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Fix a few typos in the threading doc.

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NullCascade 2018-06-30 10:14:50 -07:00 committed by ThePhD
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docs/source/threading.rst
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threading threading
========= =========
Lua has no thread safety. sol does not force thread safety bottlenecks anywhere. Tr(eat access and object handling like you were dealing with a raw ``int`` reference (``int&``) (no safety or order guarantees whatsoever). Lua has no thread safety. sol does not force thread safety bottlenecks anywhere. Treat access and object handling like you were dealing with a raw ``int`` reference (``int&``) (no safety or order guarantees whatsoever).
Assume any access or any call on Lua affects the whole ``sol::state``/``lua_State*`` (because it does, in a fair bit of cases). Therefore, every call to a state should be blocked off in C++ with some kind of access control (when you're working with multiple C++ threads). When you start hitting the same state from multiple threads, race conditions (data or instruction) can happen. Assume any access or any call on Lua affects the whole ``sol::state``/``lua_State*`` (because it does, in a fair bit of cases). Therefore, every call to a state should be blocked off in C++ with some kind of access control (when you're working with multiple C++ threads). When you start hitting the same state from multiple threads, race conditions (data or instruction) can happen.
Individual Lua coroutines might be able to run on separate C++-created threads without tanking the state utterly, since each Lua coroutine has the capability to run on an independent Lua execution stack (Lua confusingly calls it a ``thread`` in the C API, but it really just means a seperate execution stack) as well as some other associated bits and pieces that won't quite interfere with the global state. Individual Lua coroutines might be able to run on separate C++-created threads without tanking the state utterly, since each Lua coroutine has the capability to run on an independent Lua execution stack (Lua confusingly calls it a ``thread`` in the C API, but it really just means a separate execution stack) as well as some other associated bits and pieces that won't quite interfere with the global state.
To handle multithreaded environments, it is encouraged to either spawn a Lua state (``sol::state``) for each thread you are working with and keep inter-state communication to synchronized serialization points. This means that 3 C++ threads should each have their own Lua state, and access between them should be controlled using some kind of synchronied C++ mechanism (actual transfer between states must be done by serializing the value into C++ and then re-pushing it into the other state). To handle multithreaded environments, it is encouraged to either spawn a Lua state (``sol::state``) for each thread you are working with and keep inter-state communication to synchronized serialization points. This means that 3 C++ threads should each have their own Lua state, and access between them should be controlled using some kind of synchronized C++ mechanism (actual transfer between states must be done by serializing the value into C++ and then re-pushing it into the other state).
Using coroutines and Lua's threads might also buy you some concurrency and parallelism (**unconfirmed and likely untrue, do not gamble on this**), but remember that Lua's 'threading' technique is ultimately cooperative and requires explicit yielding and resuming (simplified as function calls for :doc:`sol::coroutine<api/coroutine>`). Using coroutines and Lua's threads might also buy you some concurrency and parallelism (**unconfirmed and likely untrue, do not gamble on this**), but remember that Lua's 'threading' technique is ultimately cooperative and requires explicit yielding and resuming (simplified as function calls for :doc:`sol::coroutine<api/coroutine>`).