Honor the parallel flag in the Analyzer

gzm0 · gzm0 · commit 9a0143c65542 · 2023-08-27T09:34:52.000+02:00
diff --git a/linker/js/src/main/scala/org/scalajs/linker/analyzer/Platform.scala b/linker/js/src/main/scala/org/scalajs/linker/analyzer/Platform.scala
@@ -13,7 +13,13 @@
 package org.scalajs.linker.analyzer
 
 import scala.collection.mutable
+import scala.concurrent.ExecutionContext
 
 private[analyzer] object Platform {
   def emptyThreadSafeMap[K, V]: mutable.Map[K, V] = mutable.Map.empty
+
+  def adjustExecutionContextForParallelism(ec: ExecutionContext,
+      parallel: Boolean): ExecutionContext = {
+    ec // we're never parallel on JS
+  }
 }
diff --git a/linker/jvm/src/main/scala/org/scalajs/linker/analyzer/Platform.scala b/linker/jvm/src/main/scala/org/scalajs/linker/analyzer/Platform.scala
@@ -14,7 +14,23 @@ package org.scalajs.linker.analyzer
 
 import scala.collection.mutable
 import scala.collection.concurrent.TrieMap
+import scala.concurrent.ExecutionContext
+
+import java.util.concurrent.Executors
 
 private[analyzer] object Platform {
   def emptyThreadSafeMap[K, V]: mutable.Map[K, V] = TrieMap.empty
+
+  def adjustExecutionContextForParallelism(ec: ExecutionContext,
+      parallel: Boolean): ExecutionContext = {
+    /* Parallel is the default. Parallelism is disabled (likely for debugging),
+     * we create our own single thread executor. This is for sure not the most
+     * efficient, but it is simpler than, say, attempting to build single thread
+     * execution on top of an arbitrary execution context.
+     * Further, if parallel is false, we do not expect that speed is the primary
+     * aim of the execution.
+     */
+    if (parallel) ec
+    else ExecutionContext.fromExecutorService(Executors.newSingleThreadExecutor())
+  }
 }
diff --git a/linker/shared/src/main/scala/org/scalajs/linker/analyzer/Analyzer.scala b/linker/shared/src/main/scala/org/scalajs/linker/analyzer/Analyzer.scala
@@ -37,7 +37,7 @@ import org.scalajs.linker.standard.ModuleSet.ModuleID
 
 import org.scalajs.logging._
 
-import Platform.emptyThreadSafeMap
+import Platform._
 
 import Analysis._
 import Infos.{NamespacedMethodName, ReachabilityInfo, ReachabilityInfoInClass}
@@ -74,6 +74,14 @@ final class Analyzer(config: CommonPhaseConfig, initial: Boolean,
   def computeReachability(moduleInitializers: Seq[ModuleInitializer],
       symbolRequirements: SymbolRequirement, logger: Logger)(implicit ec: ExecutionContext): Future[Analysis] = {
 
+    computeInternal(moduleInitializers, symbolRequirements, logger)(
+        adjustExecutionContextForParallelism(ec, config.parallel))
+  }
+
+  /** Internal helper to isolate the execution context. */
+  private def computeInternal(moduleInitializers: Seq[ModuleInitializer],
+      symbolRequirements: SymbolRequirement, logger: Logger)(implicit ec: ExecutionContext): Future[Analysis] = {
+
     resetState()
 
     infoLoader.update(logger)
