Add AutoPark template class and use to control FastMixer

Bug: 24667895
Change-Id: Id739a109aca13664b9390d2f9d9616fa2f88d188
diff --git a/services/audioflinger/AutoPark.h b/services/audioflinger/AutoPark.h
new file mode 100644
index 0000000..e539e47
--- /dev/null
+++ b/services/audioflinger/AutoPark.h
@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2016 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.
+ */
+
+namespace android {
+
+// T is FastMixer or FastCapture
+template<typename T> class AutoPark {
+public:
+
+    // Park the specific FastThread, which can be nullptr, in hot idle if not currently idling
+    AutoPark(const sp<T>& fastThread) : mFastThread(fastThread)
+    {
+        mPreviousCommand = FastThreadState::HOT_IDLE;
+        if (fastThread != nullptr) {
+            auto sq = mFastThread->sq();
+            FastThreadState *state = sq->begin();
+            if (!(state->mCommand & FastThreadState::IDLE)) {
+                mPreviousCommand = state->mCommand;
+                state->mCommand = FastThreadState::HOT_IDLE;
+                sq->end();
+                sq->push(sq->BLOCK_UNTIL_ACKED);
+            } else {
+                sq->end(false /*didModify*/);
+            }
+        }
+    }
+
+    // Remove the FastThread from hot idle if necessary
+    ~AutoPark()
+    {
+        if (!(mPreviousCommand & FastThreadState::IDLE)) {
+            ALOG_ASSERT(mFastThread != nullptr);
+            auto sq = mFastThread->sq();
+            FastThreadState *state = sq->begin();
+            ALOG_ASSERT(state->mCommand == FastThreadState::HOT_IDLE);
+            state->mCommand = mPreviousCommand;
+            sq->end();
+            sq->push(sq->BLOCK_UNTIL_PUSHED);
+        }
+    }
+
+private:
+    const sp<T>                 mFastThread;
+    // if !&IDLE, holds the FastThread state to restore after new parameters processed
+    FastThreadState::Command    mPreviousCommand;
+};  // class AutoPark
+
+}   // namespace