTraceForTrackEnd(Trace.TRACE_TAG_VIEW, mTrackName, hashCode());
}
};
addedToSyncListener = mAddedToSyncListener;
}
}
// Invoke the callback outside of the lock when the SurfaceSyncGroup being added was already
// complete.
if (finished) {
try {
transactionReadyCallback.onTransactionReady(null);
} catch (RemoteException e) {
}
} else if (addedToSyncListener != null) {
addedToSyncListener.run();
}
if (Trace.isTagEnabled(Trace.TRACE_TAG_VIEW)) {
Trace.asyncTraceForTrackEnd(Trace.TRACE_TAG_VIEW, mTrackName, hashCode());
}
}
2.1.1 如果發(fā)現(xiàn)SSG1有parent SSG了， 就將parent ssg（Root SSG）添加到SSG2
2.1.2 保存前一個parent ssg（Root SSG）的callback。
2.1.3 將parent ssg 換成 SSG2
2.1.4 在SSG1完成任務(wù)的時候，雖然SSG1和Root SSG沒有名義上的關(guān)系了，但是殘留在Root SSG mPendingSyncs中SSG1的callback還是要觸發(fā)一下的，否則會導(dǎo)致Root SSG無法ready。
代碼分析 2.2
代碼分析2.1中parentSyncGroup.addToSync(mParentSyncGroup, true /* parentSyncGroupMerge */)最終會跳轉(zhuǎn)到這里，關(guān)鍵的就是parentSyncGroupMerge為true
public ITransactionReadyCallback createTransactionReadyCallback(boolean parentSyncGroupMerge) {
ITransactionReadyCallback transactionReadyCallback =
new ITransactionReadyCallback.Stub() {
@Override
public void onTransactionReady(Transaction t) {
synchronized (mLock) {
if (t != null) {
t.sanitize(Binder.getCallingPid(), Binder.getCallingUid());
// When an older parent sync group is added due to a child syncGroup
// getting added to multiple groups, we need to maintain merge order
// so the older parentSyncGroup transactions are overwritten by
// anything in the newer parentSyncGroup.
// 2.2.1 這里解釋了如果為true，為了保證merge的順序，有一些處理。
if (parentSyncGroupMerge) {
t.merge(mTransaction);
}
mTransaction.merge(t);//p add c
}
mPendingSyncs.remove(this);
if (Trace.isTagEnabled(Trace.TRACE_TAG_VIEW)) {
Trace.instantForTrack(Trace.TRACE_TAG_VIEW, mTrackName,
"onTransactionReady callback=" + hashCode());
}
checkIfSyncIsComplete();
}
}
};
return transactionReadyCallback;
}
2.2.1 這里解釋了如果為true，為了保證merge的順序，有一些處理，用一個圖來表示，就是如下圖。
三、總結(jié)
SurfaceSyncGroup代碼不是很多，但是使用時候要注意這些細節(jié)，避免發(fā)生錯誤，具體講解SurfaceSyncGroup配合BBQ和BlastSyncEngine工作，我還是會選擇使用圖解視頻的方式，給自己留個坑《王小二圖解Android-SurfaceSyncGroup》
