Diksamに例外処理をつけるため、Javaの仕様を参考にしようとしているんですが。
try catchのfinally節は、「何があっても通る」ところなので、たとえば以下のようなソースでは、
for (;;) {
try {
…
break;
} catch (Exception e) {
…
return;
} finally {
…
}
}try節の中のbreakやcatch節の中のreturnでfor文やメソッドを抜ける際でもfinallyの中は通らなければなりません。しかも、finally実行後に行うことはbreakだったりreturnだったりと異なるので、これは単にジャンプ命令で引き回すだけでは実現が難しそうです。
そのためにjsr(jump subroutine)という、関数内のサブルーチンコールのインストラクションがJVMにはあるのだと私は理解してました。
JVMの仕様書を見ると、
http://java.sun.com/docs/books/jvms/second_edition/html/Compiling.doc.html#13789
void tryFinally() {
try {
tryItOut();
} finally {
wrapItUp();
}
}というソースから、以下のようなバイトコードが生成されるそうです。
Method void tryFinally() 0 aload_0 // Beginning of try block 1 invokevirtual #6 // Method Example.tryItOut()V 4 jsr 14 // Call finally block 7 return // End of try block 8 astore_1 // Beginning of handler for any throw 9 jsr 14 // Call finally block 12 aload_1 // Push thrown value 13 athrow // ...and rethrow the value to the invoker 14 astore_2 // Beginning of finally block 15 aload_0 // Push this 16 invokevirtual #5 // Method Example.wrapItUp()V 19 ret 2 // Return from finally block Exception table: From To Target Type 0 4 8 any
添字4、9の箇所でfinallyの開始店である14バイト目にサブルーチンジャンプしています。
じゃあbreakとかreturnとか使ったら、その直前にjsrを出力するのかな、と思い、試してみました。
class ExceptionTest2 {
public static void main(String[] args) {
for (;;) {
try {
System.out.println("hello, world.");
break;
} catch (Exception e) {
System.out.println("catch");
} finally {
System.out.println("finally");
}
}
}
}これをコンパイルして、javap -cで見てみると… あれ?
public static void main(java.lang.String[]);
Code:
0: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
3: ldc #3; //String hello, world.
5: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
8: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
11: ldc #5; //String finally
13: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
16: goto 53
19: astore_1
20: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
23: ldc #7; //String catch
25: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
28: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
31: ldc #5; //String finally
33: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
36: goto 50
39: astore_2
40: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
43: ldc #5; //String finally
45: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
48: aload_2
49: athrow
50: goto 0
53: return
Exception table:
from to target type
0 8 19 Class java/lang/Exception
0 8 39 any
19 28 39 any
39 40 39 anyソースには3箇所しかないSystem.out.println()の呼び出しが5箇所に増えています。
finally節の「System.out.println("finally");」を、try節のbreakの直前とcatch節の末尾に複製しているように見えます。
finally節が短かったからコンパイラが展開しちゃったのかなあ、と思い、ちょっと長くしてみましたが、
class ExceptionTest3 {
public static void main(String[] args) {
for (;;) {
try {
System.out.println("hello, world.");
break;
} catch (Exception e) {
System.out.println("catch");
} finally {
System.out.println("finally1");
System.out.println("finally2");
System.out.println("finally3");
System.out.println("finally4");
System.out.println("finally5");
System.out.println("finally6");
System.out.println("finally7");
System.out.println("finally8");
System.out.println("finally9");
System.out.println("finally10");
System.out.println("finally11");
System.out.println("finally12");
System.out.println("finally13");
System.out.println("finally14");
}
}
}
}public static void main(java.lang.String[]);
Code:
0: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
3: ldc #3; //String hello, world.
5: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
8: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
11: ldc #5; //String finally1
13: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
16: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
19: ldc #6; //String finally2
21: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
24: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
27: ldc #7; //String finally3
29: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
32: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
35: ldc #8; //String finally4
37: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
40: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
43: ldc #9; //String finally5
45: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
48: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
51: ldc #10; //String finally6
53: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
56: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
59: ldc #11; //String finally7
61: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
64: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
67: ldc #12; //String finally8
69: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
72: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
75: ldc #13; //String finally9
77: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
80: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
83: ldc #14; //String finally10
85: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
88: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
91: ldc #15; //String finally11
93: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
96: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
99: ldc #16; //String finally12
101: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
104: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
107: ldc #17; //String finally13
109: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
112: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
115: ldc #18; //String finally14
117: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
120: goto 365
123: astore_1
124: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
127: ldc #20; //String catch
129: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
132: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
135: ldc #5; //String finally1
137: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
140: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
143: ldc #6; //String finally2
145: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
148: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
151: ldc #7; //String finally3
153: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
156: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
159: ldc #8; //String finally4
161: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
164: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
167: ldc #9; //String finally5
169: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
172: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
175: ldc #10; //String finally6
177: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
180: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
183: ldc #11; //String finally7
185: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
188: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
191: ldc #12; //String finally8
193: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
196: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
199: ldc #13; //String finally9
201: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
204: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
207: ldc #14; //String finally10
209: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
212: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
215: ldc #15; //String finally11
217: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
220: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
223: ldc #16; //String finally12
225: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
228: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
231: ldc #17; //String finally13
233: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
236: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
239: ldc #18; //String finally14
241: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
244: goto 362
247: astore_2
248: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
251: ldc #5; //String finally1
253: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
256: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
259: ldc #6; //String finally2
261: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
264: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
267: ldc #7; //String finally3
269: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
272: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
275: ldc #8; //String finally4
277: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
280: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
283: ldc #9; //String finally5
285: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
288: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
291: ldc #10; //String finally6
293: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
296: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
299: ldc #11; //String finally7
301: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
304: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
307: ldc #12; //String finally8
309: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
312: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
315: ldc #13; //String finally9
317: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
320: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
323: ldc #14; //String finally10
325: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
328: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
331: ldc #15; //String finally11
333: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
336: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
339: ldc #16; //String finally12
341: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
344: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
347: ldc #17; //String finally13
349: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
352: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
355: ldc #18; //String finally14
357: invokevirtual #4; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
360: aload_2
361: athrow
362: goto 0
365: return
Exception table:
from to target type
0 8 123 Class java/lang/Exception
0 8 247 any
123 132 247 any
247 248 247 any…いいのかなあ、これ。
ていうかそもそも仕様書にあるサンプルならjsrが出力されるのかよ、と、足りないコードを補って以下で試してみたんですが、
class TryFinally {
void tryItOut() {}
void wrapItUp() {}
void tryFinally() {
try {
tryItOut();
} finally {
wrapItUp();
}
}
}バイトコードはこうなりました。
void tryFinally();
Code:
0: aload_0
1: invokevirtual #2; //Method tryItOut:()V
4: aload_0
5: invokevirtual #3; //Method wrapItUp:()V
8: goto 18
11: astore_1
12: aload_0
13: invokevirtual #3; //Method wrapItUp:()V
16: aload_1
17: athrow
18: return
Exception table:
from to target type
0 4 11 any
11 12 11 any…えーっと。
※ javac 1.6.0_02にて。
