util/concurrent/Helpers.java

/*
 * Written by Martin Buchholz with assistance from members of JCP
 * JSR-166 Expert Group and released to the public domain, as
 * explained at http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util.concurrent;

import java.util.Collection;

/** Shared implementation code for java.util.concurrent. */
class Helpers {
    /**
     * An implementation of Collection.toString() suitable for classes
     * with locks.  Instead of holding a lock for the entire duration of
     * toString(), or acquiring a lock for each call to Iterator.next(),
     * we hold the lock only during the call to toArray() (less
     * disruptive to other threads accessing the collection) and follows
     * the maxim "Never call foreign code while holding a lock".
     */
    static String collectionToString(Collection<?> c) {
        final Object[] a = c.toArray();
        final int size = a.length;
        if (size == 0)
            return "[]";
        int charLength = 0;

        // Replace every array element with its string representation
        for (int i = 0; i < size; i++) {
            Object e = a[i];
            // Extreme compatibility with AbstractCollection.toString()
            String s = (e == c) ? "(this Collection)" : objectToString(e);
            a[i] = s;
            charLength += s.length();
        }

        return toString(a, size, charLength);
    }

    /**
     * Like Arrays.toString(), but caller guarantees that size > 0,
     * each element with index 0 <= i < size is a non-null String,
     * and charLength is the sum of the lengths of the input Strings.
     */
    static String toString(Object[] a, int size, int charLength) {
        // assert a != null;
        // assert size > 0;

        // Copy each string into a perfectly sized char[]
        // Length of [ , , , ] == 2 * size
        final char[] chars = new char[charLength + 2 * size];
        chars[0] = '[';
        int j = 1;
        for (int i = 0; i < size; i++) {
            if (i > 0) {
                chars[j++] = ',';
                chars[j++] = ' ';
            }
            String s = (String) a[i];
            int len = s.length();
            s.getChars(0, len, chars, j);
            j += len;
        }
        chars[j] = ']';
        // assert j == chars.length - 1;
        return newStringUnsafe(chars);
    }

    /** Optimized form of: key + "=" + val */
    static String mapEntryToString(Object key, Object val) {
        final String k, v;
        final int klen, vlen;
        final char[] chars =
            new char[(klen = (k = objectToString(key)).length()) +
                     (vlen = (v = objectToString(val)).length()) + 1];
        k.getChars(0, klen, chars, 0);
        chars[klen] = '=';
        v.getChars(0, vlen, chars, klen + 1);
        return newStringUnsafe(chars);
    }

    private static String objectToString(Object x) {
        // Extreme compatibility with StringBuilder.append(null)
        String s;
        return (x == null || (s = x.toString()) == null) ? "null" : s;
    }

    /**
     * Returns a String containing the contents of chars, which caller
     * promises will never be modified.
     */
    private static String newStringUnsafe(char[] chars) {
        // If porting to a JDK where sun.misc.SharedSecrets is not
        // available, modify the code below to simply:
        // return new String(chars);
        // TODO: Can we do this more portably?
        return sun.misc.SharedSecrets.getJavaLangAccess().newStringUnsafe(chars);
    }

}
Revision:	1.1
Committed:	Wed Mar 4 00:22:30 2015 UTC (9 years, 3 months ago) by jsr166
Branch:	MAIN
Log Message:	optimize toString() methods; introduce Helpers
#	User	Rev	Content
1	jsr166	1.1	/*
2			* Written by Martin Buchholz with assistance from members of JCP
3			* JSR-166 Expert Group and released to the public domain, as
4			* explained at http://creativecommons.org/publicdomain/zero/1.0/
5			*/
6
7			package java.util.concurrent;
8
9			import java.util.Collection;
10
11			/** Shared implementation code for java.util.concurrent. */
12			class Helpers {
13			/**
14			* An implementation of Collection.toString() suitable for classes
15			* with locks. Instead of holding a lock for the entire duration of
16			* toString(), or acquiring a lock for each call to Iterator.next(),
17			* we hold the lock only during the call to toArray() (less
18			* disruptive to other threads accessing the collection) and follows
19			* the maxim "Never call foreign code while holding a lock".
20			*/
21			static String collectionToString(Collection<?> c) {
22			final Object[] a = c.toArray();
23			final int size = a.length;
24			if (size == 0)
25			return "[]";
26			int charLength = 0;
27
28			// Replace every array element with its string representation
29			for (int i = 0; i < size; i++) {
30			Object e = a[i];
31			// Extreme compatibility with AbstractCollection.toString()
32			String s = (e == c) ? "(this Collection)" : objectToString(e);
33			a[i] = s;
34			charLength += s.length();
35			}
36
37			return toString(a, size, charLength);
38			}
39
40			/**
41			* Like Arrays.toString(), but caller guarantees that size > 0,
42			* each element with index 0 <= i < size is a non-null String,
43			* and charLength is the sum of the lengths of the input Strings.
44			*/
45			static String toString(Object[] a, int size, int charLength) {
46			// assert a != null;
47			// assert size > 0;
48
49			// Copy each string into a perfectly sized char[]
50			// Length of [ , , , ] == 2 * size
51			final char[] chars = new char[charLength + 2 * size];
52			chars[0] = '[';
53			int j = 1;
54			for (int i = 0; i < size; i++) {
55			if (i > 0) {
56			chars[j++] = ',';
57			chars[j++] = ' ';
58			}
59			String s = (String) a[i];
60			int len = s.length();
61			s.getChars(0, len, chars, j);
62			j += len;
63			}
64			chars[j] = ']';
65			// assert j == chars.length - 1;
66			return newStringUnsafe(chars);
67			}
68
69			/** Optimized form of: key + "=" + val */
70			static String mapEntryToString(Object key, Object val) {
71			final String k, v;
72			final int klen, vlen;
73			final char[] chars =
74			new char[(klen = (k = objectToString(key)).length()) +
75			(vlen = (v = objectToString(val)).length()) + 1];
76			k.getChars(0, klen, chars, 0);
77			chars[klen] = '=';
78			v.getChars(0, vlen, chars, klen + 1);
79			return newStringUnsafe(chars);
80			}
81
82			private static String objectToString(Object x) {
83			// Extreme compatibility with StringBuilder.append(null)
84			String s;
85			return (x == null \|\| (s = x.toString()) == null) ? "null" : s;
86			}
87
88			/**
89			* Returns a String containing the contents of chars, which caller
90			* promises will never be modified.
91			*/
92			private static String newStringUnsafe(char[] chars) {
93			// If porting to a JDK where sun.misc.SharedSecrets is not
94			// available, modify the code below to simply:
95			// return new String(chars);
96			// TODO: Can we do this more portably?
97			return sun.misc.SharedSecrets.getJavaLangAccess().newStringUnsafe(chars);
98			}
99
100			}