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1 package com.daffodilwoods.daffodildb.server.datasystem.utility;
2
3 import java.util.*;
4
5 public class SimpleFIFOReadWriteLocker implements ReadWriteLock {
6 boolean tableLocked= false;
7 Object  monitor = new Object ();
8 Vector waiters = new Vector(10);
9
10 TableLock tableLock = new TableLock();
11 RowLock rowLock = new RowLock();
12
13
14 public SimpleFIFOReadWriteLocker() {
15 }
16
17 private class TableLock{
18 Object owner;
19 int waitingThreads=0;
20
21 synchronized void incrementWaiters(){
22 ++waitingThreads;
23 }
24
25 synchronized void decrementWaitersToZero(){
26 waitingThreads = 0;
27 }
28
29 synchronized int waitersCount(){
30 return waitingThreads;
31 }
32 }
33
34 private class RowLock{
35 Object owner; int readersCount;
37 private int waitingThreads;
38
39 synchronized void increment(){
40 ++readersCount;
41 }
42
43 synchronized void decrement(){
44 --readersCount;
45 }
46
47 synchronized int readersCount(){
48 return readersCount;
49 }
50
51 synchronized void incrementWaiters(){
52 ++waitingThreads;
53 }
54
55 synchronized void decrementWaitersToZero(){
56 waitingThreads = 0;
57 }
58
59 synchronized int waitingThreads(){
60 return waitingThreads;
61 }
62 }
63
64 private class Wait{
65 boolean rowLock;
66
67 public synchronized void doWait(){
68 try {
69 wait(5);
70 }catch (InterruptedException ex) {
71 }
72 }
73
74 public synchronized void signal(){
75 notify();
76 }
77 }
78
79 private void waitOnTableLock(){
80 Wait tw = new Wait();
81 tw.rowLock = false;
82 waiters.add(tw);
83 do{
84 tw.doWait();
85 }while( (tableLocked || rowLock.readersCount() > 0) || (waiters.indexOf(tw) != 0) );
86 waiters.remove(0);
87 }
88
89 private void waitOnRowLock(){
90 Wait tw = new Wait();
91 tw.rowLock = true;
92 waiters.add(tw);
93 do{
94 tw.doWait();
95 }while( tableLocked || (waiters.indexOf(tw) != 0) );
96 waiters.remove(0);
97 }
98
99 ArrayList notifiers = new ArrayList();
100
101 private void notifyOnTableLock(){
102 boolean flag = true;
103 try{
104 for (int i = 0;flag && i < waiters.size(); i++) {
105 Wait w = (Wait)waiters.get(i);
106 if( w.rowLock == false ){
107 flag = false; if( notifiers.size() == 0 )
109 notifiers.add(w);
110 }
111 else{
112 notifiers.add(w);
113 }
114 }
115 }catch(ArrayIndexOutOfBoundsException ae){
116 }
117 for (int i = 0,size = notifiers.size(); i < size; i++) {
118 Wait w = (Wait) notifiers.get(i);
119 w.signal();
120 }
121 notifiers.clear();
122 }
123
124 public void lockTable() {
125 for(;;){
126 if( tableLocked ){
127 waitOnTableLock();
128 }
129 else if ( rowLock.readersCount() > 0 )
130 {
131 tableLock.incrementWaiters();
132 waitOnTableLock();
133 }
134 else{
135 synchronized( monitor ){
136 if( rowLock.readersCount() == 0 && tableLocked == false){
137 tableLocked = true;
138 tableLock.decrementWaitersToZero();
139 tableLock.owner = Thread.currentThread();
140 return;
141 }
142 }
143 }
144 }
145 }
146
147 public void releaseTable() {
148 synchronized( monitor ) {
149 tableLock.owner = null;
150 notifyOnTableLock();
151 tableLocked = false;
152 }
153 }
154
155 public void lockRowForRead(Object rowIdentity) {
156 for (; ; ) {
157 if (tableLocked) {
158 waitOnRowLock();
159 }
160 else if (tableLock.waitersCount() > 0) {
161 waitOnRowLock();
162 }
163 else {
164 synchronized (monitor) {
165 if (tableLocked == false) {
166 rowLock.increment();
167 return;
168 }
169 }
170 }
171 }
172 }
173
174 public void releaseRowForRead(Object rowIdentity) {
175 synchronized(monitor){
176 tableLocked = true;
177 rowLock.decrement();
178
179 if (rowLock.readersCount() == 0 && tableLock.waitersCount() > 0 )
180 notifyOnTableLock();
181 tableLocked = false;
182 }
183 }
184
185 public void lockRowForWrite(Object rowIdentity) {
186 lockTable();
187 }
188
189 public void releaseRowForWrite(Object rowIdentity) {
190 releaseTable();
191 }
192
193 }
194 |
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