Control.Concurrent.STM.TVar

Shared memory locations that support atomic memory transactions.

Create a new TVar holding a value supplied

IO version of newTVar. This is useful for creating top-level TVars using unsafePerformIO, because using atomically inside unsafePerformIO isn't possible.

Return the current value stored in a TVar.

Return the current value stored in a TVar. This is equivalent to

 readTVarIO = atomically . readTVar

but works much faster, because it doesn't perform a complete transaction, it just reads the current value of the TVar.

Write the supplied value into a TVar.

Mutate the contents of a TVar. N.B., this version is non-strict.

Strict version of modifyTVar.

Like modifyTVar' but the function is a simple state transition that can return a side value which is passed on as the result of the STM.

Swap the contents of a TVar for a new value.

Switch the value of returned TVar from initial value False to True after a given number of microseconds. The caveats associated with threadDelay also apply.

Be careful not to exceed maxBound :: Int, which on 32-bit machines is only 2147483647 μs, less than 36 minutes.

Make a Weak pointer to a TVar, using the second argument as a finalizer to run when TVar is garbage-collected