Add a Once primitive
#11187
Add a Once primitive
#11187
Conversation
Of the 8 static mutexes that are currently in-use by the compiler and its libraries, 4 of them are currently used for one-time initialization. The unforunate side effect of using a static mutex is that the mutex is leaked. This primitive should provide the basis for efficiently keeping track of one-time initialization as well as ensuring that it does not leak the internal mutex that is used. I have chosen to put this in libstd because libstd is currently making use of a static initialization mutex (rt::local_ptr), but I can also see a more refined version of this type being suitable to initialize FFI bindings (such as initializing LLVM and initializing winsock networking on windows). I also intend on adding "helper threads" to libnative, and those will greatly benefit from a simple "once" primitive rather than always reinventing the wheel by using mutexes and bools. I would much rather see this primitive built on a mutex that blocks green threads appropriately, but that does not exist at this time, so it does not belong outside of `std::unstable`.
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A |
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You are correct. This is not a perf-sensitive piece of code, if you're invoking a Regardless, a |
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This might be better called |
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Maybe |
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Oh, I didn't realize this was mutex-specific. |
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I should have read the code before commenting. Now I understand what this is about. I'm not sure that this is appropriate in |
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@alexcrichton: It seems to me that Rust should stop being overly opinionated and let you initialize statics as you can in C++. It's a significant performance hit to need branches like this in every function using some globally initialized state. The work has to happen at some point, so why not run it before |
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Let's discuss life before main in a different issue, that is not the topic of this pull request. @brson, no particular reason to use a |
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Updated to remove the usage of |
Rationale can be found in the first commit, but this is basically the same thing as `pthread_once`
Rationale can be found in the first commit, but this is basically the same thing as
pthread_once