Thread Synchronization: A single flow of execution logic in a program. Enable your program to perform concurrent processing. Increases  efficiency and responsiveness. Share resources. Unpredictable execution order.

1. THREAD SYNCHRONIZATION

2. THREAD
 a single flow of execution logic in a program.
 Enable your program to perform concurrent
processing.
 Increases efficiency and responsiveness.
 Share resources.
 Unpredictable execution order.

3. SYECHROIZATION
 Simultaneous access to shared resource can cause
inconsistent and incorrect output.
 Introduce resource-sharing issues such as
deadlocks and race conditions
 So, the need of synchronized access to the shared
resources.
 System. Threading namespace.

4. PROBLEM
 Two threads updating a single shared variable
 One thread wants to decrement amount by 10K
 The other thread wants to decrement amount by 50%
amount= 100000;
…
…
amount = 0.50 * amount;
…
…
…
…
amount= amount - 10000;
…
…

5. RESULT
UNPREDICATBLE

6. (CASE 1)
…
r1 = load from amount
r1 = r1 - 10000;
store r1 to amount
…
…
r1 = load from amount
r1 = 0.5 * r1
store r1 to amount
…
amount= 100000;
amount= ?

7. (CASE 2)
…
r1 = load from amount
r1 = r1 - 10000;
store r1 to amount
…
…
r1 = load from amount
r1 = 0.5 * r1
store r1 to amount
…
amount= 100000;
amount= ?

8. (CASE 3)
…
r1 = load from amount
r1 = r1 - 10000;
store r1 to amount
…
…
r2 = load from amount
r2 = 0.5 * r2
store r2 to amount
…
amount= 100000;
amount= ?

9. SOLUTION
1. Lock
2. Monitor
3. Mutex
4. Semaphore

10. LOCK
 The lock allows us to define a scope of code that
must be synchronized between threads so that
incoming threads cannot interrupt the current
thread.
 Syntax-
…
lock(ThreadLock)
{
// Critical Section
}
….

11. MONITOR
 The lock is just a shorthand notation for working
with the System.Threading.Monitor class.
 Syntax-
Monitor.Enter(threadLock);
…
//Critical Section
…
Monitor.Exit(threadLock);

12. WHY MONITOR ???
 If we use the Monitor, we're able to tell the active
thread to wait by using Wait() method and let the
waiting threads know when the current thread is
completed via Pulse() and PulseAll() methods.

13. MUTEX
 A Mutex is similar to the lock, however, it can work
across multiple processes. But it is slower than
the lock.
 Mutex allows us to call the WaitOne() method to
lock and ReleaseMutex() to unlock.
 a Mutex can be released only from the same
thread which obtained it.
 The primary use for a cross-process Mutex is to
ensure that only one instance of a program can run
at a time

14. MUTEX
 Syntax-
static Mutex mutex = new Mutex();
Mutex.waitone()
…..
…..
Mutex.ReleaseMutex();

15. SEMAPHORE
 A Semaphore with a capacity of one is like
a Mutex or lock. However, the Semaphore has
no owner.
 We can use Semaphores to limit concurrency by
preventing too many threads from executing a
particular piece of code at once.
 Syntax-
// 4 available from capacity of 5 static
Semaphore semaphore = new Semaphore(4,5);
…
semaphore.WaitOne();
//critical section
semaphore.Release();
…