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package faraday
Module FaradaySource
Serialization primitives built for speed an memory-efficiency.
Faraday is a library for writing fast and memory-efficient serializers. Its core type and related operation gives the user fine-grained control over copying and allocation behavior while serializing user-defined types, and presents the output in a form that makes it possible to use vectorized write operations, such as the writev system call, or any other platform or application-specific output APIs.
A Faraday serializer manages an internal buffer and a queue of output buffers. The output bufferes may be a sub range of the serializer's internal buffer or one that is user-provided. Buffered writes such as write_string, write_char, write_bigstring, etc., copy the source bytes into the serializer's internal buffer. Unbuffered writes such as schedule_string, schedule_bigstring, etc., on the other hand perform no copying. Instead, they enqueue the source bytes into the serializer's write queue directly.
The type of a serializer.
Constructors
create len creates a serializer with a fixed-length internal buffer of length len.
of_bigstring buf creates a serializer, using buf as its internal buffer. The serializer takes ownership of buf until the serializer has been closed and flushed of all output.
Buffered Writes
Serializers manage an internal buffer for coalescing small writes. The size of this buffer is determined when the serializer is created and does not change throughout the lifetime of that serializer. If the buffer does not contain sufficient space to service the buffered writes of the caller, a new buffer of the same size will be allocated.
write_string t ?off ?len str copies str into the serializer's internal buffer.
write_bytes t ?off ?len bytes copies bytes into the serializer's internal buffer. It is safe to modify bytes after this call returns.
write_bigstring t ?off ?len bigstring copies bigstring into the serializer's internal buffer. It is safe to modify bytes after this call returns.
Source
val write_gen :
t ->
length:('a -> int) ->
blit:('a -> int -> bigstring -> int -> int -> unit) ->
?off:int ->
?len:int ->
'a ->
unitwrite_gen t ~length ~blit ?off ?len x copies x into the serializer's internal buffer using the provided length and blit operations.
write_char t char copies char into the serializer's internal buffer.
write_uint8 t n copies the lower 8 bits of n into the serializer's internal buffer.
Unbuffered Writes
schedule_string t ?off ?len str schedules str to be written the next time the serializer surfaces writes to the user. str is not copied in this process.
schedule_bytes t ?off ?len bytes schedules bytes to be written the next time the serializer surfaces writes to the user. bytes is not copied in this process, so bytes should only be modified after t has been flushed.
schedule_bigstring t ?free ?off ?len bigstring schedules bigstring to be written the next time the serializer surfaces writes to the user. bigstring is not copied in this process, so bigstring should only be modified after t has been flushed.
Control Operations
yield t causes t to delay surfacing writes to the user, instead returning a `Yield operation with an associated continuation k. This gives the serializer an opportunity to collect additional writes before sending them to the underlying device, which will increase the write batch size. Barring any intervening calls to yield t, calling the continuation k will surface writes to the user.
flush t f registers f to be called when all prior writes have been successfully completed. If t has no pending writes, then f will be called immediately.
close t closes t. All subsequent write calls will raise, and any pending or subsequent yield calls will be ignored. If the serializer has any pending writes, user code will have an opportunity to service them before it receives the Close operation.
is_closed t is true if close has been called on t and false otherwise. A closed t may still have pending output.
shift t n removes the first n bytes in t's write queue. Any scheduled buffers that are contained in this span of bytes are free()'d, if necessary.
drain t removes all pending writes from t, returning the number of bytes that were enqueued to be written and freeing any scheduled buffers in the process.
free_bytes_in_buffer t returns the free space, in bytes, of the serializer's write buffer. If a write_* call has a length that exceeds this value, the serializer will allocate a new buffer that will replace the serializer's internal buffer for that and subsequent calls.
has_pending_output t is true if t's output queue is non-empty. It may be the case that t's queued output is being serviced by some other thread of control, but has not yet completed.
pending_bytes t is the size of the next write, in bytes, that t will surface to the caller.
Running
A view into iovec.buffer starting at iovec.off and with length iovec.len.
Source
type operation = [ | `Writev of buffer iovec list(*Write the ovecs, reporting the actual number of bytes written by calling
*)shift. Failure to do so will result in the same bytes being surfaced in a`Writevoperation multiple times.| `Yield| `Close(*Serialization is complete. No further output will be received.
*)
]serialize t writev sufaces the next operation of t to the caller, handling a `Writev operation with writev function and performing an additional bookkeeping on the caller's behalf. In the event that writev indicates a partial write, serialize will call yield on the serializer rather than attempting successive writev calls.