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Process Synchronization

Process Synchronization. Cooperating Processes. Process Cooperation Purposes Information sharing (Share files) Computation speedup (create subtasks to run simultaneously) Modularity (system function divide into separate processes or threads)

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Process Synchronization

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  1. Process Synchronization Cooperating Processes Process Cooperation Purposes • Information sharing (Share files) • Computation speedup (create subtasks to run simultaneously) • Modularity (system function divide into separate processes or threads) • Convenience (Run several tasks of the same user in the same environment at the same time)

  2. Inter process communication (IPC) mechanisms • Concurrent execution of cooperating processes requires mechanisms • that allow processes to communicate with one another • and to synchronize their actions. • Cooperating processes require an interprocess communication (IPC) mechanism that will allow them to exchange data and information to communicate and to synchronize. • OS provides those IPC mechanisms.

  3. IPC models There are two fundamental models of interprocess communication: (1) shared memory and (2) message passing. • In the shared-memorymodel • a region of memory that is shared by cooperating processes is established. • Processes can then exchange information by reading and writing data to the shared region. • In the message passingmodel • communication takes place by means of messages exchanged between the cooperating processes.

  4. IPC models Communications models. (a) Message passing. (b) Shared memory.

  5. IPC models. Tradeoff. • Shared Memory • Maximum speed (memory operations) • Convenience for sharing between local processes (simple write/read) • Difficult to implement for Inter Computer sharing or communication (needs polling). • Message Passing • Slow speed • (system calls, kernel intervention) • Complex to implement for inter process sharing. • data is sent by message • Easier to implement for Inter Process and Inter Computer communication / synchronization Communications models. (a) Message passing. (b) Shared memory.

  6. Producer Consumer paradigm • A producer process producesinformation • that is consumed by a consumer process. • The producer and consumer must be synchronized. • Web server produces HTML files and images which are consumed by the client • print program produces characters that are consumed by the printer driver

  7. Producer Consumer paradigmneeds synchronization The unbounded-buffer producer-consumer problem places no practical limit on the size of the buffer. Waiting means - Synchronization

  8. Producer Consumer paradigmmore synchronization The bounded-buffer assumes a fixed buffer size. The Bounded Buffer Problem - to make sure that the producer won't try to add data into the buffer if it's full and that the consumer won't try to remove data from an empty buffer.

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