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Module type File_descr_watcher_intf.S

module type S = sig .. end
type t
A file-descr-watcher is essentially a map from File_descr.t to bool Read_write.t, which defines the set of file descriptors being watched, and for each file descriptor, whether it is being watched for read, write, or both. If a file descriptor is not being watched for neither, it is not in the map.
val invariant : t -> unit
val create : num_file_descrs:int -> t
create ~num_file_descrs creates a new file-descr-watcher that is able to watch file descriptors in 
 [0, num_file_descrs)
.
val set : t ->
       Import.File_descr.t -> bool Read_write.t -> unit
set alters the map of file descriptors being watched. It will take effect on the next call to thread_safe_check. Calling set fd with { read = false, write = false } removes fd from the map.
val iter : t ->
       f:(Import.File_descr.t -> Read_write.Key.t -> unit) -> unit
iter t ~f iterates over every file descriptor in the map, apply f to it once for each of {`Read,`Write} that it is being watched for.
module Pre: sig .. end
pre_check t does whatever non-thread-safe work is necessary to prepare for the system call that checks file descriptors being ready for read or write. 
val pre_check : t -> Pre.t
module Check_result: sig .. end
thread_safe_check t pre ~timeout checks the file descriptors for their status and returns when at least one is available, or the timeout passes. 
val thread_safe_check : t ->
       Pre.t ->
       timeout:File_descr_watcher_intf.Timeout.t ->
       Check_result.t
val post_check : t ->
       Check_result.t ->
       [ `Ok of File_descr_watcher_intf.Post.t Read_write.t
       | `Syscall_interrupted
       | `Timeout ]
post_check t check_result returns the file descriptors available for read and write. Any file descriptor appearing in post for read must have been watched for read, as per set. Similarly for write.
val sexp_of_t : t -> Sexplib.Sexp.t

create ~num_file_descrs creates a new file-descr-watcher that is able to watch file descriptors in 
 [0, num_file_descrs)
.

set alters the map of file descriptors being watched. It will take effect on the next call to thread_safe_check. Calling set fd with { read = false, write = false } removes fd from the map.

iter t ~f iterates over every file descriptor in the map, apply f to it once for each of {`Read,`Write} that it is being watched for.

pre_check t does whatever non-thread-safe work is necessary to prepare for the system call that checks file descriptors being ready for read or write. pre_check does not side effect t.

thread_safe_check t pre ~timeout checks the file descriptors for their status and returns when at least one is available, or the timeout passes. thread_safe_check does not side effect t. Unlike the rest of the functions in this module, thread_safe_check is thread safe.

post_check t check_result returns the file descriptors available for read and write. Any file descriptor appearing in post for read must have been watched for read, as per set. Similarly for write.