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The Thread_safe module has functions that are safe to call from threads outside Async, such as the ones spawned by In_thread.run.
This is in contrast with the rest of Async library which is generally not thread-safe.
All the Thread_safe.block* and Thread_safe.run* functions wake up the Async scheduler to ensure that it continues in a timely manner with whatever jobs got started. Some functions take an optional ?wakeup_scheduler:bool argument, which defaults to true. One can cause the scheduler to not be woken up by supplying ~wakeup_scheduler:false, which can reduce CPU use, but increase latency, because the scheduler may not wake up for a while to process jobs.
val am_holding_async_lock : unit -> bool
am_holding_async_lock () returns true if the currently running thread is holding the Async lock.
run_in_async_with_optional_cycle f acquires the Async lock and runs f () while holding the lock. Depending on the result of f, it may also run a cycle.
val run_in_async :
?wakeup_scheduler:bool ->(unit ->'a)->('a, exn)Core.Result.t
run_in_async f acquires the Async lock and runs f () while holding the lock. It returns the result of f () to the outside world. The scheduler is woken up to ensure the code that depends on f () is run soon enough.
run_in_async doesn't run a cycle.
run_in_async does not automatically start the Async scheduler. You still need to call Scheduler.go elsewhere in your program.
val run_in_async_exn : ?wakeup_scheduler:bool ->(unit ->'a)->'a
block_on_async f runs f () in the Async world and blocks until the result becomes determined. This function can be called from the main thread (before Async is started) or from a thread outside Async.
block_on_async will run a cycle if the deferred isn't determined, in the hope that running the cycle will cause the deferred to become determined.
block_on_async will automatically start the scheduler if it isn't already running.
run_in_async_wait f is like block_on_async f, except that it must be called from a thread outside Async. Upon returning from run_in_async_wait, it is guaranteed that the caller does not have the Async lock.
without_async_lock f can not be called from async, usually because f is expected to block. It's safe to call it in these two circumstances:
from a separate thread that's not holding the async lock
from the main thread, even if it is holding the async lock, as long as it's not running async jobs. In the latter case the async lock is dropped for the duration of f.