Concurrency and Deadlocks Quiz

Deadlock in Systems

• In a system with no preemption, if a process holding resources requests another resource that is not immediately available, it will block and wait for the requested resource to become available. The process will not be forcibly removed from its current state.

• A process in a system with no preemption that cannot immediately access a requested resource will wait until the resource becomes available. The process will remain in a blocked state until the resource is released.

• Deadlock can be avoided in a system where each process requests resources in an increasing order of enumeration by implementing a resource ordering protocol. This protocol ensures that if a process requests resource R1 then R2, any other process requesting resources will request R1 before R2 as well.

• To avoid deadlocks based on the sequence of requests from active processes, the system needs to be aware of the current state of resource allocation and the order of resource requests from each process.

Deadlock in Disk Sharing

• In a system with no preemption, a process can be restarted only if it is not holding any resources. If the process is holding a resource, it cannot be restarted until the resource is released.

• A deadlock in disk sharing can occur when two or more processes are waiting for each other to release the same disk, leading to a circular dependency where no process can proceed.

• Deadlock in disk sharing happens when conflicting commands are issued by processes. For example, one process may try to write to a file while another tries to read the same file.

• A common characteristic of deadlocks in multiple device allocation is that they involve multiple resources (e.g., disk, tape drive, printer), and multiple processes competing for these resources.

Deadlock in Spooling

• Deadlock in spooling can occur when a program is waiting for a resource that is being held by another program, and both programs are waiting for each other. This can happen, for example, when one program needs to read data from a file that is currently being written to by another program.

• Deadlock in spooling can occur when two or more processes are waiting for the same spool file.

• The primary cause of deadlocks in spooling systems is the lack of a centralized resource allocation mechanism. This allows for processes to acquire resources in a way that can lead to deadlocks.

Deadlock in Networks

• Deadlocks in a network can occur when two or more devices are waiting for each other to transmit data. For instance, device A holds a resource needed by device B, and device B holds a resource needed by device A.

• A characteristic of a deadlock in disk sharing is that it involves multiple processes waiting for each other to release a specific disk.

• In a spooling system, if a program is in deadlock, it will be unable to proceed and will remain in a blocked state until the deadlock is resolved.

• Deadlocks in a network can occur when two or more nodes are waiting for each other to send data through shared links. This can happen if two nodes try to use the same link at the same time, leading to a circular dependency where no node can proceed.

Comparing Deadlocks

• A deadlock in spooling differs from a deadlock in disk sharing in the fact that spooling deadlocks usually involve multiple processes competing for a single shared resource, such as a spool file. Disk sharing deadlocks usually involve multiple processes competing for multiple shared resources, such as disks.

• A common characteristic of deadlocks in both spooling and network scenarios is that they involve a circular dependency where resources are held by multiple processes, each waiting for a resource held by another. This creates a standstill where none of the processes can proceed.

• Deadlocks on file requests differ from deadlocks in databases in that file requests typically involve low-level operations related to accessing a file on a disk. Deadlocks in databases, however, occur at a higher level, involving transactions and locks on data within the database.

Test your knowledge on concurrency issues in database systems, including locking, race conditions, and deadlocks. Learn about managing access to data at different levels of granularity and understanding the complexities that arise in multi-process environments.