webview: avoid reentrant locking problems.

The metric for re-initializing WebView showed that this is indeed what
a small number of apps are doing in a very small proportion of cases.
While we don't make any guarantees that this will work and the app might
just crash in other ways, there's no benefit to it failing in
AwDataDirLock in particular, so it seems preferable to just tolerate it
here.

So, just allow init to continue if we're already holding the lock, and
if we already opened the file but didn't acquire the lock, reuse the
already open file to try again, so that we don't end up racing with the
finalizer of the old file object and potentially cause more problems.

This should prevent us from hitting the OverlappingFileLockException in
this code, though apps that are in this state may simply crash somewhere
else in initialization later.

Fixed: 1054774
Change-Id: I8aade5278a7fad10433a97068e36fbf63196e67a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2498109
Auto-Submit: Richard Coles <torne@chromium.org>
Commit-Queue: Nate Fischer <ntfschr@chromium.org>
Reviewed-by: Nate Fischer <ntfschr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820970}

android_webview/java/src/org/chromium/android_webview/AwDataDirLock.java

@@ -17,8 +17,6 @@ import org.chromium.base.PathUtils;
 import org.chromium.base.StrictModeContext;
 import org.chromium.base.metrics.RecordHistogram;
 import org.chromium.base.metrics.ScopedSysTraceEvent;
-import org.chromium.components.version_info.Channel;
-import org.chromium.components.version_info.VersionConstants;
 
 import java.io.File;
 import java.io.IOException;
@@ -46,25 +44,19 @@ abstract class AwDataDirLock {
                 StrictModeContext ignored = StrictModeContext.allowDiskWrites()) {
             if (sExclusiveFileLock != null) {
                 // We have already called lock() and successfully acquired the lock in this process.
-                // This shouldn't happen, but may be the result of an app catching an exception
-                // thrown during initialization and discarding it, causing us to later attempt to
-                // initialize WebView again. By continuing, we are racing with the file being closed
-                // by the finalizer (releasing the lock), and so we may or may not crash with
-                // OverlappingFileLockException. Ideally we'd explicitly crash here but we don't
-                // want to make this problem worse until we fully understand it, so on stable we
-                // just log and then let execution continue; the app will either be lucky or not
-                // with roughly the same chance/conditions as before these checks were implemented.
-                throwIfNotStableChannel("Data directory already locked by current process - "
-                        + "https://crbug.com/1054774");
-            } else if (sLockFile != null) {
-                // We have already called lock() but didn't succeed in getting the lock. As above
-                // this shouldn't happen, but this won't lead to OverlappingFileLockException.
-                // Again, we just log and then let execution continue on stable; if the app fails to
-                // acquire the lock again we'll crash from that anyway.
-                throwIfNotStableChannel("Previous data directory lock attempt in current process - "
-                        + "https://crbug.com/1054744");
+                // This shouldn't happen, but is likely to be the result of an app catching an
+                // exception thrown during initialization and discarding it, causing us to later
+                // attempt to initialize WebView again. There's no real advantage to failing the
+                // locking code when this happens; we may as well count this as the lock being
+                // acquired and let init continue (though the app may experience other problems
+                // later).
+                return;
             }
 
+            // If we already called lock() but didn't succeed in getting the lock, it's possible the
+            // app caught the exception and tried again later. As above, there's no real advantage
+            // to failing here, so only open the lock file if we didn't already open it before.
+            if (sLockFile == null) {
                 String dataPath = PathUtils.getDataDirectory();
                 File lockFile = new File(dataPath, EXCLUSIVE_LOCK_FILE);
 
@@ -72,14 +64,18 @@ abstract class AwDataDirLock {
                     // Note that the file is kept open intentionally.
                     sLockFile = new RandomAccessFile(lockFile, "rw");
                 } catch (IOException e) {
-                // Failing to create the lock file is always fatal; even if multiple processes are
-                // using the same data directory we should always be able to access the file itself.
+                    // Failing to create the lock file is always fatal; even if multiple processes
+                    // are using the same data directory we should always be able to access the file
+                    // itself.
                     throw new RuntimeException("Failed to create lock file " + lockFile, e);
                 }
+            }
 
             // Android versions before 11 have edge cases where a new instance of an app process can
-            // be started while an existing one is still in the process of being killed. Retry
-            // the lock a few times to give the old process time to fully go away.
+            // be started while an existing one is still in the process of being killed. This can
+            // still happen on Android 11+ because the platform has a timeout for waiting, but it's
+            // much less likely. Retry the lock a few times to give the old process time to fully go
+            // away.
             for (int attempts = 1; attempts <= LOCK_RETRIES; ++attempts) {
                 try {
                     sExclusiveFileLock = sLockFile.getChannel().tryLock();
@@ -178,12 +174,4 @@ abstract class AwDataDirLock {
         }
         return error.toString();
     }
-
-    private static void throwIfNotStableChannel(String error) {
-        if (VersionConstants.CHANNEL == Channel.STABLE) {
-            Log.e(TAG, error);
-        } else {
-            throw new RuntimeException(error);
-        }
-    }
 }