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Golang Sync Mutex: Normal and Starvation Mode

39 points| lcof | 1 year ago |victoriametrics.com

14 comments

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mrkeen|1 year ago

> Mutex, or MUTual EXclusion, in Go is basically a way to make sure that only one goroutine is messing with a shared resource at a time. This resource can be a piece of code, an integer, a map, a struct, a channel, or pretty much anything.

This is untrue right? It can only protect code, not data, right?

lcof|1 year ago

The relationship with data is that it protects (controls) access to it

cstrahan|1 year ago

> This is untrue right? It can only protect code, not data, right?

Do traffic lights protect the flow of traffic, or do they protect people? It seems reductive to fixate on traffic lights stopping intersecting flows of traffic, when the intent is to ultimately protect people from slamming into (and thus injuring/killing) each other. It may be a tempting counterpoint that traffic lights don't do anything to protect someone from cancer, heart attack, etc -- but that's simply out of the scope of the protection that traffic lights are intended to provide.

Similarly, it seems odd to me to suggest that a mutex protects code -- what is it protecting that code from? How can the code be corrupted, damaged, or otherwise harmed? A mutex does prevent other non-lock-holding threads from running simultaneously, but that's all in service of protecting the data. The data is protected by imposing order on the execution of the code -- by serializing access to that data.

Controlling something isn't the same as protecting that something. A traffic light controls traffic, but it protects the people sharing the road. A mutex controls the execution of code, but it protects data.

jiveturkey|1 year ago

mutexes, in general, are considered to protect data. one associates a mutex with a piece of data. any number of bits of code might access that data, not just a single synchronized function.

Animats|1 year ago

I have misgivings about such long spinlocks in user space. A millisecond is over a million instructions.

Thorrez|1 year ago

Does the spinlock last a millisecond? It sounds from the article that it lasts 120 cycles.