Synergy User Manual and Tutorial. - THE CORE MEMORY

Synergy User Manual and Tutorial
• Processor 1 writes: x = x + 1
• Processor 2 writes: x = x – 1
Depending on the possible orderings of the reads and writes the resulting variable could
be x–1, x+1 or x. This is a race condition and is an extremely undesirable because the
result depends on chance. Synchronization primitives, such as semaphores and monitors,
aid in the resolution of conflicts due to race conditions. The shared memory may be in a
single machine if it has more than one processor or a distributed shared memory, where
individual computers access the same memory area(s) located on another computer(s) on
the network.
Parallel processors must use some means to communicate. This is done on the system
buss and with shared memory in the case of a single computer with multiple processors.
When multiple machines are involved, communication can be implemented over a
network using either message passing or a distributed shared memory.
Cost is a very important consideration in distributed computing. A parallel system with n
processors is cheaper to build than a processor that is n-times faster. For tasks that need
to be completed quickly and can be performed by more than one thread of execution with
minimal concurrency, parallel processing is an exceptional solution. Many highperformance
or supercomputing machines have parallel processing architectures. The
parallel implementations discussed in the remainder of this book will be based on
distributed computing as opposed to single machines with multiple processors.
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