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wasi-libc/stub-pthreads/README.md

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Implement a stub pthreads library for `THREAD_MODEL=single` (#518) ~~This patch series first starts with a number of commits stubbing out functions in the existing `THREAD_model=posix` code. According to "The Open Group Base Specifications Issue 7, 2018 edition", there are a number of mandatory functions which have not been provided. There are also some optional functions that have been partially provided in a not-useful way (e.g. get but no set function). For these, I have chosen to clean them up and remove the get functions for consistency.~~ EDIT: These have been split off into separate PRs and merged. The remainder of the patches then build up a stub implementation of pthreads for `THREAD_MODEL=single`. I have done my best to try to make sure that all functions are as conforming as possible (under the assumption that another thread cannot ever be launched). This means that objects such as mutexes and rwlocks actually do update their state and will correctly fail when locks cannot be acquired. When an inevitable deadlock occurs, I have chosen to return EDEADLK when it has been explicitly listed as a permissible return value, and to invoke `__builtin_trap` otherwise. I have tested this by rebuilding libc++ with threads enabled and then smoke-testing Clang/LLVM-on-WASI to make sure that it can compile a simple program. I have not run any more-extensive conformance testing. Fixes #501
4 weeks ago
# Single-threaded pthreads stubs
The goal of these files is to provide stub implementations of pthreads
functions for `THREAD_MODEL=single`. This implementation should _always_
follow the strict letter of the POSIX specifications. This means that
"doing nothing", "always succeeding", etc. are not proper implementations
-- these stubs aim for higher conformance than that.
The code that is "more" aligned with the spirit of the POSIX specifications
ends up compiled into libc itself. This primarily consists of synchronization
primitives (which are implemented to actually track state).
The code that is "less" aligned with the spirit of the specifications
(e.g. by "rules-lawyering" and always failing) are built into a library
`wasi-emulated-pthread.a`. The distinction is ultimately made by vibes and a
judgement call, not formal criteria.