GI.GLib.Structs.Once

A Once struct controls a one-time initialization function. Any one-time initialization function must have its own unique Once struct.

Since: 2.4

Exported types

newtype Once

Memory-managed wrapper type.

Constructors

Once (ManagedPtr Once)

Instances

WrappedPtr Once

Defined in GI.GLib.Structs.Once

Methods

wrappedPtrCalloc :: IO (Ptr Once)

wrappedPtrCopy :: Once -> IO Once

wrappedPtrFree :: Maybe (FunPtr (Ptr Once -> IO ()))

tag ~ AttrSet => Constructible Once tag

Defined in GI.GLib.Structs.Once

Methods

new :: MonadIO m => (ManagedPtr Once -> Once) -> [AttrOp Once tag] -> m Once

newZeroOnce :: MonadIO m => m Once

Construct a Once struct initialized to zero.

noOnce :: Maybe Once

A convenience alias for Nothing :: Maybe Once.

Methods

initEnter

onceInitEnter

Arguments

:: (HasCallStack, MonadIO m)

=> Ptr ()

location: location of a static initializable variable containing 0

-> m Bool

Returns: True if the initialization section should be entered, False and blocks otherwise

Function to be called when starting a critical initialization section. The argument location must point to a static 0-initialized variable that will be set to a value other than 0 at the end of the initialization section. In combination with onceInitLeave and the unique address valueLocation, it can be ensured that an initialization section will be executed only once during a program's life time, and that concurrent threads are blocked until initialization completed. To be used in constructs like this:

C code

 static gsize initialization_value = 0;

 if (g_once_init_enter (&initialization_value))
   {
     gsize setup_value = 42; // initialization code here

     g_once_init_leave (&initialization_value, setup_value);
   }

 // use initialization_value here

Since: 2.14

initLeave

onceInitLeave

Arguments

:: (HasCallStack, MonadIO m)

=> Ptr ()

location: location of a static initializable variable containing 0

-> Word64

result: new non-0 value for *valueLocation

-> m ()

Counterpart to onceInitEnter. Expects a location of a static 0-initialized initialization variable, and an initialization value other than 0. Sets the variable to the initialization value, and releases concurrent threads blocking in onceInitEnter on this initialization variable.

Since: 2.14

Properties

retval

the value returned by the call to the function, if status is OnceStatusReady

clearOnceRetval :: MonadIO m => Once -> m ()

Set the value of the “retval” field to Nothing. When overloading is enabled, this is equivalent to

clear #retval

getOnceRetval :: MonadIO m => Once -> m (Ptr ())

Get the value of the “retval” field. When overloading is enabled, this is equivalent to

get once #retval

setOnceRetval :: MonadIO m => Once -> Ptr () -> m ()

Set the value of the “retval” field. When overloading is enabled, this is equivalent to

set once [ #retval := value ]

status

the status of the Once

getOnceStatus :: MonadIO m => Once -> m OnceStatus

Get the value of the “status” field. When overloading is enabled, this is equivalent to

get once #status

setOnceStatus :: MonadIO m => Once -> OnceStatus -> m ()

Set the value of the “status” field. When overloading is enabled, this is equivalent to

set once [ #status := value ]