Data.ByteString.FastBuilder.Internal

This is an internal module; its interface is unstable.

Builder and related types

newtype Builder

Builder is an auxiliary type for efficiently generating a long ByteString. It is isomorphic to lazy ByteString, but offers constant-time concatanation via <>.

Use toLazyByteString to turn a Builder into a ByteString

Constructors

Builder

Fields

unBuilder :: DataSink -> BuilderState -> BuilderState

Instances

IsString Builder

fromString = stringUtf8

Monoid Builder

data BuilderState

This datatype exists only to work around the limitation that oneShot cannot work with unboxed argument types.

Constructors

BuilderState !(Ptr Word8) !(Ptr Word8) (State# RealWorld)

data DataSink

Specifies where bytes generated by a builder go.

Constructors

DynamicSink !(IORef DynamicSink)

The destination of data changes while the builder is running.

GrowingBuffer !(IORef (ForeignPtr Word8))

Bytes are accumulated in a contiguous buffer.

HandleSink !Handle !(IORef Queue)

Bytes are first accumulated in the Queue, then flushed to the Handle.

data DynamicSink

Variable-destination cases.

Constructors

ThreadedSink !(MVar Request) !(MVar Response)

Bytes are sent to another thread.

BoundedGrowingBuffer !(ForeignPtr Word8) !Int

Bytes are accumulated in a contiguous buffer until the size limit is reached. After that, the destination switches to a ThreadedSink.

data Queue

A mutable buffer. The Int specifies where the data start.

Constructors

Queue !(ForeignPtr Word8) !Int

data Request

A request from the driver thread to the builder thread.

Constructors

Request !(Ptr Word8) !(Ptr Word8)

data Response

A response from the builder thread to the driver thread.

Constructors

Error SomeException

A synchronous exception was thrown by the builder

Done !(Ptr Word8)

The builder thread has completed.

MoreBuffer !(Ptr Word8) !Int

The builder thread has finished generating one chunk, and waits for another request with the specified minimum size.

InsertByteString !(Ptr Word8) !ByteString

The builder thread has partially filled the current chunk, and wants to emit the bytestring to be included in the final output.

Instances

Show Response

Internally used exceptions

data SuspendBuilderException

Used in the implementation of toLazyByteString. This is a message sent from the consumer thread to the builder thread, requesting the builder thread to temporarily pause execution. Later, the consumer thread may request resumption by filling the MVar.

Constructors

SuspendBuilderException !(MVar ())

Instances

Show SuspendBuilderException

Exception SuspendBuilderException

data ChunkOverflowException

Used in the implementation of toLazyByteString. This is an exception thrown by the consumer thread to itself when it has finished filling the first chunk of the output. After this, a thread will be forked, and the execution of the builder will be resumed in the new thread, using ThreadedSink.

Constructors

ChunkOverflowException !ByteString !(MVar Request) !(MVar Response) !Int

Instances

Show ChunkOverflowException

Exception ChunkOverflowException

Builder building blocks

type Builder_ = DataSink -> Addr# -> Addr# -> State# RealWorld -> (#Addr#, Addr#, State# RealWorld#)

An internal type that is isomorphic to Builder. This is a maximaly efficient representation for NOINLINE functions.

newtype BuildM a

An internal type for making it easier to define builders. A value of BuildM a can do everything a Builder can do, and in addition, returns a value of type a upon completion.

Constructors

BuildM

Fields

runBuildM :: (a -> Builder) -> Builder

Instances

Monad BuildM

Functor BuildM

Applicative BuildM

toBuilder_ :: Builder -> Builder_

Convert a Builder into a Builder_.

fromBuilder_ :: Builder_ -> Builder

Convert a Builder_ into a Builder.

mkBuilder :: BuildM () -> Builder

Create a builder from a BuildM.

useBuilder :: Builder -> BuildM ()

Embed a builder in the BuildM context.

getSink :: BuildM DataSink

Get the DataSink.

getCur :: BuildM (Ptr Word8)

Get the current pointer.

getEnd :: BuildM (Ptr Word8)

Get the end-of-buffer pointer.

setCur :: Ptr Word8 -> BuildM ()

Set the current pointer.

setEnd :: Ptr Word8 -> BuildM ()

Set the end-of-buffer pointer.

Running builders

runBuilder :: Builder -> DataSink -> Ptr Word8 -> Ptr Word8 -> IO (Ptr Word8)

Run a builder.

toLazyByteString :: Builder -> ByteString

Turn a Builder into a lazy ByteString.

Performance hint: when the resulting ByteString does not fit in one chunk, this function forks a thread. Due to this, the performance degrades sharply if you use this function from a bound thread. Note in particular that the main thread is a bound thread when you use ghc -threaded.

To avoid this problem, do one of these:

• Make sure the resulting ByteString is consumed in an unbound thread. Consider using runInUnboundThread for this.
• Use other function to run the Builder instead. Functions that don't return a lazy ByteString do not have this issue.
• Link your program without -threaded.

toLazyByteStringWith :: Int -> Int -> Builder -> ByteString

Like toLazyByteString, but allows the user to specify the initial and the subsequent desired buffer sizes.

toStrictByteString :: Builder -> ByteString

Turn a Builder into a strict ByteString.

hPutBuilder :: Handle -> Builder -> IO ()

Output a Builder to a Handle.

Basic builders

primBounded :: BoundedPrim a -> a -> Builder

Turn a value of type a into a Builder, using the given BoundedPrim.

primFixed :: FixedPrim a -> a -> Builder

Turn a value of type a into a Builder, using the given FixedPrim.

primMapListBounded :: BoundedPrim a -> [a] -> Builder

Turn a list of values of type a into a Builder, using the given BoundedPrim.

primMapListFixed :: FixedPrim a -> [a] -> Builder

Turn a list of values of type a into a Builder, using the given FixedPrim.

byteString :: ByteString -> Builder

Turn a ByteString to a Builder.

byteStringThreshold :: Int -> ByteString -> Builder

Turn a ByteString to a Builder. If the size of the ByteString is larger than the given threshold, avoid copying it as much as possible.

byteStringCopy :: ByteString -> Builder

Turn a ByteString to a Builder. The ByteString will be copied to the buffer, regardless of the size.

byteStringCopyNoCheck :: ByteString -> Builder

Like byteStringCopy, but assumes that the current buffer is large enough.

byteStringInsert :: ByteString -> Builder

Turn a ByteString to a Builder. When possible, the given ByteString will not be copied, and inserted directly into the output instead.

unsafeCString :: CString -> Builder

Turn a C String into a Builder. The behavior is undefined if the given CString does not point to a constant null-terminated string.

ensureBytes :: Int -> Builder

ensureBytes n ensures that at least n bytes of free space is available in the current buffer, by allocating a new buffer when necessary.

getBytes :: Int -> Builder

getBytes n allocates a new buffer, containing at least n bytes.

Performance tuning

rebuild :: Builder -> Builder

rebuild b is equivalent to b, but it allows GHC to assume that b will be run at most once. This can enable various optimizations that greately improve performance.

There are two types of typical situations where a use of rebuild is often a win:

• When constructing a builder using a recursive function. e.g. rebuild $ foldr ....
• When constructing a builder using a conditional expression. e.g. rebuild $ case x of ...