diff --git a/services/core/java/com/android/server/am/ActivityTaskManagerService.java b/services/core/java/com/android/server/am/ActivityTaskManagerService.java
new file mode 100644
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+++ b/services/core/java/com/android/server/am/ActivityTaskManagerService.java
@@ -0,0 +1,309 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License
+ */
+
+package com.android.server.am;
+
+import static android.Manifest.permission.MANAGE_ACTIVITY_STACKS;
+import static android.app.ActivityTaskManager.SPLIT_SCREEN_CREATE_MODE_TOP_OR_LEFT;
+import static android.app.WindowConfiguration.ACTIVITY_TYPE_UNDEFINED;
+import static android.app.WindowConfiguration.WINDOWING_MODE_PINNED;
+import static android.app.WindowConfiguration.WINDOWING_MODE_SPLIT_SCREEN_PRIMARY;
+import static android.app.WindowConfiguration.WINDOWING_MODE_UNDEFINED;
+import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_ALL;
+import static com.android.server.am.ActivityManagerDebugConfig.DEBUG_STACK;
+import static com.android.server.am.ActivityManagerDebugConfig.POSTFIX_STACK;
+import static com.android.server.am.ActivityManagerDebugConfig.TAG_AM;
+import static com.android.server.am.ActivityManagerDebugConfig.TAG_WITH_CLASS_NAME;
+import static com.android.server.am.ActivityManagerService.ANIMATE;
+import static com.android.server.am.ActivityStackSupervisor.DEFER_RESUME;
+import static com.android.server.am.TaskRecord.REPARENT_KEEP_STACK_AT_FRONT;
+
+import android.app.ActivityManager;
+import android.app.IActivityTaskManager;
+import android.app.WindowConfiguration;
+import android.content.Context;
+import android.graphics.Rect;
+import android.os.Binder;
+import android.util.Slog;
+
+import com.android.server.SystemService;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * System service for managing activities and their containers (task, stacks, displays,... ).
+ *
+ * {@hide}
+ */
+public class ActivityTaskManagerService extends IActivityTaskManager.Stub {
+    private static final String TAG = TAG_WITH_CLASS_NAME ? "ActivityTaskManagerService" : TAG_AM;
+    private static final String TAG_STACK = TAG + POSTFIX_STACK;
+
+    private Context mContext;
+    private ActivityManagerService mAm;
+    /* Global service lock used by the package the owns this service. */
+    Object mGlobalLock;
+    private ActivityStackSupervisor mStackSupervisor;
+
+    ActivityTaskManagerService(Context context) {
+        mContext = context;
+    }
+
+    // TODO: Will be converted to WM lock once transition is complete.
+    void setActivityManagerService(ActivityManagerService am) {
+        mAm = am;
+        mGlobalLock = mAm;
+        mStackSupervisor = mAm.mStackSupervisor;
+    }
+
+    public static final class Lifecycle extends SystemService {
+        private final ActivityTaskManagerService mService;
+
+        public Lifecycle(Context context) {
+            super(context);
+            mService = new ActivityTaskManagerService(context);
+        }
+
+        @Override
+        public void onStart() {
+            publishBinderService(Context.ACTIVITY_TASK_SERVICE, mService);
+        }
+
+        public ActivityTaskManagerService getService() {
+            return mService;
+        }
+    }
+
+    @Override
+    public void setTaskWindowingMode(int taskId, int windowingMode, boolean toTop) {
+        if (windowingMode == WINDOWING_MODE_SPLIT_SCREEN_PRIMARY) {
+            setTaskWindowingModeSplitScreenPrimary(taskId, SPLIT_SCREEN_CREATE_MODE_TOP_OR_LEFT,
+                    toTop, ANIMATE, null /* initialBounds */, true /* showRecents */);
+            return;
+        }
+        mAm.enforceCallerIsRecentsOrHasPermission(MANAGE_ACTIVITY_STACKS, "setTaskWindowingMode()");
+        synchronized (mGlobalLock) {
+            final long ident = Binder.clearCallingIdentity();
+            try {
+                final TaskRecord task = mStackSupervisor.anyTaskForIdLocked(taskId);
+                if (task == null) {
+                    Slog.w(TAG, "setTaskWindowingMode: No task for id=" + taskId);
+                    return;
+                }
+
+                if (DEBUG_STACK) Slog.d(TAG_STACK, "setTaskWindowingMode: moving task=" + taskId
+                        + " to windowingMode=" + windowingMode + " toTop=" + toTop);
+
+                if (!task.isActivityTypeStandardOrUndefined()) {
+                    throw new IllegalArgumentException("setTaskWindowingMode: Attempt to move"
+                            + " non-standard task " + taskId + " to windowing mode="
+                            + windowingMode);
+                }
+
+                final ActivityStack stack = task.getStack();
+                if (toTop) {
+                    stack.moveToFront("setTaskWindowingMode", task);
+                }
+                stack.setWindowingMode(windowingMode);
+            } finally {
+                Binder.restoreCallingIdentity(ident);
+            }
+        }
+    }
+
+    @Override
+    public List<ActivityManager.RunningTaskInfo> getTasks(int maxNum) {
+        return getFilteredTasks(maxNum, ACTIVITY_TYPE_UNDEFINED, WINDOWING_MODE_UNDEFINED);
+    }
+
+    @Override
+    public List<ActivityManager.RunningTaskInfo> getFilteredTasks(int maxNum,
+            @WindowConfiguration.ActivityType int ignoreActivityType,
+            @WindowConfiguration.WindowingMode int ignoreWindowingMode) {
+        final int callingUid = Binder.getCallingUid();
+        ArrayList<ActivityManager.RunningTaskInfo> list = new ArrayList<>();
+
+        synchronized (mGlobalLock) {
+            if (DEBUG_ALL) Slog.v(TAG, "getTasks: max=" + maxNum);
+
+            final boolean allowed = mAm.isGetTasksAllowed("getTasks", Binder.getCallingPid(),
+                    callingUid);
+            mStackSupervisor.getRunningTasks(maxNum, list, ignoreActivityType,
+                    ignoreWindowingMode, callingUid, allowed);
+        }
+
+        return list;
+    }
+
+    @Override
+    public void moveTaskToStack(int taskId, int stackId, boolean toTop) {
+        mAm.enforceCallerIsRecentsOrHasPermission(MANAGE_ACTIVITY_STACKS, "moveTaskToStack()");
+        synchronized (mGlobalLock) {
+            final long ident = Binder.clearCallingIdentity();
+            try {
+                final TaskRecord task = mStackSupervisor.anyTaskForIdLocked(taskId);
+                if (task == null) {
+                    Slog.w(TAG, "moveTaskToStack: No task for id=" + taskId);
+                    return;
+                }
+
+                if (DEBUG_STACK) Slog.d(TAG_STACK, "moveTaskToStack: moving task=" + taskId
+                        + " to stackId=" + stackId + " toTop=" + toTop);
+
+                final ActivityStack stack = mStackSupervisor.getStack(stackId);
+                if (stack == null) {
+                    throw new IllegalStateException(
+                            "moveTaskToStack: No stack for stackId=" + stackId);
+                }
+                if (!stack.isActivityTypeStandardOrUndefined()) {
+                    throw new IllegalArgumentException("moveTaskToStack: Attempt to move task "
+                            + taskId + " to stack " + stackId);
+                }
+                if (stack.inSplitScreenPrimaryWindowingMode()) {
+                    mAm.mWindowManager.setDockedStackCreateState(
+                            SPLIT_SCREEN_CREATE_MODE_TOP_OR_LEFT, null /* initialBounds */);
+                }
+                task.reparent(stack, toTop, REPARENT_KEEP_STACK_AT_FRONT, ANIMATE, !DEFER_RESUME,
+                        "moveTaskToStack");
+            } finally {
+                Binder.restoreCallingIdentity(ident);
+            }
+        }
+    }
+
+    @Override
+    public void resizeStack(int stackId, Rect destBounds, boolean allowResizeInDockedMode,
+            boolean preserveWindows, boolean animate, int animationDuration) {
+        mAm.enforceCallerIsRecentsOrHasPermission(MANAGE_ACTIVITY_STACKS, "resizeStack()");
+
+        final long ident = Binder.clearCallingIdentity();
+        try {
+            synchronized (mGlobalLock) {
+                if (animate) {
+                    final PinnedActivityStack stack = mStackSupervisor.getStack(stackId);
+                    if (stack == null) {
+                        Slog.w(TAG, "resizeStack: stackId " + stackId + " not found.");
+                        return;
+                    }
+                    if (stack.getWindowingMode() != WINDOWING_MODE_PINNED) {
+                        throw new IllegalArgumentException("Stack: " + stackId
+                                + " doesn't support animated resize.");
+                    }
+                    stack.animateResizePinnedStack(null /* sourceHintBounds */, destBounds,
+                            animationDuration, false /* fromFullscreen */);
+                } else {
+                    final ActivityStack stack = mStackSupervisor.getStack(stackId);
+                    if (stack == null) {
+                        Slog.w(TAG, "resizeStack: stackId " + stackId + " not found.");
+                        return;
+                    }
+                    mStackSupervisor.resizeStackLocked(stack, destBounds,
+                            null /* tempTaskBounds */, null /* tempTaskInsetBounds */,
+                            preserveWindows, allowResizeInDockedMode, !DEFER_RESUME);
+                }
+            }
+        } finally {
+            Binder.restoreCallingIdentity(ident);
+        }
+    }
+
+    /**
+     * Moves the specified task to the primary-split-screen stack.
+     *
+     * @param taskId Id of task to move.
+     * @param createMode The mode the primary split screen stack should be created in if it doesn't
+     *                   exist already. See
+     *                   {@link android.app.ActivityTaskManager#SPLIT_SCREEN_CREATE_MODE_TOP_OR_LEFT}
+     *                   and
+     *                   {@link android.app.ActivityTaskManager#SPLIT_SCREEN_CREATE_MODE_BOTTOM_OR_RIGHT}
+     * @param toTop If the task and stack should be moved to the top.
+     * @param animate Whether we should play an animation for the moving the task.
+     * @param initialBounds If the primary stack gets created, it will use these bounds for the
+     *                      stack. Pass {@code null} to use default bounds.
+     * @param showRecents If the recents activity should be shown on the other side of the task
+     *                    going into split-screen mode.
+     */
+    @Override
+    public boolean setTaskWindowingModeSplitScreenPrimary(int taskId, int createMode,
+            boolean toTop, boolean animate, Rect initialBounds, boolean showRecents) {
+        mAm.enforceCallerIsRecentsOrHasPermission(MANAGE_ACTIVITY_STACKS,
+                "setTaskWindowingModeSplitScreenPrimary()");
+        synchronized (mGlobalLock) {
+            final long ident = Binder.clearCallingIdentity();
+            try {
+                final TaskRecord task = mStackSupervisor.anyTaskForIdLocked(taskId);
+                if (task == null) {
+                    Slog.w(TAG, "setTaskWindowingModeSplitScreenPrimary: No task for id=" + taskId);
+                    return false;
+                }
+                if (DEBUG_STACK) Slog.d(TAG_STACK,
+                        "setTaskWindowingModeSplitScreenPrimary: moving task=" + taskId
+                                + " to createMode=" + createMode + " toTop=" + toTop);
+                if (!task.isActivityTypeStandardOrUndefined()) {
+                    throw new IllegalArgumentException("setTaskWindowingMode: Attempt to move"
+                            + " non-standard task " + taskId + " to split-screen windowing mode");
+                }
+
+                mAm.mWindowManager.setDockedStackCreateState(createMode, initialBounds);
+                final int windowingMode = task.getWindowingMode();
+                final ActivityStack stack = task.getStack();
+                if (toTop) {
+                    stack.moveToFront("setTaskWindowingModeSplitScreenPrimary", task);
+                }
+                stack.setWindowingMode(WINDOWING_MODE_SPLIT_SCREEN_PRIMARY, animate, showRecents,
+                        false /* enteringSplitScreenMode */, false /* deferEnsuringVisibility */);
+                return windowingMode != task.getWindowingMode();
+            } finally {
+                Binder.restoreCallingIdentity(ident);
+            }
+        }
+    }
+
+    /**
+     * Removes stacks in the input windowing modes from the system if they are of activity type
+     * ACTIVITY_TYPE_STANDARD or ACTIVITY_TYPE_UNDEFINED
+     */
+    @Override
+    public void removeStacksInWindowingModes(int[] windowingModes) {
+        mAm.enforceCallerIsRecentsOrHasPermission(MANAGE_ACTIVITY_STACKS,
+                "removeStacksInWindowingModes()");
+
+        synchronized (mGlobalLock) {
+            final long ident = Binder.clearCallingIdentity();
+            try {
+                mStackSupervisor.removeStacksInWindowingModes(windowingModes);
+            } finally {
+                Binder.restoreCallingIdentity(ident);
+            }
+        }
+    }
+
+    @Override
+    public void removeStacksWithActivityTypes(int[] activityTypes) {
+        mAm.enforceCallerIsRecentsOrHasPermission(MANAGE_ACTIVITY_STACKS,
+                "removeStacksWithActivityTypes()");
+
+        synchronized (mGlobalLock) {
+            final long ident = Binder.clearCallingIdentity();
+            try {
+                mStackSupervisor.removeStacksWithActivityTypes(activityTypes);
+            } finally {
+                Binder.restoreCallingIdentity(ident);
+            }
+        }
+    }
+}