GeezerVison is showing github.com — [add] add examples of gc · yyfullstack/java-learning@0ebc64a
File tree
Expand file treeCollapse file tree
Open diff view settings
java-jvm/src/main/java/com/brianway/learning/java/jvm/gc
Expand file treeCollapse file tree
Open diff view settings
Collapse file
Copy file name to clipboard +58Lines changed: 58 additions & 0 deletions | Original file line number | Diff line number | Diff line change |
|---|
|
| 1 | +package com.brianway.learning.java.jvm.gc; |
| 2 | + |
| 3 | +/** |
| 4 | + * Created by brian on 17/3/3. |
| 5 | + * 对象可以在被 GC 时自我拯救 |
| 6 | + * 这种自救的机会只有一次,因为一个对象的 finalize() 方法最多只会被系统自动调用一次 |
| 7 | + */ |
| 8 | +public class FinalizeEscapeGC { |
| 9 | + public static FinalizeEscapeGC SAVE_HOOK = null; |
| 10 | + |
| 11 | + public void isAlive() { |
| 12 | + System.out.println("yes, i am still alive :)"); |
| 13 | + } |
| 14 | + |
| 15 | + @Override |
| 16 | + protected void finalize() throws Throwable { |
| 17 | + super.finalize(); |
| 18 | + System.out.println("finalize method executed"); |
| 19 | + FinalizeEscapeGC.SAVE_HOOK = this; |
| 20 | + } |
| 21 | + |
| 22 | + public static void main(String[] args) throws Throwable { |
| 23 | + SAVE_HOOK = new FinalizeEscapeGC(); |
| 24 | + |
| 25 | + //对象第一次成功拯救自己 |
| 26 | + SAVE_HOOK = null; |
| 27 | + System.gc(); |
| 28 | + |
| 29 | + // finalize 优先级低,暂停 0.5 秒以等待 |
| 30 | + Thread.sleep(500); |
| 31 | + |
| 32 | + if (SAVE_HOOK != null) { |
| 33 | + SAVE_HOOK.isAlive(); |
| 34 | + } else { |
| 35 | + System.out.println("no, i ma dead :("); |
| 36 | + } |
| 37 | + |
| 38 | + //与上面完全相同,缺失败 |
| 39 | + SAVE_HOOK = null; |
| 40 | + System.gc(); |
| 41 | + |
| 42 | + // finalize 优先级低,暂停 0.5 秒以等待 |
| 43 | + Thread.sleep(500); |
| 44 | + |
| 45 | + if (SAVE_HOOK != null) { |
| 46 | + SAVE_HOOK.isAlive(); |
| 47 | + } else { |
| 48 | + System.out.println("no, i ma dead :("); |
| 49 | + } |
| 50 | + |
| 51 | + } |
| 52 | +} |
| 53 | + |
| 54 | +/* |
| 55 | +finalize method executed |
| 56 | +yes, i am still alive :) |
| 57 | +no, i ma dead :( |
| 58 | + */ |
Collapse file
Copy file name to clipboard +31Lines changed: 31 additions & 0 deletions | Original file line number | Diff line number | Diff line change |
|---|
|
| 1 | +package com.brianway.learning.java.jvm.gc; |
| 2 | + |
| 3 | +/** |
| 4 | + * Created by brian on 17/3/2. |
| 5 | + * 引用计数算法缺陷 |
| 6 | + */ |
| 7 | +public class ReferenceCountingGC { |
| 8 | + public Object instance = null; |
| 9 | + private static final int _1MB = 1024 * 1024; |
| 10 | + |
| 11 | + /** |
| 12 | + * 占点内存,以便 GC 日志观看 |
| 13 | + */ |
| 14 | + private byte[] bigSize = new byte[2 * _1MB]; |
| 15 | + |
| 16 | + public static void main(String[] args) { |
| 17 | + testGC(); |
| 18 | + } |
| 19 | + |
| 20 | + public static void testGC() { |
| 21 | + ReferenceCountingGC objA = new ReferenceCountingGC(); |
| 22 | + ReferenceCountingGC objB = new ReferenceCountingGC(); |
| 23 | + objA.instance = objB; |
| 24 | + objB.instance = objA; |
| 25 | + |
| 26 | + objA = null; |
| 27 | + objB = null; |
| 28 | + |
| 29 | + System.gc(); |
| 30 | + } |
| 31 | +} |