Cache PerBuildSyscallCache if concurrency level is unchanged.

--
MOS_MIGRATED_REVID=138893829

3 files changed, 26 insertions, 3 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/PerBuildSyscallCache.java b/src/main/java/com/google/devtools/build/lib/skyframe/PerBuildSyscallCache.java
index ebb0618ae9..646d6093dd 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/PerBuildSyscallCache.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/PerBuildSyscallCache.java
@@ -22,7 +22,6 @@ import com.google.devtools.build.lib.vfs.FileStatus;
 import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.lib.vfs.Symlinks;
 import com.google.devtools.build.lib.vfs.UnixGlob;
-
 import java.io.IOException;
 import java.util.Collection;
 
@@ -110,6 +109,11 @@ public class PerBuildSyscallCache implements UnixGlob.FilesystemCalls {
     return (status == NO_STATUS) ? null : status;
   }
 
+  public void clear() {
+    statCache.invalidateAll();
+    readdirCache.invalidateAll();
+  }
+
   // This is used because the cache implementations don't allow null.
   private static final class FakeFileStatus implements FileStatus {
     @Override
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/SequencedSkyframeExecutor.java b/src/main/java/com/google/devtools/build/lib/skyframe/SequencedSkyframeExecutor.java
index 40e8a5d14f..f64ed90fae 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/SequencedSkyframeExecutor.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/SequencedSkyframeExecutor.java
@@ -543,7 +543,7 @@ public final class SequencedSkyframeExecutor extends SkyframeExecutor {
     } else {
       diff = getDiff(tsgm, modifiedFileSet.modifiedSourceFiles(), pathEntry);
     }
-    syscalls.set(newPerBuildSyscallCache(/*concurrencyLevel=*/42));
+    syscalls.set(getPerBuildSyscallCache(/*concurrencyLevel=*/ 42));
     recordingDiffer.invalidate(diff.changedKeysWithoutNewValues());
     recordingDiffer.inject(diff.changedKeysWithNewValues());
     // Blaze invalidates transient errors on every build.
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeExecutor.java b/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeExecutor.java
index 6e7d591afd..825fc78a60 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeExecutor.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeExecutor.java
@@ -279,6 +279,9 @@ public abstract class SkyframeExecutor implements WalkableGraphFactory {
   
   private final List<BuildFileName> buildFilesByPriority;
 
+  private PerBuildSyscallCache perBuildSyscallCache;
+  private int lastConcurrencyLevel = -1;
+
   private static final Logger LOG = Logger.getLogger(SkyframeExecutor.class.getName());
 
   protected SkyframeExecutor(
@@ -462,6 +465,22 @@ public abstract class SkyframeExecutor implements WalkableGraphFactory {
     return PerBuildSyscallCache.newBuilder().setConcurrencyLevel(concurrencyLevel).build();
   }
 
+  /**
+   * Gets a (possibly cached) syscalls cache, re-initialized each build.
+   *
+   * <p>We cache the syscalls cache if possible because construction of the cache is surprisingly
+   * expensive, and is on the critical path of null builds.
+   */
+  protected final PerBuildSyscallCache getPerBuildSyscallCache(int concurrencyLevel) {
+    if (lastConcurrencyLevel == concurrencyLevel) {
+      perBuildSyscallCache.clear();
+      return perBuildSyscallCache;
+    }
+    lastConcurrencyLevel = concurrencyLevel;
+    perBuildSyscallCache = newPerBuildSyscallCache(concurrencyLevel);
+    return perBuildSyscallCache;
+  }
+
  @ThreadCompatible
   public void setActive(boolean active) {
     this.active = active;
@@ -934,7 +953,7 @@ public abstract class SkyframeExecutor implements WalkableGraphFactory {
     setupDefaultPackage(defaultsPackageContents);
     setPackageLocator(pkgLocator);
 
-    syscalls.set(newPerBuildSyscallCache(packageCacheOptions.globbingThreads));
+    syscalls.set(getPerBuildSyscallCache(packageCacheOptions.globbingThreads));
     this.pkgFactory.setGlobbingThreads(packageCacheOptions.globbingThreads);
     this.pkgFactory.setMaxDirectoriesToEagerlyVisitInGlobbing(
         packageCacheOptions.maxDirectoriesToEagerlyVisitInGlobbing);