diff --git a/src/main/java/com/google/devtools/build/lib/bazel/repository/cache/RepositoryCache.java b/src/main/java/com/google/devtools/build/lib/bazel/repository/cache/RepositoryCache.java
index 07bc07165521d2..1c350ea7a71053 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/repository/cache/RepositoryCache.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/repository/cache/RepositoryCache.java
@@ -26,12 +26,14 @@
 import com.google.devtools.build.lib.vfs.Path;
 import java.io.IOException;
 import java.io.InputStream;
-import java.io.OutputStream;
 import java.util.UUID;
 import javax.annotation.Nullable;
 
-/** The cache implementation to store download artifacts from external repositories.
- *  TODO(jingwen): Implement file locking for concurrent cache accesses.
+/**
+ * The cache implementation to store download artifacts from external repositories.
+ *
+ * <p>Operations performed by this class are atomic on the file system level under the assumption
+ * that the cache directory is not subject to concurrent file deletion.
  */
 public class RepositoryCache {
 
@@ -134,11 +136,6 @@ boolean hasCanonicalId(String cacheKey, KeyType keyType, String canonicalId) {
         .exists();
   }
 
-  public synchronized Path get(String cacheKey, Path targetPath, KeyType keyType)
-      throws IOException, InterruptedException {
-    return get(cacheKey, targetPath, keyType, null);
-  }
-
   /**
    * Copy or hardlink cached value to a specified directory, if it exists.
    *
@@ -156,12 +153,8 @@ public synchronized Path get(String cacheKey, Path targetPath, KeyType keyType)
    * @throws IOException
    */
   @Nullable
-  public synchronized Path get(
-      String cacheKey, Path targetPath, KeyType keyType, String canonicalId)
+  public Path get(String cacheKey, Path targetPath, KeyType keyType, String canonicalId)
       throws IOException, InterruptedException {
-    if (Thread.interrupted()) {
-      throw new InterruptedException();
-    }
     Preconditions.checkState(isEnabled());
 
     assertKeyIsValid(cacheKey, keyType);
@@ -202,11 +195,6 @@ public synchronized Path get(
     return targetPath;
   }
 
-  public synchronized void put(String cacheKey, Path sourcePath, KeyType keyType)
-      throws IOException, InterruptedException {
-    put(cacheKey, sourcePath, keyType, null);
-  }
-
   /**
    * Copies a value from a specified path into the cache.
    *
@@ -217,13 +205,8 @@ public synchronized void put(String cacheKey, Path sourcePath, KeyType keyType)
    *     restricted cache lookups later.
    * @throws IOException
    */
-  public synchronized void put(
-      String cacheKey, Path sourcePath, KeyType keyType, String canonicalId)
-      throws IOException, InterruptedException {
-    // Check for interrupts while waiting for the monitor of this synchronized method
-    if (Thread.interrupted()) {
-      throw new InterruptedException();
-    }
+  public void put(String cacheKey, Path sourcePath, KeyType keyType, String canonicalId)
+      throws IOException {
     Preconditions.checkState(isEnabled());
 
     assertKeyIsValid(cacheKey, keyType);
@@ -237,19 +220,11 @@ public synchronized void put(
     FileSystemUtils.moveFile(tmpName, cacheValue);
 
     if (!Strings.isNullOrEmpty(canonicalId)) {
-      byte[] canonicalIdBytes = canonicalId.getBytes(UTF_8);
-      String idHash = keyType.newHasher().putBytes(canonicalIdBytes).hash().toString();
-      OutputStream idStream = cacheEntry.getRelative(ID_PREFIX + idHash).getOutputStream();
-      idStream.write(canonicalIdBytes);
-      idStream.close();
+      String idHash = keyType.newHasher().putBytes(canonicalId.getBytes(UTF_8)).hash().toString();
+      FileSystemUtils.touchFile(cacheEntry.getRelative(ID_PREFIX + idHash));
     }
   }
 
-  public synchronized String put(Path sourcePath, KeyType keyType)
-      throws IOException, InterruptedException {
-    return put(sourcePath, keyType, null);
-  }
-
   /**
    * Copies a value from a specified path into the cache, computing the cache key itself.
    *
@@ -260,7 +235,7 @@ public synchronized String put(Path sourcePath, KeyType keyType)
    * @throws IOException
    * @return The key for the cached entry.
    */
-  public synchronized String put(Path sourcePath, KeyType keyType, String canonicalId)
+  public String put(Path sourcePath, KeyType keyType, String canonicalId)
       throws IOException, InterruptedException {
     String cacheKey = getChecksum(keyType, sourcePath);
     put(cacheKey, sourcePath, keyType, canonicalId);
diff --git a/src/test/java/com/google/devtools/build/lib/bazel/repository/cache/RepositoryCacheTest.java b/src/test/java/com/google/devtools/build/lib/bazel/repository/cache/RepositoryCacheTest.java
index 2b0f2e5c142932..e4a9104a0fefee 100644
--- a/src/test/java/com/google/devtools/build/lib/bazel/repository/cache/RepositoryCacheTest.java
+++ b/src/test/java/com/google/devtools/build/lib/bazel/repository/cache/RepositoryCacheTest.java
@@ -74,7 +74,8 @@ public void testNonExistentCacheValue() {
   /** Test that the put method correctly stores the downloaded file into the cache. */
   @Test
   public void testPutCacheValue() throws Exception {
-    repositoryCache.put(downloadedFileSha256, downloadedFile, KeyType.SHA256);
+    repositoryCache.put(
+        downloadedFileSha256, downloadedFile, KeyType.SHA256, /* canonicalId= */ null);
 
     Path cacheEntry = KeyType.SHA256.getCachePath(contentAddressableCachePath).getChild(downloadedFileSha256);
     Path cacheValue = cacheEntry.getChild(RepositoryCache.DEFAULT_CACHE_FILENAME);
@@ -88,7 +89,7 @@ public void testPutCacheValue() throws Exception {
    */
   @Test
   public void testPutCacheValueWithoutHash() throws Exception {
-    String cacheKey = repositoryCache.put(downloadedFile, KeyType.SHA256);
+    String cacheKey = repositoryCache.put(downloadedFile, KeyType.SHA256, /* canonicalId= */ null);
     assertThat(cacheKey).isEqualTo(downloadedFileSha256);
 
     Path cacheEntry =
@@ -105,8 +106,10 @@ public void testPutCacheValueWithoutHash() throws Exception {
    */
   @Test
   public void testPutCacheValueIdempotent() throws Exception {
-    repositoryCache.put(downloadedFileSha256, downloadedFile, KeyType.SHA256);
-    repositoryCache.put(downloadedFileSha256, downloadedFile, KeyType.SHA256);
+    repositoryCache.put(
+        downloadedFileSha256, downloadedFile, KeyType.SHA256, /* canonicalId= */ null);
+    repositoryCache.put(
+        downloadedFileSha256, downloadedFile, KeyType.SHA256, /* canonicalId= */ null);
 
     Path cacheEntry = KeyType.SHA256.getCachePath(contentAddressableCachePath).getChild(downloadedFileSha256);
     Path cacheValue = cacheEntry.getChild(RepositoryCache.DEFAULT_CACHE_FILENAME);
@@ -119,11 +122,14 @@ public void testPutCacheValueIdempotent() throws Exception {
   @Test
   public void testGetCacheValue() throws Exception {
     // Inject file into cache
-    repositoryCache.put(downloadedFileSha256, downloadedFile, KeyType.SHA256);
+    repositoryCache.put(
+        downloadedFileSha256, downloadedFile, KeyType.SHA256, /* canonicalId= */ null);
 
     Path targetDirectory = scratch.dir("/external");
     Path targetPath = targetDirectory.getChild(downloadedFile.getBaseName());
-    Path actualTargetPath = repositoryCache.get(downloadedFileSha256, targetPath, KeyType.SHA256);
+    Path actualTargetPath =
+        repositoryCache.get(
+            downloadedFileSha256, targetPath, KeyType.SHA256, /* canonicalId= */ null);
 
     // Check that the contents are the same.
     assertThat(FileSystemUtils.readContent(downloadedFile, Charset.defaultCharset()))
@@ -138,7 +144,9 @@ public void testGetCacheValue() throws Exception {
   public void testGetNullCacheValue() throws Exception {
     Path targetDirectory = scratch.dir("/external");
     Path targetPath = targetDirectory.getChild(downloadedFile.getBaseName());
-    Path actualTargetPath = repositoryCache.get(downloadedFileSha256, targetPath, KeyType.SHA256);
+    Path actualTargetPath =
+        repositoryCache.get(
+            downloadedFileSha256, targetPath, KeyType.SHA256, /* canonicalId= */ null);
 
     assertThat(actualTargetPath).isNull();
   }
@@ -148,7 +156,7 @@ public void testInvalidSha256Throws() throws Exception {
     String invalidSha = "foo";
     thrown.expect(IOException.class);
     thrown.expectMessage("Invalid key \"foo\" of type SHA-256");
-    repositoryCache.put(invalidSha, downloadedFile, KeyType.SHA256);
+    repositoryCache.put(invalidSha, downloadedFile, KeyType.SHA256, /* canonicalId= */ null);
   }
 
   @Test
@@ -165,7 +173,7 @@ public void testPoisonedCache() throws Exception {
     thrown.expectMessage("does not match expected");
     thrown.expectMessage("Please delete the directory");
 
-    repositoryCache.get(downloadedFileSha256, targetPath, KeyType.SHA256);
+    repositoryCache.get(downloadedFileSha256, targetPath, KeyType.SHA256, /* canonicalId= */ null);
   }
 
   @Test
@@ -215,7 +223,9 @@ public void testCanonicalId() throws Exception {
         repositoryCache.get(downloadedFileSha256, targetPath, KeyType.SHA256, "barid");
     assertThat(lookupOtherId).isNull();
 
-    Path lookupNoId = repositoryCache.get(downloadedFileSha256, targetPath, KeyType.SHA256);
+    Path lookupNoId =
+        repositoryCache.get(
+            downloadedFileSha256, targetPath, KeyType.SHA256, /* canonicalId= */ null);
     assertThat(lookupNoId).isEqualTo(targetPath);
   }
 }