what is the difference between semaphore, mutex &
spinlock?????
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Kernel Locking Techniques
Semaphores in Linux are sleeping locks. Because they cause a
task to sleep on contention, instead of spin, they are used
in situations where the lock-held time may be long.
Conversely, since they have the overhead of putting a task
to sleep and subsequently waking it up, they should not be
used where the lock-held time is short. Since they sleep,
however, they can be used to synchronize user contexts
whereas spinlocks cannot. In other words, it is safe to
block while holding a semaphore.
A "mutex" (or "mutual exclusion lock") is a signal that two
or more asynchronous processes can use to reserve a shared
resource for exclusive use. The first process that obtains
ownership of the "mutex" also obtains ownership of the
shared resource. Other processes must wait for for the first
process to release it's ownership of the "mutex" before they
may attempt to obtain it.
The most common locking primitive in the kernel is the
spinlock. The spinlock is a very simple single-holder lock.
If a process attempts to acquire a spinlock and it is
unavailable, the process will keep trying (spinning) until
it can acquire the lock. This simplicity creates a small and
fast lock.
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