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1 using System;
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2 using System.Threading;
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3 using System.Diagnostics;
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4
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5 namespace Implab.Parallels {
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6 /// <summary>
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7 /// Implements a lightweight mechanism to aquire a shared or an exclusive lock.
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8 /// </summary>
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9 public class SharedLock {
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10 readonly object m_lock = new object();
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11 int m_locks;
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12 bool m_exclusive;
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13
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14 public bool LockExclusive(int timeout) {
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15 lock (m_lock) {
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16 if (m_locks > 0 && !Monitor.Wait(m_lock, timeout))
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17 return false;
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18 m_exclusive = true;
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19 m_locks = 1;
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20 }
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21 }
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22
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23 public void LockExclusive() {
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24 LockExclusive(-1);
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25 }
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26
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27 public bool LockShared(int timeout) {
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28 lock (m_lock) {
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29 if (!m_exclusive) {
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30 m_locks++;
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31 return true;
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32 }
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33
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34 if (m_lock == 0) {
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35 m_exclusive = false;
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36 m_locks = 1;
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37 return true;
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38 }
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39
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40 if (Monitor.Wait(m_lock, timeout)) {
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41 Debug.Assert(m_locks == 0);
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42 m_locks = 1;
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43 m_exclusive = false;
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44 return true;
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45 }
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46 return false;
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47 }
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48 }
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49
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50 public void LockShared() {
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51 LockShared(-1);
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52 }
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53
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54 public void ReleaseShared() {
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55 lock (m_lock) {
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56 if (m_exclusive || m_locks <= 0)
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57 throw new InvalidOperationException();
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58 m_locks--;
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59 if (m_locks == 0)
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60 Monitor.PulseAll(m_lock);
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61 }
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62 }
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63
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64 public void ReleaseExclusive() {
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65 lock (m_lock) {
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66 if (!m_exclusive && m_locks != 1)
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67 throw new InvalidOperationException();
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68 m_locks = 0;
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69 Monitor.PulseAll(m_lock);
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70 }
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71 }
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72
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73 }
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74 }
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75
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