C# 4 and .NET 4

synchronization ❘ 531
The ReaderWriterLockSlim class has properties to acquire a read lock that are blocking and nonblocking,
such as EnterReadLock() and TryEnterReadLock(), and to acquire a write lock with EnterWriteLock()
and TryEnterWriteLock(). If a task reads first and writes afterward, it can acquire an upgradable
read lock with EnterUpgradableReadLock() or TryEnterUpgradableReadLock(). With this lock,
the write lock can be acquired without releasing the read lock.
Several properties of this class offer information about the held locks, for example, CurrentReadCount,
WaitingReadCount, WaitingUpgradableReadCount, and WaitingWriteCount.
The sample program creates a collection containing six items and a ReaderWriterLockSlim object. The
method ReaderMethod() acquires a read lock to read all items of the list and write them to the console.
The method WriterMethod() tries to acquire a write lock to change all values of the collection. In the
Main() method, six threads are started that invoke either the method ReaderMethod() or the method
WriterMethod().
using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
namespace Wrox.ProCSharp.Threading
{
class Program
{
private static List items = new List() { 0, 1, 2, 3, 4, 5};
private static ReaderWriterLockSlim rwl =
new ReaderWriterLockSlim(LockRecursionPolicy.SupportsRecursion);
static void ReaderMethod(object reader)
{
try
{
rwl.EnterReadLock();
}
for (int i = 0; i < items.Count; i++)
{
Console.WriteLine("reader {0}, loop: {1}, item: {2}",
reader, i, items[i]);
Thread.Sleep(40);
}
}
finally
{
rwl.ExitReadLock();
}
static void WriterMethod(object writer)
{
try
{
while (!rwl.TryEnterWriteLock(50))
{
Console.WriteLine("Writer {0} waiting for the write lock",
writer);
Console.WriteLine("current reader count: {0}",
rwl.CurrentReadCount);
}
Console.WriteLine("Writer {0} acquired the lock", writer);
for (int i = 0; i < items.Count; i++)
{
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