Module Async_unix.Scheduler

t () returns the Async scheduler. If the scheduler hasn't been created yet, this will create it and acquire the Async lock.

go ?raise_unhandled_exn () passes control to Async, at which point Async starts running handlers, one by one without interruption, until there are no more handlers to run. When Async is out of handlers, it blocks until the outside world schedules more of them. Because of this, Async programs do not exit until shutdown is called.

go () calls handle_signal Sys.sigpipe, which causes the SIGPIPE signal to be ignored. Low-level syscalls (e.g., write) still raise EPIPE.

If any Async job raises an unhandled exception that is not handled by any monitor, Async execution ceases. Then, by default, Async pretty prints the exception, and exits with status 1. If you don't want this, pass ~raise_unhandled_exn:true, which will cause the unhandled exception to be raised to the caller of go ().

go_main is like go, except that you supply a main function that will be run to initialize the Async computation, and that go_main will fail if any Async has been used prior to go_main being called. Moreover it allows you to configure more static options of the scheduler.

report_long_cycle_times ?cutoff () sets up something that will print a warning to stderr whenever there is an Async cycle that is too long, as specified by cutoff, whose default is 1s.

is_running () returns true if the scheduler has been started.

set_max_inter_cycle_timeout span sets the maximum amount of time the scheduler will remain blocked (on epoll or select) between cycles.

set_check_invariants do_check sets whether Async should check invariants of its internal data structures. set_check_invariants true can substantially slow down your program.

set_detect_invalid_access_from_thread do_check sets whether Async routines should check if they are being accessed from some thread other than the thread currently holding the Async lock, which is not allowed and can lead to very confusing behavior.

fold_fields ~init folder folds folder over each field in the scheduler. The fields themselves are not exposed -- folder must be a polymorphic function that can work on any field. So, it's only useful for generic operations, e.g., getting the size of each field.

If a process that has already created, but not started, the Async scheduler would like to fork, and would like the child to have a clean Async, i.e., not inherit any of the Async work that was done in the parent, it can call reset_in_forked_process at the start of execution in the child process. After that, the child can do Async stuff and then start the Async scheduler.

make_async_unusable () makes subsequent attempts to use the Async scheduler raise. One use case for make_async_unusable is if you fork from a process already running the Async scheduler, and want to run non-Async OCaml code in the child process, with the guarantee that the child process does not use Async.

Async supports "busy polling", which runs a thread that busy loops running user-supplied polling functions. The busy-loop thread is distinct from Async's scheduler thread.

Busy polling is useful for a situation like a shared-memory ringbuffer being used for IPC. One can poll the ringbuffer with a busy poller, and then when data is detected, fill some ivar that causes Async code to handle the data.

add_busy_poller poll adds poll to the busy loop. poll will be called continuously, once per iteration of the busy loop, until it returns `Stop_polling a at which point the result of add_busy_poller will become determined. poll will hold the Async lock while running, so it is fine to do ordinary Async operations, e.g., fill an ivar. The busy loop will run an ordinary Async cycle if any of the pollers add jobs.

poll will run in the monitor in effect when add_busy_poller was called; exceptions raised by poll will be sent asynchronously to that monitor. If poll raises, it will still be run on subsequent iterations of the busy loop.

handle_thread_pool_stuck f causes f to run whenever Async detects its thread pool is stuck (i.e., hasn't completed a job for over a second and has work waiting to start). Async checks every second. By default, if the thread pool has been stuck for less than 60s, Async will eprintf a message. If more than 60s, Async will send an exception to the main monitor, which will abort the program unless there is a custom handler for the main monitor.

Calling handle_thread_pool_stuck replaces whatever behavior was previously there.

time_spent_waiting_for_io () returns the amount of time that the Async scheduler has spent in calls to epoll_wait (or select) since the start of the program.

set_min_inter_cycle_timeout sets the minimum timeout that the scheduler will pass to the OS when it checks for I/O between cycles. The minimum is zero by default. Setting it to a nonzero value is used to increase thread fairness between the scheduler and other threads. A plausible setting is 10us. This can also be set via the ASYNC_CONFIG environment variable.