feat: ch12 정리

Author: Eom-Ti

src/main/java/com/example/concurrency/JavaOneToOneThreadTest.java

@@ -0,0 +1,116 @@
+package com.example.concurrency;
+
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+
+public class JavaOneToOneThreadTest {
+
+    public static void main(String[] args) throws InterruptedException {
+        long pid = ProcessHandle.current().pid();
+        String osName = System.getProperty("os.name").toLowerCase();
+
+        System.out.println("PID: " + pid);
+        System.out.println();
+
+        System.out.println("=== 초기 상태 ===");
+        int initialOsThreads = getThreadCount(pid, osName);
+        int initialJavaThreads = Thread.activeCount();
+        System.out.println("Java Thread 수: " + initialJavaThreads);
+        System.out.println("OS Thread 수: " + initialOsThreads);
+        System.out.println();
+
+        System.out.println("=== 5개 Thread 생성 테스트 ===");
+        for (int i = 1; i <= 5; i++) {
+            final int id = i;
+            new Thread(() -> {
+                System.out.println("Thread-" + id + " 생성");
+                try {
+                    while (true) Thread.sleep(1000);
+                } catch (InterruptedException e) {
+                    Thread.currentThread().interrupt();
+                }
+            }).start();
+            Thread.sleep(200);
+        }
+
+        Thread.sleep(2000);
+
+        System.out.println();
+        System.out.println("=== 테스트 완료 후 ===");
+        int finalOsThreads = getThreadCount(pid, osName);
+        int finalJavaThreads = Thread.activeCount();
+        System.out.println("Java Thread 수: " + finalJavaThreads);
+        System.out.println("OS Thread 수: " + finalOsThreads);
+        System.out.println();
+
+        int javaIncrease = finalJavaThreads - initialJavaThreads;
+        int osIncrease = finalOsThreads - initialOsThreads;
+
+        System.out.println("=== 증가량 분석 ===");
+        System.out.println("생성한 Thread: 5개");
+        System.out.println("Main Thread: 1개 (이미 실행 중)");
+        System.out.println("Java Thread 증가: " + javaIncrease + "개");
+        System.out.println("OS Thread 증가: " + osIncrease + "개");
+        System.out.println();
+
+        System.out.println("=== 1:1 매핑 검증 ===");
+        printMappingResult(javaIncrease, osIncrease);
+
+        Thread.sleep(30000);
+    }
+
+    private static void printMappingResult(int javaIncrease, int osIncrease) {
+        System.out.println("Java Thread 증가: " + javaIncrease);
+        System.out.println("OS Thread 증가:   " + osIncrease);
+        System.out.println();
+
+        if (javaIncrease == osIncrease) {
+            System.out.println("결과: PERFECT 1:1 매핑!");
+            System.out.println("┌─ Java Thread ─┐    ┌─ OS Thread ─┐");
+            System.out.println("│     " + javaIncrease + "개      │ ←→ │    " + osIncrease + "개     │");
+            System.out.println("└───────────────┘    └─────────────┘");
+        } else {
+            System.out.println("결과: 차이 발생 (" + (osIncrease - javaIncrease) + "개)");
+            System.out.println("┌─ Java Thread ─┐    ┌─ OS Thread ─┐");
+            System.out.println("│     " + javaIncrease + "개      │ ≠  │    " + osIncrease + "개     │");
+            System.out.println("└───────────────┘    └─────────────┘");
+            System.out.println("차이 원인: JVM 내부 Thread 추가 생성");
+        }
+    }
+
+    private static int getThreadCount(long pid, String osName) {
+        try {
+            String command;
+            if (osName.contains("windows")) {
+                command = "wmic process where \"ProcessId=" + pid + "\" get ThreadCount /format:value";
+            } else if (osName.contains("mac")) {
+                command = "ps -M " + pid + " | wc -l";
+            } else {
+                command = "ps -T -p " + pid + " | wc -l";
+            }
+
+            Process process = Runtime.getRuntime().exec(command);
+            BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
+
+            String line;
+            while ((line = reader.readLine()) != null) {
+                if (osName.contains("windows")) {
+                    if (line.startsWith("ThreadCount=")) {
+                        return Integer.parseInt(line.split("=")[1].trim());
+                    }
+                } else {
+                    try {
+                        int count = Integer.parseInt(line.trim());
+                        if (count > 0) return count - 1;
+                    } catch (NumberFormatException ignored) {}
+                }
+            }
+            reader.close();
+
+        } catch (Exception e) {
+            System.out.println("명령어 실행 오류: " + e.getMessage());
+        }
+
+        return -1;
+    }
+}