Merge branch 'master' into constructor-tearoffs-smoke

Author: jcollins-g

lib/dartdoc.dart

@@ -262,7 +262,7 @@ class Dartdoc {
       return dartdocResults;
     } finally {
       // Clear out any cached tool snapshots and temporary directories.
-      SnapshotCache.instance?.dispose();
+      SnapshotCache.instanceFor(config.resourceProvider).dispose();
       // ignore: unawaited_futures
       ToolTempFileTracker.instance?.dispose();
     }

lib/src/tool_definition.dart

@@ -109,8 +109,8 @@ class DartToolDefinition extends ToolDefinition {
     assert(args[0] == command.first);
     // Set up flags to create a new snapshot, if needed, and use the first run
     // as the training run.
-    SnapshotCache.createInstance(_resourceProvider);
-    var snapshot = SnapshotCache.instance.getSnapshot(command.first);
+    var snapshotCache = SnapshotCache.instanceFor(_resourceProvider);
+    var snapshot = snapshotCache.getSnapshot(command.first);
     var snapshotFile = snapshot._snapshotFile;
     var snapshotPath =
         _resourceProvider.pathContext.absolute(snapshotFile.path);
@@ -212,11 +212,11 @@ class _Snapshot {
   void _snapshotCompleted() => _snapshotCompleter.complete();
 }
 
-/// A singleton that keeps track of cached snapshot files. The [dispose]
+/// A class that keeps track of cached snapshot files. The [dispose]
 /// function must be called before process exit to clean up snapshots in the
 /// cache.
 class SnapshotCache {
-  static SnapshotCache _instance;
+  static final _instances = <ResourceProvider, SnapshotCache>{};
 
   final Folder snapshotCache;
   final ResourceProvider _resourceProvider;
@@ -227,10 +227,12 @@ class SnapshotCache {
       : snapshotCache =
             _resourceProvider.createSystemTemp('dartdoc_snapshot_cache_');
 
-  static SnapshotCache get instance => _instance;
-
-  static SnapshotCache createInstance(ResourceProvider resourceProvider) =>
-      _instance ??= SnapshotCache._(resourceProvider);
+  /// Returns a [SnapshotCache] for a given [ResourceProvider], creating one
+  /// only if one doesn't exist yet for the given [ResourceProvider].
+  factory SnapshotCache.instanceFor(ResourceProvider resourceProvider) {
+    return _instances.putIfAbsent(
+        resourceProvider, () => SnapshotCache._(resourceProvider));
+  }
 
   _Snapshot getSnapshot(String toolPath) {
     if (snapshots.containsKey(toolPath)) {
@@ -243,7 +245,7 @@ class SnapshotCache {
   }
 
   void dispose() {
-    _instance = null;
+    _instances.remove(_resourceProvider);
     if (snapshotCache != null && snapshotCache.exists) {
       return snapshotCache.delete();
     }

lib/src/tool_runner.dart

@@ -175,7 +175,7 @@ class ToolRunner {
       // find out where their script was coming from as an absolute path on the
       // filesystem.
       envWithInput['DART_SNAPSHOT_CACHE'] = pathContext.absolute(
-          SnapshotCache.createInstance(resourceProvider).snapshotCache.path);
+          SnapshotCache.instanceFor(resourceProvider).snapshotCache.path);
       if (toolDefinition.setupCommand != null) {
         envWithInput['DART_SETUP_COMMAND'] = toolDefinition.setupCommand[0];
       }

test/tool_runner_test.dart

@@ -95,7 +95,8 @@ echo:
   tearDownAll(() {
     tempDir?.deleteSync(recursive: true);
     tracker?.dispose();
-    SnapshotCache.instance?.dispose();
+    SnapshotCache.instanceFor(pubPackageMetaProvider.resourceProvider)
+        .dispose();
     setupFile = null;
     tempDir = null;
   });