Commit 0ebc64a
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- java-jvm/src/main/java/com/brianway/learning/java/jvm/gc
Lines changed: 58 additions & 0 deletions
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| 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 | + */ | ||
Lines changed: 31 additions & 0 deletions
| Original file line number | Diff line number | Diff line change | |
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| 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 | + } | ||
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