WIP

Author: fmeum

src/main/java/com/google/devtools/build/lib/skyframe/RewoundActionSynchronizer.java

@@ -0,0 +1,60 @@
+package com.google.devtools.build.lib.skyframe;
+
+import com.google.devtools.build.lib.actions.Action;
+import com.google.devtools.build.lib.actions.Artifact;
+import com.google.devtools.build.lib.profiler.SilentCloseable;
+import com.google.devtools.build.lib.vfs.OutputService.ActionFileSystemType;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+import javax.annotation.Nullable;
+
+interface RewoundActionSynchronizer {
+  SilentCloseable lockForRewoundActionBeforePreparation(Action action) throws InterruptedException;
+
+  SilentCloseable lockForAnyActionBeforeExecution(Action action) throws InterruptedException;
+
+  RewoundActionSynchronizer NOOP =
+      new RewoundActionSynchronizer() {
+        @Override
+        public SilentCloseable lockForRewoundActionBeforePreparation(Action action) {
+          return () -> {};
+        }
+
+        @Override
+        public SilentCloseable lockForAnyActionBeforeExecution(Action action) {
+          return () -> {};
+        }
+      };
+
+  static RewoundActionSynchronizer create(
+      boolean rewindingEnabled, ActionFileSystemType actionFileSystemType) {
+    if (rewindingEnabled && actionFileSystemType.shouldDoEagerActionPrep()) {
+      return new BazelRewoundActionSynchronizer();
+    } else {
+      return NOOP;
+    }
+  }
+
+  final class BazelRewoundActionSynchronizer implements RewoundActionSynchronizer {
+    @Nullable private volatile ReentrantReadWriteLock coarseLock = new ReentrantReadWriteLock();
+    @Nullable private volatile ConcurrentHashMap<Artifact, ReentrantReadWriteLock> fineLocks = null;
+
+    private BazelRewoundActionSynchronizer() {}
+
+    @Override
+    public SilentCloseable lockForRewoundActionBeforePreparation(Action action)
+        throws InterruptedException {
+      if (coarseLock != null) {
+        coarseLock.writeLock().lockInterruptibly();
+        coarseLock = null;
+      }
+      return null;
+    }
+
+    @Override
+    public SilentCloseable lockForAnyActionBeforeExecution(Action action)
+        throws InterruptedException {
+      return null;
+    }
+  }
+}