Execute blocking tx functions in caller thread

This commit brings back blocking retry logic that performs retries in
the caller thread and uses `Thread#sleep()` between retries. It is
needed because blocking tx functions can't run in event loop as they
perform blocking operations. Event loop thread can deadlock waiting for
itself to read from the network. Previously code used a "hack" and
executed given function in `ForkJoinPool.commonPool()`.

Also added couple tests for retry logic and async transaction functions.

Author: lutovich

driver/src/main/java/org/neo4j/driver/internal/NetworkSession.java

@@ -289,32 +289,34 @@ CompletionStage<Boolean> currentConnectionIsOpen()
 
     private <T> T transaction( AccessMode mode, TransactionWork<T> work )
     {
-        return getBlocking( transactionAsync( mode, tx ->
+        // use different code path compared to async so that work is executed in the caller thread
+        // caller thread will also be the one who sleeps between retries;
+        // it is unsafe to execute retries in the event loop threads because this can cause a deadlock
+        // event loop thread will bock and wait for itself to read some data
+        return retryLogic.retry( () ->
         {
-            try
-            {
-                // todo: given lambda can't be executed in even loop thread because it deadlocks
-                // todo: event loop executes a blocking operation and waits for itself to read from the network
-                // todo: this is most likely what happens...
-
-                // todo: use of supplyAsync is a hack and it makes blocking API very different from 1.4
-                // todo: because we now execute function in FJP.commonPool()
-
-                // todo: bring back blocking retries with sleeps and etc. so that we execute TxWork in caller thread
-                return CompletableFuture.supplyAsync( () -> work.execute( tx ) );
-//                T result = work.execute( tx );
-//                return completedFuture( result );
-            }
-            catch ( Throwable error )
+            try ( Transaction tx = getBlocking( beginTransactionAsync( mode ) ) )
             {
-                return failedFuture( error );
+                try
+                {
+                    T result = work.execute( tx );
+                    tx.success();
+                    return result;
+                }
+                catch ( Throwable t )
+                {
+                    // mark transaction for failure if the given unit of work threw exception
+                    // this will override any success marks that were made by the unit of work
+                    tx.failure();
+                    throw t;
+                }
             }
-        } ) );
+        } );
     }
 
     private <T> CompletionStage<T> transactionAsync( AccessMode mode, TransactionWork<CompletionStage<T>> work )
     {
-        return retryLogic.retry( () ->
+        return retryLogic.retryAsync( () ->
         {
             CompletableFuture<T> resultFuture = new CompletableFuture<>();
             CompletionStage<ExplicitTransaction> txFuture = beginTransactionAsync( mode );

driver/src/main/java/org/neo4j/driver/internal/retry/ExponentialBackoffRetryLogic.java

@@ -80,7 +80,48 @@ public ExponentialBackoffRetryLogic( RetrySettings settings, EventExecutorGroup
     }
 
     @Override
-    public <T> CompletionStage<T> retry( Supplier<CompletionStage<T>> work )
+    public <T> T retry( Supplier<T> work )
+    {
+        List<Throwable> errors = null;
+        long startTime = -1;
+        long nextDelayMs = initialRetryDelayMs;
+
+        while ( true )
+        {
+            try
+            {
+                return work.get();
+            }
+            catch ( Throwable error )
+            {
+                if ( canRetryOn( error ) )
+                {
+                    long currentTime = clock.millis();
+                    if ( startTime == -1 )
+                    {
+                        startTime = currentTime;
+                    }
+
+                    long elapsedTime = currentTime - startTime;
+                    if ( elapsedTime < maxRetryTimeMs )
+                    {
+                        long delayWithJitterMs = computeDelayWithJitter( nextDelayMs );
+                        log.warn( "Transaction failed and will be retried in " + delayWithJitterMs + "ms", error );
+
+                        sleep( delayWithJitterMs );
+                        nextDelayMs = (long) (nextDelayMs * multiplier);
+                        errors = recordError( error, errors );
+                        continue;
+                    }
+                }
+                addSuppressed( error, errors );
+                throw error;
+            }
+        }
+    }
+
+    @Override
+    public <T> CompletionStage<T> retryAsync( Supplier<CompletionStage<T>> work )
     {
         CompletableFuture<T> resultFuture = new CompletableFuture<>();
         executeWorkInEventLoop( resultFuture, work );
@@ -109,7 +150,7 @@ private <T> void retryWorkInEventLoop( CompletableFuture<T> resultFuture, Suppli
         EventExecutor eventExecutor = eventExecutorGroup.next();
 
         long delayWithJitterMs = computeDelayWithJitter( delayMs );
-        log.warn( "Transaction failed and is scheduled to retry in " + delayWithJitterMs + "ms", error );
+        log.warn( "Async transaction failed and is scheduled to retry in " + delayWithJitterMs + "ms", error );
 
         eventExecutor.schedule( () ->
         {
@@ -185,6 +226,19 @@ private long computeDelayWithJitter( long delayMs )
         return ThreadLocalRandom.current().nextLong( min, max + 1 );
     }
 
+    private void sleep( long delayMs )
+    {
+        try
+        {
+            clock.sleep( delayMs );
+        }
+        catch ( InterruptedException e )
+        {
+            Thread.currentThread().interrupt();
+            throw new IllegalStateException( "Retries interrupted", e );
+        }
+    }
+
     private void verifyAfterConstruction()
     {
         if ( maxRetryTimeMs < 0 )

driver/src/main/java/org/neo4j/driver/internal/retry/RetryLogic.java

@@ -24,5 +24,7 @@
 
 public interface RetryLogic
 {
-    <T> CompletionStage<T> retry( Supplier<CompletionStage<T>> work );
+    <T> T retry( Supplier<T> work );
+
+    <T> CompletionStage<T> retryAsync( Supplier<CompletionStage<T>> work );
 }