System.Linux.EventFD

(source)

This provides wrappers around the `sys/eventfd.h` module: An "event"
file descriptort that can be monitored via `epoll` and written to
programmatically to wake up a dormant thread.

The file descriptor can work in `EFD_SEMAPHORE` mode, in which case it
can indeed be used liked a `System.Concurrent.Semaphore` or a
`System.Concurrent.Condition`.

Definitions

record Flags : Type

  Flags describing the behavior of an event file descriptor.
  
  Several flags can be combined using `(<+>)`.

Totality: total
Visibility: export
Constructor:

F : Bits32 -> Flags

Projection:

.value : Flags -> Bits32

Hints:

Eq Flags
Monoid Flags
Ord Flags
Semigroup Flags
Show Flags

flagCode : Flags -> Bits32

Totality: total
Visibility: export

EFD_CLOEXEC : Flags

Totality: total
Visibility: export

EFD_NONBLOCK : Flags

  Sets the file descriptor to non-blocking: Reading from
  an `EventFD` via `readEv` will usually block the calling thread
  unless the file descriptor's stored value is greater than zero.
  
  With this flag being set, `readEv` will never block but will return
  `Left EAGAIN` in case of an empty file descriptor.

Totality: total
Visibility: export

EFD_SEMAPHORE : Flags

  Changes the file descriptor to work in "semaphore mode": Usually,
  `readEv` will return the whole 64-bit value currently stored in the
  file descriptor. In semaphore mode, `readEv` will always return 1
  (unliss the file descriptor is empty) and likewise reduce the stored
  value by 1.

Totality: total
Visibility: export

record EventFD : Type

  An event file descriptor that can be monitored via `epoll`
  and programmatically written to and read from.

Totality: total
Visibility: public export
Constructor:

EFD : Bits32 -> EventFD

Projection:

.file : EventFD -> Bits32

Hint:

FileDesc EventFD

.file : EventFD -> Bits32

Totality: total
Visibility: public export

file : EventFD -> Bits32

Totality: total
Visibility: public export

eventfd : Bits64 -> Flags -> PrimIO EventFD

  Creates a new `EventFD` with the given initial value a flags set.

Totality: total
Visibility: export

writeEv : EventFD -> Bits64 -> PrimIO ()

  Writes (adds) the given 64-bit value to the value currently stored
  in the given event file descriptor.

Totality: total
Visibility: export

readEv : EventFD -> PrimIO (Either EpollErr Bits64)

  Reads the current value from an event file descriptor, setting the
  stored value to 0.
  
  If the `EFD_SEMAPHORE` flag was set when creating the file descriptor,
  this will always return 1 in case the event file is non-empty. Likewise,
  the value stored in the event file will be reduced by one.

Totality: total
Visibility: export

withEv : Bits64 -> Flags -> (EventFD -> PrimIO a) -> PrimIO a

  Creates and finally closes and event file descriptor.

Totality: total
Visibility: export