A mechanism that waits for ownership by repeatedly trying while consuming CPU execution time. A spinlock built from test-and-set can enforce mutual exclusion without guaranteeing starvation freedom. Progress also requires the owner to run and release: if a waiting software thread monopolizes the only CPU while the owner is suspended, exclusive entry alone cannot help.[ref]
An atomic read-modify-write that returns a flag's old value while setting it. In a sequential consistency model with the flag initially , exchange(flag, 1) permits entry only when it returns ; an owner resets the flag to on release. Between releases only one exchange can observe . By contrast, separate read(flag) and write(flag, 1) steps allow both contenders to read before either writes . The indivisibility of the exchange is an assumed primitive, not something proved by writing its steps as ordinary assignments.[ref]

Ancestors (8)

  1. Mutex
  2. Mutual exclusion
  3. Synchronization (computing)
  4. Thread (computing)
  5. Process (computing)
  6. Operating system
  7. Computer science
  8. Home

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