Takes an IO action that will be executed iff the transaction commits.
- When a TVar was modified in a transaction and this transaction commits,
this update remains invisible to other threads until the corresponding
onCommit action was run.
- If the onCommit action throws an exception, the original value of
the TVars will be restored.
- Accessing a modified TVar within the onCommit action will cause a
Deadlock exception to be thrown.
As a general rule, onCommit should
only be used for "real" (i.e. without atomic blocks) IO actions and is certainly
not the right place to fiddle with TVars. For example, if you wanted to
write a TVar value to a file on commit, you could write:
tvar <- newTVarIO "bla"
atomically $ do
x <- readTVar tvar
onCommit (writeFile "myfile" x)
|:: IO ()||IO action that will be run if the transaction is (explicitly) retried.
|-> m ()|
Adds an IO action to the retry job-queue. If the transaction retries,
a new helper thread is forked that runs the retry actions, and, after the helper
thread is done, the transaction retries.
Note: When the transaction is retried, unsafeIOToSTM is used to fork a
helper thread that runs the retry actions (if any). It is your
responsibility to ensure that your retry IO-actions are `safe'. Any
exceptions occurring in the retry-thread will be thrown to the
thread where the transaction is running and immediately cause the transaction to be
aborted, since catchSTM does not catch asynchronous exceptions.
|orElse :: m a -> m a -> m a||Source|
|Runs any IO actions added by onRetry and then retries the
|Lifts STM actions to MonadAdvSTM.
|Reads a value from a TVar. Blocks until the IO onCommit action(s) of
the corresponding transaction are complete.
See onCommit for a more detailed description of this behaviour.
|Writes a value to a TVar. Blocks until the onCommit IO-action(s) are
complete. See onCommit for details.