and why mutexes are also necessary.

Sorry, but that example is contrived to need a mutex. The signalling condition uses a global variable: Lock associated mutex and check value of a global variable.

Now consider the case of a signalling condition that doesn't involve a global variable. Then what use is the mutex?

As for the performance characteristics of mutexes. If I am misinformed, then so is half of the internet it seems.

With regard to your TCP/IP example. It is understandable that mutexes are not a bottleneck where IO is involved. Even the 300 to 400 cycles that it takes to make a ring3 - ring0 - ring3 transition pale when compared to IO waits.

But user-space only, atomic instructions, even with barrier instructions are much faster for memory to memory operations.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

In reply to Re^2: OT: Locking and syncing mechanisms available on *nix. by BrowserUk
in thread OT: Locking and syncing mechanisms available on *nix. by BrowserUk

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