1 files changed, 69 insertions, 0 deletions
diff --git a/tracinglib/src/com/android/app/tracing/TraceContextElement.kt b/tracinglib/src/com/android/app/tracing/TraceContextElement.kt
new file mode 100644
index 0000000..2c952e1
--- /dev/null
+++ b/tracinglib/src/com/android/app/tracing/TraceContextElement.kt
@@ -0,0 +1,69 @@
+/*
+ * Copyright (C) 2023 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.app.tracing
+
+import com.android.app.tracing.TraceUtils.Companion.instant
+import com.android.app.tracing.TraceUtils.Companion.traceCoroutine
+import kotlin.coroutines.CoroutineContext
+import kotlinx.coroutines.CopyableThreadContextElement
+import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.DelicateCoroutinesApi
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+
+/**
+ * Used for safely persisting [TraceData] state when coroutines are suspended and resumed.
+ *
+ * This is internal machinery for [traceCoroutine]. It cannot be made `internal` or `private`
+ * because [traceCoroutine] is a Public-API inline function.
+ *
+ * @see traceCoroutine
+ */
+@OptIn(DelicateCoroutinesApi::class)
+@ExperimentalCoroutinesApi
+class TraceContextElement(private val traceData: TraceData = TraceData()) :
+    CopyableThreadContextElement<TraceData?> {
+
+    companion object Key : CoroutineContext.Key<TraceContextElement>
+
+    override val key: CoroutineContext.Key<TraceContextElement> = Key
+
+    @OptIn(ExperimentalStdlibApi::class)
+    override fun updateThreadContext(context: CoroutineContext): TraceData? {
+        val oldState = threadLocalTrace.get()
+        oldState?.endAllOnThread()
+        threadLocalTrace.set(traceData)
+        instant("resuming ${context[CoroutineDispatcher]}")
+        traceData.beginAllOnThread()
+        return oldState
+    }
+
+    @OptIn(ExperimentalStdlibApi::class)
+    override fun restoreThreadContext(context: CoroutineContext, oldState: TraceData?) {
+        instant("suspending ${context[CoroutineDispatcher]}")
+        traceData.endAllOnThread()
+        threadLocalTrace.set(oldState)
+        oldState?.beginAllOnThread()
+    }
+
+    override fun copyForChild(): CopyableThreadContextElement<TraceData?> {
+        return TraceContextElement(traceData.copy())
+    }
+
+    override fun mergeForChild(overwritingElement: CoroutineContext.Element): CoroutineContext {
+        return TraceContextElement(traceData.copy())
+    }
+}