CLR multithreading, Part 1

A process is an inner container which has its own virtual address space
Libraries of code are mapped into the address spaces
A thread is path of execution through code within a single process.
For managed threads within an AppDomain
Each thread has it’s own callstack and copy of cpu registers

Advantages:
1. Better cpu utilization when a process runs on multiple core cpu or multiple processors machine.
2. Better support for asynchronous I/O operations. Performing CPU bound operations while waiting to complete I/O bound operations
3. Better UI responsiveness

Disadvantages:
Context switching overhead

Added program complexity:
1. More lines of code
2. Hard to maintain (readability)
3. Hard to debug
4. Hard to test

CLR thread class name
System.Threading.Thread

Thread life time:
Execution continues until thread returns from its entry point.
1. As a result of a standard method return.
2. As result of unhandled exception
1. As an exception caused by the running thread
2. As a result of calling Abort(), Interrupt() methods.

Coordinated thread shut-down
1. User-defined mechanism
2. Requesting thread waits:
2.1 Polling IsAlive
2.2. Calling Thread.Join

Thread Pool
CLR provides per process thread pool
1. Whenever thread is created a few microseconds goes on creating a thread stack and for allocating a memory. Thread pooll cuts overhead by sharing and recycling threads.
2. CLRs pool manager add thread or removes thread from a thread pool on demand.
3. IsBackground property is set to false

When not to use a thread pool
1. When we need foreground thread
2. When we need to set priority to the thread
3. When we run a long running task
4. When we need to identify a thread

Delegates and Async I/O

1. Delegates BeginInvoke queue a request method to the ThreaPool

private int AddMethod(int x)
{
return (unchecked)i++;
}

private delegate string OperationMethod(int x);

OperationMethod test = Method;
test.BeginInvoke(0, null, null);

2.
2.1 In case of Async I/O when we call I/O methods such as BeginRead, BeginWrite these methods calls goes to I/O completion port and these methods do not block the thread.
2.2. When Async I/O methods complete only then this call is queued to the ThreadPool.

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