LocatableResolver { @Nonnull public CompletableFuture<Void> exclusiveLock() { return updateAndCommitResolverState(StateMutation.EXCLUSIVE_LOCK); } protected  LocatableResolver(@Nonnull FDBDatabase database,
                                @Nullable KeySpacePath path,
                                @Nullable CompletableFuture<ResolvedKeySpacePath> resolvedPath); ScopedValue<T> wrap(T value); @Nonnull FDBDatabase getDatabase(); @Nonnull CompletableFuture<Long> resolve(@Nonnull String name); @Nonnull CompletableFuture<Long> resolve(@Nullable FDBStoreTimer timer, @Nonnull String name); @API(API.Status.UNSTABLE) @Nonnull CompletableFuture<Long> resolve(@Nonnull FDBRecordContext context, @Nonnull String name); @Nonnull CompletableFuture<Long> resolve(@Nonnull String name,
                                           @Nonnull ResolverCreateHooks hooks); @Nonnull CompletableFuture<Long> resolve(@Nullable FDBStoreTimer timer,
                                           @Nonnull String name,
                                           @Nonnull ResolverCreateHooks hooks); @API(API.Status.UNSTABLE) @Nonnull CompletableFuture<Long> resolve(@Nonnull FDBRecordContext context,
                                           @Nonnull String name,
                                           @Nonnull ResolverCreateHooks hooks); @Nonnull CompletableFuture<ResolverResult> resolveWithMetadata(@Nonnull String name,
                                                                 @Nonnull ResolverCreateHooks hooks); @Nonnull CompletableFuture<ResolverResult> resolveWithMetadata(@Nullable FDBStoreTimer timer,
                                                                 @Nonnull String name,
                                                                 @Nonnull ResolverCreateHooks hooks); @API(API.Status.UNSTABLE) @Nonnull CompletableFuture<ResolverResult> resolveWithMetadata(@Nonnull FDBRecordContext context, @Nonnull String name, @Nonnull ResolverCreateHooks hooks); @Nonnull CompletableFuture<ResolverResult> mustResolveWithMetadata(@Nonnull FDBRecordContext context, @Nonnull String name); CompletableFuture<Long> mustResolve(@Nonnull FDBRecordContext context, @Nonnull String name); @Nonnull CompletableFuture<String> reverseLookup(@Nullable FDBStoreTimer timer, @Nonnull Long value); @Nonnull CompletableFuture<Void> exclusiveLock(); @Nonnull CompletableFuture<Void> enableWriteLock(); @Nonnull CompletableFuture<Void> disableWriteLock(); @Nonnull CompletableFuture<Void> retireLayer(); @Nonnull CompletableFuture<Void> incrementVersion(); @Nonnull CompletableFuture<Integer> getVersion(@Nullable FDBStoreTimer timer); @Nonnull CompletableFuture<Boolean> retired(@Nullable FDBStoreTimer timer); @Nonnull CompletableFuture<Boolean> retiredSkipCache(@Nonnull FDBRecordContext context); @Nonnull CompletableFuture<Void> updateMetadataAndVersion(@Nonnull final String key,
                                                            @Nullable final byte[] metadata); @VisibleForTesting final CompletableFuture<Void> setMapping(FDBRecordContext context, String key, Long value); @VisibleForTesting abstract CompletableFuture<Void> setWindow(long count); @Nonnull @API(API.Status.DEPRECATED) @Deprecated Subspace getMappingSubspace(); @Nonnull abstract CompletableFuture<Subspace> getMappingSubspaceAsync(); @Nonnull @API(API.Status.DEPRECATED) @Deprecated Subspace getBaseSubspace(); @Nonnull abstract CompletableFuture<Subspace> getBaseSubspaceAsync(); @Nonnull abstract ResolverResult deserializeValue(byte[] value); @Override String toString(); @Override boolean equals(Object obj); @Override int hashCode();  }
@Test public void testExclusiveLock() { database.setResolverStateRefreshTimeMillis(100); globalScope.exclusiveLock().join(); assertLocked(database, globalScope); try { globalScope.exclusiveLock().join(); fail("lock already enabled, should fail"); } catch (CompletionException ex) { assertThat("we get the correct cause", ex.getCause(), allOf( instanceOf(LocatableResolverLockedException.class), hasMessageContaining("resolver must be unlocked to get exclusive lock") )); } }
@Test public void testExclusiveLockParallel() { List<CompletableFuture<Void>> parallelGets = new ArrayList<>(); AtomicInteger lockGetCount = new AtomicInteger(); for (int i = 0; i < 20; i++) { parallelGets.add(globalScope.exclusiveLock().handle((ignore, ex) -> { if (ex == null) { lockGetCount.incrementAndGet(); return null; } else if (ex instanceof LocatableResolverLockedException || (ex instanceof CompletionException && ex.getCause() instanceof LocatableResolverLockedException)) { return null; } throw new AssertionError("unexpected error", ex); })); } CompletableFuture.allOf(parallelGets.toArray(new CompletableFuture<?>[0])).join(); assertThat("only one exclusiveLock succeeds", lockGetCount.get(), is(1)); assertLocked(database, globalScope); }