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CSC 246 Exam 2 Terms in this set (76) thread Sequential flow of action executed by a process; executes only one task at a time, while a multithreaded process can execute a task per thread. Multithread Multiple tasks can be implemented by separate$5.99
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CSC 246 Exam 2 Terms in this set (76) thread Sequential flow of action executed by a process; executes only one task at a time, while a multithreaded process can execute a task per thread. Multithread Multiple tasks can be implemented by separate
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CGFO - Certified Government Finance Officer
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CGFO - Certified Government Finance Officer
CSC 246 Exam 2
Terms in this set (76)
thread Sequential flow of action executed by a process; executes only one task at a time, while a multithreaded process can execute a task per thread.
Multithread Multiple tasks can be implemented by separate threads; more efficient than creati...
Sequential flow of action executed by a process; executes only one task at a time, while
thread
a multithreaded process can execute a task per thread.
Multiple tasks can be implemented by separate threads; more efficient than creating
Multithread
multiple processes
Responsiveness (continues execution if part of process is blocked), Resource Sharing
Benefits (Threads share resources of process), Economy (cheaper than process creation),
Scalability (process can take advantage of multiprocessor architectures)
Parallelism System can perform more than one task simultaneously
Concurrency executing multiple tasks simultaneously in an overlapping manner
Threads share code, data, and files in multithreaded process, but not stacks, registers,
What threads share and don't
and state.
speedup is less than or equal to 1 / S + (1-S)/N. S is serial portion, N is processing cores.
Amdahl's Law
Identifies performance gains from adding additional cores to an application.
User threads Threads implemented by user software
Kernel threads Supported by the Kernel
Many-to-One Many user-level threads mapped to single kernel thread; one thread block blocks all
Each user-level thread maps to kernel thread (more concurrent than many-to-one)
One-to-One
(creating a user-level thread creates a kernel thread)
Allows many user level threads to be mapped to many kernel threads
Many-to-Many
Allows the operating system to create a sufficient number
of kernel threads
Two-level Similar to many-to-many; except it allows a user thread to be bound to kernel thread
Create a number of threads in a pool where they await work (slightly faster than
Thread pools
creating a new thread to service request)
Threading issues Signal handling, Fork() and exec() calls, thread cancellation of target thread
Signals Notify a process that a particular event has occurred
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User-defined or default; Used to process signals; generated by a particular event or
Signal handler delivered to a process; default handler run by kernel when handling signal (can be
overridden by user-defined signal handler)
Deferred cancellation allows the target thread to periodically check if it should be cancelled
Cancellation point Cancellation occurs when thread reaches this point, then cleanup handler is invoked
Thread-local storage Allows each thread to have its own copy of data
Context of thread register set, stacks, and private storage area
A thread contains Thread id, register set, separate user and kernel stacks, private data storage area
A process that can be affected or affect other processes executing in the system.
Cooperating process
Concurrent access to shared data may result in data inconsistency.
Producer produces item in buffer; consumer removes/decrements item from buffer.
Consumer-Producer problem Concurrent execution of statements can lead to inconsistent data (count++ and count--
when count is equal to 5 results in 4 and 6)
Race condition Situation where two threads are concurrently trying to change a variable's value
Process Synchronization Coordination of access to data by two or more threads or processes.
Consider a system consisting of n processes (p0, p1, ..., pn-1). Each process has a
segment of code called a critical section (A section of code responsible for changing
Critical Section Problem data that must only be executed by one thread or process at a time to avoid a race
condition). When one process is executing in its critical section, no other process is
allowed to execute in its critical section at the same time.
Entry section Section of code requesting permission to enter the critical section
Exit section The section of code within a process that cleanly exits the critical section
Remainder section Whatever code remains to be processed after critical and exit sections
Must satisfy:
mutual exclusion (if one process is executing in its critical section, no other process can
execute in their critical sections)
progress (If no process is executing in its critical section and some processes wish to
Solution to Critical Section Problem enter their critical sections, then those processes that are not executing in their
remainder sections can participate in deciding which will enter its critical section next
bounded waiting (there exists a bound on the number of times that other processes are
allowed to enter their critical sections after a process has made a request and before
that request is granted)
Kernel is preemptive Allows preemption of process when running in kernel mode
Kernel is non-preemptive Runs until exits kernel mode, blocks, or yields CPU
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