Java中的锁(Locks in Java)
- - 并发编程网 - ifeve.com原文链接 作者:Jakob Jenkov 译者:申章 校对:丁一. 锁像synchronized同步块一样,是一种线程同步机制,但比Java中的synchronized同步块更复杂. 因为锁(以及其它更高级的线程同步机制)是由synchronized同步块的方式实现的,所以我们还不能完全摆脱synchronized关键字( 译者注:这说的是Java 5之前的情况).
package org.hashids; import java.util.ArrayList; import java.util.List; import java.util.regex.Matcher; import java.util.regex.Pattern; /** * Hashids designed for Generating short hashes from numbers (like YouTube and Bitly), obfuscate * database IDs, use them as forgotten password hashes, invitation codes, store shard numbers. * <p> * This is implementation of http://hashids.org v1.0.0 version. * * This implementation is immutable, thread-safe, no lock is necessary. * * @author <a href="mailto:[email protected]">fanweixiao</a> * @author <a href="mailto:[email protected]">Tercio Gaudencio Filho</a> * @since 0.3.3 */ public class Hashids { /** * Max number that can be encoded with Hashids. */ public static final long MAX_NUMBER = 9007199254740992L; private static final String DEFAULT_ALPHABET = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890"; private static final String DEFAULT_SEPS = "cfhistuCFHISTU"; private static final String DEFAULT_SALT = ""; private static final int DEFAULT_MIN_HASH_LENGTH = 0; private static final int MIN_ALPHABET_LENGTH = 16; private static final double SEP_DIV = 3.5; private static final int GUARD_DIV = 12; private final String salt; private final int minHashLength; private final String alphabet; private final String seps; private final String guards; public Hashids() { this(DEFAULT_SALT); } public Hashids(String salt) { this(salt, 0); } public Hashids(String salt, int minHashLength) { this(salt, minHashLength, DEFAULT_ALPHABET); } public Hashids(String salt, int minHashLength, String alphabet) { this.salt = salt != null ? salt : DEFAULT_SALT; this.minHashLength = minHashLength > 0 ? minHashLength : DEFAULT_MIN_HASH_LENGTH; final StringBuilder uniqueAlphabet = new StringBuilder(); for (int i = 0; i < alphabet.length(); i++) { if (uniqueAlphabet.indexOf(String.valueOf(alphabet.charAt(i))) == -1) { uniqueAlphabet.append(alphabet.charAt(i)); } } alphabet = uniqueAlphabet.toString(); if (alphabet.length() < MIN_ALPHABET_LENGTH) { throw new IllegalArgumentException( "alphabet must contain at least " + MIN_ALPHABET_LENGTH + " unique characters"); } if (alphabet.contains(" ")) { throw new IllegalArgumentException("alphabet cannot contains spaces"); } // seps should contain only characters present in alphabet; // alphabet should not contains seps String seps = DEFAULT_SEPS; for (int i = 0; i < seps.length(); i++) { final int j = alphabet.indexOf(seps.charAt(i)); if (j == -1) { seps = seps.substring(0, i) + " " + seps.substring(i + 1); } else { alphabet = alphabet.substring(0, j) + " " + alphabet.substring(j + 1); } } alphabet = alphabet.replaceAll("\\s+", ""); seps = seps.replaceAll("\\s+", ""); seps = Hashids.consistentShuffle(seps, this.salt); if ((seps.isEmpty()) || (((float) alphabet.length() / seps.length()) > SEP_DIV)) { int seps_len = (int) Math.ceil(alphabet.length() / SEP_DIV); if (seps_len == 1) { seps_len++; } if (seps_len > seps.length()) { final int diff = seps_len - seps.length(); seps += alphabet.substring(0, diff); alphabet = alphabet.substring(diff); } else { seps = seps.substring(0, seps_len); } } alphabet = Hashids.consistentShuffle(alphabet, this.salt); // use double to round up final int guardCount = (int) Math.ceil((double) alphabet.length() / GUARD_DIV); String guards; if (alphabet.length() < 3) { guards = seps.substring(0, guardCount); seps = seps.substring(guardCount); } else { guards = alphabet.substring(0, guardCount); alphabet = alphabet.substring(guardCount); } this.guards = guards; this.alphabet = alphabet; this.seps = seps; } /** * Encode numbers to string * * @param numbers * the numbers to encode * @return the encoded string */ public String encode(long... numbers) { if (numbers.length == 0) { return ""; } for (final long number : numbers) { if (number < 0) { return ""; } if (number > MAX_NUMBER) { throw new IllegalArgumentException("number can not be greater than " + MAX_NUMBER + "L"); } } return this._encode(numbers); } /** * Decode string to numbers * * @param hash * the encoded string * @return decoded numbers */ public long[] decode(String hash) { if (hash.isEmpty()) { return new long[0]; } String validChars = this.alphabet + this.guards + this.seps; for (int i = 0; i < hash.length(); i++) { if(validChars.indexOf(hash.charAt(i)) == -1) { return new long[0]; } } return this._decode(hash, this.alphabet); } /** * Encode hexa to string * * @param hexa * the hexa to encode * @return the encoded string */ public String encodeHex(String hexa) { if (!hexa.matches("^[0-9a-fA-F]+$")) { return ""; } final List<Long> matched = new ArrayList<Long>(); final Matcher matcher = Pattern.compile("[\\w\\W]{1,12}").matcher(hexa); while (matcher.find()) { matched.add(Long.parseLong("1" + matcher.group(), 16)); } // conversion final long[] result = new long[matched.size()]; for (int i = 0; i < matched.size(); i++) { result[i] = matched.get(i); } return this.encode(result); } /** * Decode string to numbers * * @param hash * the encoded string * @return decoded numbers */ public String decodeHex(String hash) { final StringBuilder result = new StringBuilder(); final long[] numbers = this.decode(hash); for (final long number : numbers) { result.append(Long.toHexString(number).substring(1)); } return result.toString(); } public static int checkedCast(long value) { final int result = (int) value; if (result != value) { // don't use checkArgument here, to avoid boxing throw new IllegalArgumentException("Out of range: " + value); } return result; } /* Private methods */ private String _encode(long... numbers) { long numberHashInt = 0; for (int i = 0; i < numbers.length; i++) { numberHashInt += (numbers[i] % (i + 100)); } String alphabet = this.alphabet; final char ret = alphabet.charAt((int) (numberHashInt % alphabet.length())); long num; long sepsIndex, guardIndex; String buffer; final StringBuilder ret_strB = new StringBuilder(this.minHashLength); ret_strB.append(ret); char guard; for (int i = 0; i < numbers.length; i++) { num = numbers[i]; buffer = ret + this.salt + alphabet; alphabet = Hashids.consistentShuffle(alphabet, buffer.substring(0, alphabet.length())); final String last = Hashids.hash(num, alphabet); ret_strB.append(last); if (i + 1 < numbers.length) { if (last.length() > 0) { num %= (last.charAt(0) + i); sepsIndex = (int) (num % this.seps.length()); } else { sepsIndex = 0; } ret_strB.append(this.seps.charAt((int) sepsIndex)); } } String ret_str = ret_strB.toString(); if (ret_str.length() < this.minHashLength) { guardIndex = (numberHashInt + (ret_str.charAt(0))) % this.guards.length(); guard = this.guards.charAt((int) guardIndex); ret_str = guard + ret_str; if (ret_str.length() < this.minHashLength) { guardIndex = (numberHashInt + (ret_str.charAt(2))) % this.guards.length(); guard = this.guards.charAt((int) guardIndex); ret_str += guard; } } final int halfLen = alphabet.length() / 2; while (ret_str.length() < this.minHashLength) { alphabet = Hashids.consistentShuffle(alphabet, alphabet); ret_str = alphabet.substring(halfLen) + ret_str + alphabet.substring(0, halfLen); final int excess = ret_str.length() - this.minHashLength; if (excess > 0) { final int start_pos = excess / 2; ret_str = ret_str.substring(start_pos, start_pos + this.minHashLength); } } return ret_str; } private long[] _decode(String hash, String alphabet) { final ArrayList<Long> ret = new ArrayList<Long>(); int i = 0; final String regexp = "[" + this.guards + "]"; String hashBreakdown = hash.replaceAll(regexp, " "); String[] hashArray = hashBreakdown.split(" "); if (hashArray.length == 3 || hashArray.length == 2) { i = 1; } if (hashArray.length > 0) { hashBreakdown = hashArray[i]; if (!hashBreakdown.isEmpty()) { final char lottery = hashBreakdown.charAt(0); hashBreakdown = hashBreakdown.substring(1); hashBreakdown = hashBreakdown.replaceAll("[" + this.seps + "]", " "); hashArray = hashBreakdown.split(" "); String subHash, buffer; for (final String aHashArray : hashArray) { subHash = aHashArray; buffer = lottery + this.salt + alphabet; alphabet = Hashids.consistentShuffle(alphabet, buffer.substring(0, alphabet.length())); ret.add(Hashids.unhash(subHash, alphabet)); } } } // transform from List<Long> to long[] long[] arr = new long[ret.size()]; for (int k = 0; k < arr.length; k++) { arr[k] = ret.get(k); } if (!this.encode(arr).equals(hash)) { arr = new long[0]; } return arr; } private static String consistentShuffle(String alphabet, String salt) { if (salt.length() <= 0) { return alphabet; } int asc_val, j; final char[] tmpArr = alphabet.toCharArray(); for (int i = tmpArr.length - 1, v = 0, p = 0; i > 0; i--, v++) { v %= salt.length(); asc_val = salt.charAt(v); p += asc_val; j = (asc_val + v + p) % i; final char tmp = tmpArr[j]; tmpArr[j] = tmpArr[i]; tmpArr[i] = tmp; } return new String(tmpArr); } private static String hash(long input, String alphabet) { String hash = ""; final int alphabetLen = alphabet.length(); do { final int index = (int) (input % alphabetLen); if (index >= 0 && index < alphabet.length()) { hash = alphabet.charAt(index) + hash; } input /= alphabetLen; } while (input > 0); return hash; } private static Long unhash(String input, String alphabet) { long number = 0, pos; for (int i = 0; i < input.length(); i++) { pos = alphabet.indexOf(input.charAt(i)); number = number * alphabet.length() + pos; } return number; } /** * Get Hashid algorithm version. * * @return Hashids algorithm version implemented. */ public String getVersion() { return "1.0.0"; } }