Sharing a Domain Device with Threads

When numerous threads attempt to access a domain device simultaneously, we enter into the realm of a Thread-Safe environment. When more than one thread competes for access to an object simultaneously, some threads may receive an invalid state if another thread modifies the resource at the same time. For example, if a robot attempt to access objects on a conveyor belt while another robot is operating on that same conveyor belt, the first thread (robot) may receive an invalid state of access (Zhai et al., 2012). This situation leads to what is known as a race condition.

What's notable is the profound ability to use synchronization techniques that prevent thread interference of shared objects through calls to a method that will lock the thread. In this scenario, no other thread can access the conveyor belt until completing the current thread's (robot's) execution (Basile et al., 2002).

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The Semaphore Safe Thread Regarding the Robot and the Conveyor

We can use semaphores when dealing with a conveyor system in which there is a single robot that needs access to a multi-accessed conveyor system.

Preventing simultaneous access to the conveyor system is an issue and can be solved using a semaphore. In the robot-conveyor case, the robot must wait before accessing an atomic conveyor system until the semaphore is in a state that allows access to acquire objects. When the robot accesses the conveyor belt, the semaphore changes state to stop other robots from accessing the conveyor system (Moiseev, 2010). A robot that has completed it's conveyor access operations changes the semaphore state to permit another robot to access the conveyor belt.

In the robot-conveyor scenario, a semaphore could be a simple number. More specifically, a robot waits for permission to proceed. It then messages other robots a flag indicating it has proceeded by implementing a numerical value on the semaphore's operation.

The Garage State Machine

Below is a state machine that depicts the state of a garage door opening and closing operations provided with specific time and emergency conditions. It also illustrates state changes with cause and effect of additional actions based on either remote control triggers or emergency conditions. Many of the states shown in the diagram below refer to the various inputs from devices that affect the garage's behavior. To fully demonstrate the garage's multiple states, I provided a comprehensive state machine diagram that presents states' full visualization and how the garage door transitions to each state (Alonso et al., 2008).

The state diagram below (fig.1) begins with a green start icon and a square titled "garage closed" as the initial state and ends with a square titled "garage closed" as the final state. However, as you will witness, many conditions and triggers affect the garage door events' progression. The behavior of the garage door is illustrated clearly in transitory order from garage operational state to state.

References

 

Alonso, D., Vicente-Chicote, C., Pastor, J. A., & Álvarez, B. (2008). Stateml+: From graphical state machine models to thread-safe ada code. International Conference on Reliable Software Technologies,

Basile, C., Whisnant, K., Kalbarczyk, Z., & Iyer, R. (2002). Loose synchronization of multithreaded replicas. 21st IEEE Symposium on Reliable Distributed Systems, 2002. Proceedings.,

Moiseev, M. (2010). Defect detection for multithreaded programs with semaphore-based synchronization. 2010 6th Central and Eastern European Software Engineering Conference (CEE-SECR),

Zhai, K., Xu, B., Chan, W., & Tse, T. (2012). CARISMA: a context-sensitive approach to race-condition sample-instance selection for multithreaded applications. Proceedings of the 2012 International Symposium on Software Testing and Analysis,