Database.PostgreSQL.Simple.Queue.Main

This module provides a simple way to create executables for consuming queue payloads. It provides a defaultMain function which takes in a executable name and processing function. It returns a main function which will parse database options on from the command line and spawn a specified number of worker threads.

Here is a simple example that logs out queue payloads

 defaultMain "queue-logger" $ payload count -> do
   print payload
   print count

The worker threads do not attempt to handle exceptions. If an exception is thrown on any threads, all threads are cancel and defaultMain returns. The assumption is the queue executable will get run by a process watcher that can log failures.

For a more complicated example, see the code for the async-email-example documented in EmailQueue.

Options

data PartialOptions

The PartialOptions provide a Monoid for combining options used by defaultMain. The following command line arguments are used to construct a PartialOptions

  --thread-count INT

  Either a connection string
  --connectString ARG
  or individual db properties are provided
  --host STRING
  --port INT
  --user STRING
  --password STRING
  --database STRING

Instances

Eq PartialOptions

Methods

(==) :: PartialOptions -> PartialOptions -> Bool

(/=) :: PartialOptions -> PartialOptions -> Bool

Show PartialOptions

Methods

showsPrec :: Int -> PartialOptions -> ShowS

show :: PartialOptions -> String

showList :: [PartialOptions] -> ShowS

Monoid PartialOptions

Methods

mempty :: PartialOptions

mappend :: PartialOptions -> PartialOptions -> PartialOptions

mconcat :: [PartialOptions] -> PartialOptions

Default PartialOptions

The default threadCount is 1. The default db options are specified in PartialOptions

Methods

def :: PartialOptions

ParseRecord PartialOptions

Methods

parseRecord :: Parser PartialOptions

data Options

Final Options used by run.

Instances

Eq Options

Methods

(==) :: Options -> Options -> Bool

(/=) :: Options -> Options -> Bool

Show Options

Methods

showsPrec :: Int -> Options -> ShowS

show :: Options -> String

showList :: [Options] -> ShowS

completeOptions :: PartialOptions -> Either [String] Options

Convert a PartialOptions to a final Options

Entry Points

defaultMain

Arguments

:: (MonadIO m, MonadBaseControl IO m)

=> Text

Executable name. Used when command line help is printed

-> (Payload -> Int64 -> m ())

Processing function. Takes a Payload to process and the current number of Enqueued Payloads remaining.

-> m ()

This function is a helper for creating queue consumer executables. It takes in a executable name and processing function. It returns a main function which will parse database options on from the command line and spawn a specified number of worker threads. See PartialOptions for command line documentation.

Here is a simple example that logs out queue payloads

 defaultMain "queue-logger" $ payload count -> do
   print payload
   print count

The worker threads do not attempt to handle exceptions. If an exception is thrown on any threads, all threads are cancel and defaultMain returns. The assumption is the queue executable will get run by a process watcher that can log failures.

For a more complicated example, see the code for the async-email-example documented in EmailQueue.

run

Arguments

:: (MonadIO m, MonadBaseControl IO m)

=> (Payload -> Int64 -> m ())

Processing function. Takes a Payload to process and the current number of Enqueued Payloads remaining.

-> Options

Options for thread creation and db connections.

-> m ()

run is called by defaultMain after command line argument parsing is performed. Useful is wants to embed consumer threads inside a larger application.