스레드 안전성의 문서화와 검증: Javadoc 표기, 애너테이션, 정적 분석, ArchUnit

synchronized void run() {
    // do something
}

void run() {
    synchronized (this) {
        // do something
    }
}

@NotThreadSafe
public class HttpGet extends HttpRequestBase {

@ThreadSafe
public class DefaultHttpClient extends AbstractHttpClient {

@ThreadSafe
public class SingleClientConnManager implements ClientConnectionManager {

@Contract(threading = ThreadingBehavior.SAFE)
public abstract class CloseableHttpClient implements HttpClient, ModalCloseable {

@Contract(threading = ThreadingBehavior.SAFE_CONDITIONAL)
public class PoolingHttpClientConnectionManager
        implements HttpClientConnectionManager, ConnPoolControl<HttpRoute> {

@Contract(threading = ThreadingBehavior.SAFE)
public class BasicHttpClientConnectionManager implements HttpClientConnectionManager {

package net.benelog;

import net.jcip.annotations.Immutable;

/**
 * {@code @Immutable}로 선언했지만 final이 아닌 필드가 있어서
 * SpotBugs가 JCIP_FIELD_ISNT_FINAL_IN_IMMUTABLE_CLASS로 보고한다.
 */
@Immutable
public class Memo {
	private String content;

	public void setContent(String content) {
		this.content = content;
	}

	public String getContent() {
		return content;
	}
}

plugins {
	java
	id("com.github.spotbugs") version "6.5.11"
}

repositories {
	mavenCentral()
}

dependencies {
	implementation("com.github.stephenc.jcip:jcip-annotations:1.0-1")
}

java {
	toolchain {
		languageVersion.set(JavaLanguageVersion.of(25))
	}
}

spotbugs {
	toolVersion.set("4.10.4")
	ignoreFailures.set(true)
}

tasks.spotbugsMain {
	val report = layout.buildDirectory.file("reports/spotbugs/main.txt")
	reports.create("text") {
		required.set(true)
		outputLocation.set(report)
	}
	doLast {
		println(report.get().asFile.readText())
	}
}

M B JCIP: Memo.content should be final since net.benelog.Memo is marked as Immutable.  In Memo.java

plugins {
	java
	id("net.ltgt.errorprone") version "5.1.1"
}

repositories {
	mavenCentral()
}

dependencies {
	implementation("com.github.stephenc.jcip:jcip-annotations:1.0-1")
	implementation("com.google.code.findbugs:jsr305:3.0.2")
	implementation("com.google.errorprone:error_prone_annotations:2.50.0")
	errorprone("com.google.errorprone:error_prone_core:2.50.0")
}

java {
	toolchain {
		languageVersion.set(JavaLanguageVersion.of(25))
	}
}

package net.benelog;

import javax.annotation.concurrent.GuardedBy;
import javax.annotation.concurrent.ThreadSafe;

/**
 * JSR-305 패키지. Error Prone이 @GuardedBy 위반을 컴파일 오류로 보고한다.
 */
@ThreadSafe
public class JsrCounter {
	@GuardedBy("this")
	private int count;

	public void increment() {
		count++;
	}

	public synchronized int get() {
		return count;
	}
}

JsrCounter.java:15: error: [GuardedBy] This access should be guarded by 'this', which is not currently held
		count++;
		^
    (see https://errorprone.info/bugpattern/GuardedBy)

package net.benelog.report;

import net.jcip.annotations.NotThreadSafe;

@NotThreadSafe
public class ReportFormatter {
	private final StringBuilder buffer = new StringBuilder();

	public String format(String title, String body) {
		buffer.setLength(0);
		return buffer.append(title).append('\n').append(body).toString();
	}
}

package net.benelog.web;

import java.text.SimpleDateFormat;
import java.util.Date;

import net.benelog.report.ReportFormatter;
import net.benelog.report.ReportService;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class ReportController {
	private final ReportService reportService;
	private final ReportFormatter formatter = new ReportFormatter();
	private final SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");

	public ReportController(ReportService reportService) {
		this.reportService = reportService;
	}

	@GetMapping("/reports/{id}")
	public String report(@PathVariable long id) {
		return formatter.format(dateFormat.format(new Date()), reportService.find(id));
	}
}

package net.benelog;

import static com.tngtech.archunit.core.domain.JavaClass.Predicates.assignableTo;
import static com.tngtech.archunit.core.domain.properties.CanBeAnnotated.Predicates.annotatedWith;
import static com.tngtech.archunit.lang.syntax.ArchRuleDefinition.fields;

import java.text.Format;
import java.util.Calendar;

import com.tngtech.archunit.base.DescribedPredicate;
import com.tngtech.archunit.core.domain.JavaClass;
import com.tngtech.archunit.junit.AnalyzeClasses;
import com.tngtech.archunit.junit.ArchTest;
import com.tngtech.archunit.lang.ArchRule;
import net.jcip.annotations.NotThreadSafe;
import org.springframework.web.bind.annotation.RestController;

@AnalyzeClasses(packages = "net.benelog")
class ThreadSafetyArchTest {

	@ArchTest
	static final ArchRule controllers_should_not_hold_not_thread_safe_types =
			fields().that().areDeclaredInClassesThat().areAnnotatedWith(RestController.class)
					.should().notHaveRawType(annotatedWith(NotThreadSafe.class))
					.because("controller는 singleton이라 모든 요청 스레드가 필드를 공유한다");

	private static final DescribedPredicate<JavaClass> KNOWN_NOT_THREAD_SAFE_JDK_TYPES =
			assignableTo(Format.class)
					.or(assignableTo(Calendar.class))
					.or(assignableTo(StringBuilder.class))
					.as("JDK의 스레드 안전하지 않은 타입(Format, Calendar, StringBuilder)");

	@ArchTest
	static final ArchRule controllers_should_not_hold_known_not_thread_safe_jdk_types =
			fields().that().areDeclaredInClassesThat().areAnnotatedWith(RestController.class)
					.should().notHaveRawType(KNOWN_NOT_THREAD_SAFE_JDK_TYPES)
					.because("JDK 클래스에는 스레드 안전성 애너테이션이 없으므로 목록으로 막는다");
}

Architecture Violation [Priority: MEDIUM] - Rule 'fields that are declared in classes that are annotated with @RestController should not have raw type annotated with @NotThreadSafe, because controller는 singleton이라 모든 요청 스레드가 필드를 공유한다' was violated (1 times):
Field <net.benelog.web.ReportController.formatter> has raw type annotated with @NotThreadSafe in (ReportController.java:0)

Architecture Violation [Priority: MEDIUM] - Rule 'fields that are declared in classes that are annotated with @RestController should not have raw type JDK의 스레드 안전하지 않은 타입(Format, Calendar, StringBuilder), because JDK 클래스에는 스레드 안전성 애너테이션이 없으므로 목록으로 막는다' was violated (1 times):
Field <net.benelog.web.ReportController.dateFormat> has raw type JDK의 스레드 안전하지 않은 타입(Format, Calendar, StringBuilder) in (ReportController.java:0)