Why would we use a multi threaded application vs. a single threaded application? First we must define multithreading. Multithreading is a feature of an operating system that allows programs to run subcomponents or threads in parallel. Typically most applications only need to use one thread because they do not perform time consuming tasks. The use of multiple threads allows an application to distribute long running tasks so that they can be executed in parallel. This gives the user the perceived appearance that the application is working faster due to the fact that while one thread is waiting on an IO process the remaining tasks can make use of the available CPU. The allows working threads to execute in tandem so that they can be competed sooner.
- Improved responsiveness — Users usually report improved responsiveness compared to single thread applications.
- Faster applications — Multiple threads can lead to improved application performance.
- Prioritization — Threads can be assigned a priority which would allow higher priority tasks to take precedence over lower priority tasks.
Single Threading Benefits
- Programming and debugging —These activities are easier compared to multithreaded applications due to the reduced complexity
- Less Overhead — Threads add overhead to an application
When developing multi-threaded applications, the following must be considered.
- Deadlocks occur when two threads hold a monitor that the other one requires. In essence each task is blocking the other and both tasks are waiting for the other monitor to be released. This forces an application to hang or deadlock.
- Resource allocation is used to prevent deadlocks because the system determines if approving the resource request will render the system in an unsafe state. An unsafe state could result in a deadlock. The system only approves requests that will lead to safe states.
- Thread Synchronization is used when multiple threads use the same instance of an object. The threads accessing the object can then be locked and then synchronized so that each task can interact with the static object on at a time.