WIP

Author: retronym

src/reflect/scala/reflect/internal/util/ChromeTrace.scala

@@ -3,8 +3,11 @@ package scala.reflect.internal.util
 import java.io.Closeable
 import java.lang.management.ManagementFactory
 import java.nio.file.{Files, Path}
+import java.util
 import java.util.concurrent.TimeUnit
 
+import scala.collection.mutable
+
 object ChromeTrace {
 
   private object EventType {
@@ -27,24 +30,29 @@ object ChromeTrace {
 final class ChromeTrace(f: Path) extends Closeable {
   import ChromeTrace.EventType
   private val traceWriter = Files.newBufferedWriter(f)
+  private val context = mutable.ArrayStack[JsonContext](TopContext)
+  private val tidCache = new ThreadLocal[String]() {
+    override def initialValue(): String = Thread.currentThread().getId.formatted("%05d")
+  }
   objStart()
   fld("traceEvents")
+  context.push(ValueContext)
   arrStart()
   traceWriter.write("\n")
 
-  private val pid = ManagementFactory.getRuntimeMXBean().getName()
+  private val pid = ManagementFactory.getRuntimeMXBean().getName().replaceAll("@.*", "")
 
   override def close(): Unit = {
-    traceWriter.append("\n")
     arrEnd()
     objEnd()
+    context.pop()
+    tidCache.remove()
     traceWriter.close()
   }
 
   def traceDurationEvent(name: String, startNanos: Long, durationNanos: Long, tid: String = this.tid()): Unit = {
     val durationMicros = nanosToMicros(durationNanos)
     val startMicros = nanosToMicros(startNanos)
-    commaIfFirst()
     objStart()
     str("cat", "scalac")
     str("name", name)
@@ -58,7 +66,6 @@ final class ChromeTrace(f: Path) extends Closeable {
   }
 
   def traceCounterEvent(name: String, counterName: String, count: Long): Unit = {
-    commaIfFirst()
     objStart()
     str("cat", "scalac")
     str("name", name)
@@ -78,7 +85,6 @@ final class ChromeTrace(f: Path) extends Closeable {
   def traceDurationEventEnd(name: String, colour: String = ""): Unit = traceAsyncEvent(EventType.Finished, name, colour)
 
   private def traceAsyncEvent(eventType: String, name: String, colour: String): Unit = {
-    commaIfFirst()
     objStart()
     str("cat", "scalac")
     str("name", name)
@@ -93,20 +99,21 @@ final class ChromeTrace(f: Path) extends Closeable {
     traceWriter.write("\n")
   }
 
-  private def tid() = Thread.currentThread().getId.toString
+  private def tid(): String = tidCache.get()
 
   private def nanosToMicros(t: Long): Long = TimeUnit.NANOSECONDS.toMicros(t)
 
   private def microTime(): Long = nanosToMicros(System.nanoTime())
 
-  private def commaIfFirst(): Unit = {
-    if (firstEvent) firstEvent = false else traceWriter.write(",")
-  }
-
-  private var firstEvent = true
+  sealed abstract class JsonContext
+  case class ArrayContext(var first: Boolean) extends JsonContext
+  case class ObjectContext(var first: Boolean) extends JsonContext
+  case object ValueContext extends JsonContext
+  case object TopContext extends JsonContext
 
   private def str(name: String, value: String): Unit = {
     fld(name)
+    traceWriter.write("\"")
     traceWriter.write(value) // This assumes no escaping is needed
     traceWriter.write("\"")
   }
@@ -115,15 +122,40 @@ final class ChromeTrace(f: Path) extends Closeable {
     traceWriter.write(String.valueOf(value))
     traceWriter.write("")
   }
-  private def objStart(): Unit = traceWriter.write("{")
-  private def objEnd(): Unit = traceWriter.write("}")
-  private def arrStart(): Unit = traceWriter.write("[")
-  private def arrEnd(): Unit = traceWriter.write("]")
+  private def objStart(): Unit = {
+    context.top match {
+      case ac @ ArrayContext(first) =>
+        if (first) ac.first = false
+        else traceWriter.write(",")
+      case _ =>
+    }
+    context.push(ObjectContext(true))
+    traceWriter.write("{")
+  }
+  private def objEnd(): Unit = {
+    traceWriter.write("}")
+    context.pop()
+  }
+  private def arrStart(): Unit = {
+    traceWriter.write("[")
+    context.push(ArrayContext(true))
+  }
+  private def arrEnd(): Unit = {
+    traceWriter.write("]")
+    context.pop()
+  }
 
   private def fld(name: String) = {
+    context.top match {
+      case oc @ ObjectContext(first) =>
+        if (first) oc.first = false
+        else traceWriter.write(",")
+      case context =>
+        throw new IllegalStateException("Wrong context: " + context)
+    }
     traceWriter.write("\"")
     traceWriter.write(name)
     traceWriter.write("\"")
-    traceWriter.write(": ")
+    traceWriter.write(":")
   }
 }