Replace synchronized blocks and methods with locks

This commit replaces synchronized blocks and methods
that are used frequently or that guard blocking I/O
operations with locks. This is required to prevent
virtual threads pinning, as explained in JEP 444 [1].

Note that synchronized blocks and methods that are used
infrequently (like AutomaticJobRegistrar#start/stop) or
that guard in-memory operations were not replaced as this
is not required, see JEP 444 [1].

Resolves to #4399

---
[1]: https://openjdk.org/jeps/444

spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/JdbcExecutionContextDao.java

@@ -30,6 +30,8 @@ import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 
 import org.springframework.batch.core.JobExecution;
 import org.springframework.batch.core.StepExecution;
@@ -112,6 +114,8 @@ public class JdbcExecutionContextDao extends AbstractJdbcBatchMetadataDao implem
 
 	private ExecutionContextSerializer serializer = new DefaultExecutionContextSerializer();
 
+	private final Lock lock = new ReentrantLock();
+
 	/**
 	 * Setter for {@link Serializer} implementation
 	 * @param serializer {@link ExecutionContextSerializer} instance to use.
@@ -191,7 +195,8 @@ public class JdbcExecutionContextDao extends AbstractJdbcBatchMetadataDao implem
 	public void updateExecutionContext(final StepExecution stepExecution) {
 		// Attempt to prevent concurrent modification errors by blocking here if
 		// someone is already trying to do it.
-		synchronized (stepExecution) {
+		this.lock.lock();
+		try {
 			Long executionId = stepExecution.getId();
 			ExecutionContext executionContext = stepExecution.getExecutionContext();
 			Assert.notNull(executionId, "ExecutionId must not be null.");
@@ -201,6 +206,9 @@ public class JdbcExecutionContextDao extends AbstractJdbcBatchMetadataDao implem
 
 			persistSerializedContext(executionId, serializedContext, UPDATE_STEP_EXECUTION_CONTEXT);
 		}
+		finally {
+			this.lock.unlock();
+		}
 	}
 
 	@Override

spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/JdbcJobExecutionDao.java

@@ -26,6 +26,8 @@ import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -158,6 +160,8 @@ public class JdbcJobExecutionDao extends AbstractJdbcBatchMetadataDao implements
 
 	private ConfigurableConversionService conversionService;
 
+	private final Lock lock = new ReentrantLock();
+
 	public JdbcJobExecutionDao() {
 		DefaultConversionService conversionService = new DefaultConversionService();
 		conversionService.addConverter(new DateToStringConverter());
@@ -278,7 +282,8 @@ public class JdbcJobExecutionDao extends AbstractJdbcBatchMetadataDao implements
 		Assert.notNull(jobExecution.getVersion(),
 				"JobExecution version cannot be null. JobExecution must be saved before it can be updated");
 
-		synchronized (jobExecution) {
+		this.lock.lock();
+		try {
 			Integer version = jobExecution.getVersion() + 1;
 
 			String exitDescription = jobExecution.getExitStatus().getExitDescription();
@@ -323,6 +328,9 @@ public class JdbcJobExecutionDao extends AbstractJdbcBatchMetadataDao implements
 
 			jobExecution.incrementVersion();
 		}
+		finally {
+			this.lock.unlock();
+		}
 	}
 
 	@Nullable

spring-batch-core/src/main/java/org/springframework/batch/core/repository/dao/JdbcStepExecutionDao.java

@@ -26,6 +26,8 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.Iterator;
 import java.util.List;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -119,6 +121,8 @@ public class JdbcStepExecutionDao extends AbstractJdbcBatchMetadataDao implement
 
 	private DataFieldMaxValueIncrementer stepExecutionIncrementer;
 
+	private final Lock lock = new ReentrantLock();
+
 	/**
 	 * Public setter for the exit message length in database. Do not set this if you
 	 * haven't modified the schema.
@@ -256,7 +260,8 @@ public class JdbcStepExecutionDao extends AbstractJdbcBatchMetadataDao implement
 
 		// Attempt to prevent concurrent modification errors by blocking here if
 		// someone is already trying to do it.
-		synchronized (stepExecution) {
+		this.lock.lock();
+		try {
 
 			Integer version = stepExecution.getVersion() + 1;
 			Timestamp startTime = stepExecution.getStartTime() == null ? null
@@ -289,6 +294,9 @@ public class JdbcStepExecutionDao extends AbstractJdbcBatchMetadataDao implement
 			stepExecution.incrementVersion();
 
 		}
+		finally {
+			this.lock.unlock();
+		}
 	}
 
 	/**