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Process Synchronization Dhamdhere: Operating Systems— Copyright © 2008
Process Synchronization
• Processes that work toward a common goal must coordinate their activities
– Such coordination is achieved through synchronization
– We discuss two kinds of synchronization defined in Chapter 3 * Data access synchronization
Avoiding race conditions through mutual exclusion
* Control synchronization
Ensuring that processes perform their actions in a desired order
Process Synchronization Dhamdhere: Operating Systems— Copyright © 2008
Interacting processes
• Definition:
– Processes Pi, Pj are interacting processes if
read_seti ∩ write_setj ≠ Ø or write_seti ∩ read_setj ≠ Ø,
where
* Read-set : Set of variables merely read by a process
* Write-set : Set of variables read and written to by a process – Non-interacting processes are independent processes
Process Synchronization Dhamdhere: Operating Systems— Copyright © 2008
Critical Section (CS)
• Definition
– A critical section (CS) for a data item ds is a section of code that cannot be executed concurrently with itself or with another critical section for ds
* We will use a dashed rectangular box to indicate a critical section in a code segment (see next slide)
• Data access synchronization
– Is defined as ensuring an absence of race conditions over a shared data item ds
* It is achieved by enclosing all uses of ds within critical sections
Process Synchronization Dhamdhere: Operating Systems— Copyright © 2008
A process having critical sections
We assume a process to consist of a single infinite loop; a dashed rectangular box depicts a critical section
(a) A process having many critical sections (b) A process having a single critical section
Process Synchronization Dhamdhere: Operating Systems— Copyright © 2008
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