System.Console.Concurrent.Internal

Concurrent output handling, internals.

May change at any time.

Documentation

data OutputHandle

Constructors

OutputHandle

Fields

outputLock :: TMVar Lock

outputBuffer :: TMVar OutputBuffer

errorBuffer :: TMVar OutputBuffer

outputThreads :: TMVar Integer

processWaiters :: TMVar [Async ()]

waitForProcessLock :: TMVar ()

data Lock

Constructors

Locked

globalOutputHandle :: OutputHandle

A shared global variable for the OutputHandle.

lockOutput :: (MonadIO m, MonadMask m) => m a -> m a

Holds a lock while performing an action. This allows the action to perform its own output to the console, without using functions from this module.

While this is running, other threads that try to lockOutput will block. Any calls to outputConcurrent and createProcessConcurrent will not block, but the output will be buffered and displayed only once the action is done.

takeOutputLock :: IO ()

Blocks until we have the output lock.

tryTakeOutputLock :: IO Bool

Tries to take the output lock, without blocking.

withLock :: (TMVar Lock -> STM a) -> IO a

takeOutputLock' :: Bool -> IO Bool

dropOutputLock :: IO ()

Only safe to call after taking the output lock.

withConcurrentOutput :: (MonadIO m, MonadMask m) => m a -> m a

Use this around any actions that use outputConcurrent or createProcessConcurrent

This is necessary to ensure that buffered concurrent output actually gets displayed before the program exits.

flushConcurrentOutput :: IO ()

Blocks until any processes started by createProcessConcurrent have finished, and any buffered output is displayed.

withConcurrentOutput calls this at the end; you can call it anytime you want to flush output.

class Outputable v where

Values that can be output.

Methods

toOutput :: v -> Text

Instances

Outputable String

Outputable Text

outputConcurrent :: Outputable v => v -> IO ()

Displays a value to stdout.

No newline is appended to the value, so if you want a newline, be sure to include it yourself.

Uses locking to ensure that the whole output occurs atomically even when other threads are concurrently generating output.

When something else is writing to the console at the same time, this does not block. It buffers the value, so it will be displayed once the other writer is done.

errorConcurrent :: Outputable v => v -> IO ()

Like outputConcurrent, but displays to stderr.

(Does not throw an exception.)

outputConcurrent' :: Outputable v => StdHandle -> v -> IO ()

newtype ConcurrentProcessHandle

Constructors

ConcurrentProcessHandle ProcessHandle

toConcurrentProcessHandle :: (Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle) -> (Maybe Handle, Maybe Handle, Maybe Handle, ConcurrentProcessHandle)

waitForProcessConcurrent :: ConcurrentProcessHandle -> IO ExitCode

Use this to wait for processes started with createProcessConcurrent and createProcessForeground, and get their exit status.

Note that such processes are actually automatically waited for internally, so not calling this explicitly will not result in zombie processes. This behavior differs from waitForProcess

asyncProcessWaiter :: IO () -> IO ()

createProcessConcurrent :: CreateProcess -> IO (Maybe Handle, Maybe Handle, Maybe Handle, ConcurrentProcessHandle)

Wrapper around createProcess that prevents multiple processes that are running concurrently from writing to stdout/stderr at the same time.

If the process does not output to stdout or stderr, it's run by createProcess entirely as usual. Only processes that can generate output are handled specially:

A process is allowed to write to stdout and stderr in the usual way, assuming it can successfully take the output lock.

When the output lock is held (ie, by another concurrent process, or because outputConcurrent is being called at the same time), the process is instead run with its stdout and stderr redirected to a buffer. The buffered output will be displayed as soon as the output lock becomes free.

Currently only available on Unix systems, not Windows.

createProcessForeground :: CreateProcess -> IO (Maybe Handle, Maybe Handle, Maybe Handle, ConcurrentProcessHandle)

Wrapper around createProcess that makes sure a process is run in the foreground, with direct access to stdout and stderr. Useful when eg, running an interactive process.

fgProcess :: CreateProcess -> IO (Maybe Handle, Maybe Handle, Maybe Handle, ConcurrentProcessHandle)

bgProcess :: CreateProcess -> IO (Maybe Handle, Maybe Handle, Maybe Handle, ConcurrentProcessHandle)

willOutput :: StdStream -> Bool

data OutputBuffer

Buffered output.

Constructors

OutputBuffer [OutputBufferedActivity]

Instances

Eq OutputBuffer

data StdHandle

Constructors

StdOut

StdErr

toHandle :: StdHandle -> Handle

bufferFor :: StdHandle -> TMVar OutputBuffer

data OutputBufferedActivity

Constructors

Output Text

InTempFile

Fields

tempFile :: FilePath

endsInNewLine :: Bool

Instances

Eq OutputBufferedActivity

data AtEnd

Constructors

AtEnd

Instances

Eq AtEnd

data BufSig

Constructors

BufSig

setupOutputBuffer :: StdHandle -> Handle -> StdStream -> Handle -> IO (StdHandle, MVar OutputBuffer, TMVar BufSig, TMVar AtEnd)

outputDrainer :: StdStream -> Handle -> MVar OutputBuffer -> TMVar BufSig -> TMVar AtEnd -> IO ()

registerOutputThread :: IO ()

unregisterOutputThread :: IO ()

bufferWriter :: [(StdHandle, MVar OutputBuffer, TMVar BufSig, TMVar AtEnd)] -> IO ()

addOutputBuffer :: OutputBufferedActivity -> OutputBuffer -> IO OutputBuffer

bufferOutputSTM :: Outputable v => StdHandle -> v -> STM ()

Adds a value to the output buffer for later display.

Note that buffering large quantities of data this way will keep it resident in memory until it can be displayed. While outputConcurrent uses temp files if the buffer gets too big, this STM function cannot do so.

bufferOutputSTM' :: StdHandle -> OutputBuffer -> STM ()

outputBufferWaiterSTM :: (OutputBuffer -> (OutputBuffer, OutputBuffer)) -> STM (StdHandle, OutputBuffer)

A STM action that waits for some buffered output to become available, and returns it.

The function can select a subset of output when only some is desired; the fst part is returned and the snd is left in the buffer.

This will prevent it from being displayed in the usual way, so you'll need to use emitOutputBuffer to display it yourself.

waitAnyBuffer :: OutputBuffer -> (OutputBuffer, OutputBuffer)

waitCompleteLines :: OutputBuffer -> (OutputBuffer, OutputBuffer)

Use with outputBufferWaiterSTM to make it only return buffered output that ends with a newline. Anything buffered without a newline is left in the buffer.

endsNewLine :: Text -> Bool

emitOutputBuffer :: StdHandle -> OutputBuffer -> IO ()

Emits the content of the OutputBuffer to the Handle

If you use this, you should use lockOutput to ensure you're the only thread writing to the console.