Remove unnecessary synchronization

- on AtomicBoolean in SpringApplicationBuilder
- on SimpleFormatter
- in a private method in FileSystemWatcher which is always called in a
  synchronized block
- Replaced synchronized guarded HashMap with ConcurrentHashMap

spring-boot-project/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/filewatch/FileSystemWatcher.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2022 the original author or authors.
+ * Copyright 2012-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -158,9 +158,7 @@ public class FileSystemWatcher {
 	}
 
 	private void checkNotStarted() {
-		synchronized (this.monitor) {
-			Assert.state(this.watchThread == null, "FileSystemWatcher already started");
-		}
+		Assert.state(this.watchThread == null, "FileSystemWatcher already started");
 	}
 
 	/**

spring-boot-project/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/restart/Restarter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2022 the original author or authors.
+ * Copyright 2012-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,7 +22,6 @@ import java.lang.reflect.Field;
 import java.net.URL;
 import java.util.Arrays;
 import java.util.Collection;
-import java.util.HashMap;
 import java.util.LinkedHashSet;
 import java.util.LinkedList;
 import java.util.List;
@@ -30,6 +29,7 @@ import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.BlockingDeque;
 import java.util.concurrent.Callable;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.LinkedBlockingDeque;
 import java.util.concurrent.ThreadFactory;
@@ -92,7 +92,7 @@ public class Restarter {
 
 	private final ClassLoaderFiles classLoaderFiles = new ClassLoaderFiles();
 
-	private final Map<String, Object> attributes = new HashMap<>();
+	private final Map<String, Object> attributes = new ConcurrentHashMap<>();
 
 	private final BlockingDeque<LeakSafeThread> leakSafeThreads = new LinkedBlockingDeque<>();
 
@@ -440,18 +440,11 @@ public class Restarter {
 	}
 
 	public Object getOrAddAttribute(String name, final ObjectFactory<?> objectFactory) {
-		synchronized (this.attributes) {
-			if (!this.attributes.containsKey(name)) {
-				this.attributes.put(name, objectFactory.getObject());
-			}
-			return this.attributes.get(name);
-		}
+		return this.attributes.computeIfAbsent(name, (ignore) -> objectFactory.getObject());
 	}
 
 	public Object removeAttribute(String name) {
-		synchronized (this.attributes) {
-			return this.attributes.remove(name);
-		}
+		return this.attributes.remove(name);
 	}
 
 	/**

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/builder/SpringApplicationBuilder.java

@@ -76,7 +76,7 @@ public class SpringApplicationBuilder {
 
 	private final SpringApplication application;
 
-	private ConfigurableApplicationContext context;
+	private volatile ConfigurableApplicationContext context;
 
 	private SpringApplicationBuilder parent;
 
@@ -145,10 +145,8 @@ public class SpringApplicationBuilder {
 		}
 		configureAsChildIfNecessary(args);
 		if (this.running.compareAndSet(false, true)) {
-			synchronized (this.running) {
-				// If not already running copy the sources over and then run.
-				this.context = build().run(args);
-			}
+			// If not already running copy the sources over and then run.
+			this.context = build().run(args);
 		}
 		return this.context;
 	}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/java/SimpleFormatter.java

@@ -38,17 +38,15 @@ public class SimpleFormatter extends Formatter {
 
 	private final String pid = getOrUseDefault(LoggingSystemProperty.PID.getEnvironmentVariableName(), "????");
 
-	private final Date date = new Date();
-
 	@Override
-	public synchronized String format(LogRecord record) {
-		this.date.setTime(record.getMillis());
+	public String format(LogRecord record) {
+		Date date = new Date(record.getMillis());
 		String source = record.getLoggerName();
 		String message = formatMessage(record);
 		String throwable = getThrowable(record);
 		String thread = getThreadName();
-		return String.format(this.format, this.date, source, record.getLoggerName(),
-				record.getLevel().getLocalizedName(), message, throwable, thread, this.pid);
+		return String.format(this.format, date, source, record.getLoggerName(), record.getLevel().getLocalizedName(),
+				message, throwable, thread, this.pid);
 	}
 
 	private String getThrowable(LogRecord record) {