Input / output¶

Interfaces¶

class arrow::io::FileInterface¶

Subclassed by arrow::io::InputStream, arrow::io::OutputStream

Public Functions

Status Close() = 0¶

Close the stream cleanly.

For writable streams, this will attempt to flush any pending data before releasing the underlying resource.

After Close() is called, closed() returns true and the stream is not available for further operations.

Status Abort()¶

Close the stream abruptly.

This method does not guarantee that any pending data is flushed. It merely releases any underlying resource used by the stream for its operation.

After Abort() is called, closed() returns true and the stream is not available for further operations.

Result<int64_t> Tell() const = 0¶: Return the position in this stream.

bool closed() const = 0¶: Return whether the stream is closed.

class arrow::io::Readable¶

Subclassed by arrow::io::InputStream

Public Functions

Result<int64_t> Read(int64_t nbytes, void *out) = 0¶

Read data from current file position.

Read at most nbytes from the current file position into out. The number of bytes read is returned.

Result<std::shared_ptr<Buffer>> Read(int64_t nbytes) = 0¶

Read data from current file position.

Read at most nbytes from the current file position. Less bytes may be read if EOF is reached. This method updates the current file position.

In some cases (e.g. a memory-mapped file), this method may avoid a memory copy.

class Seekable¶: Subclassed by arrow::io::RandomAccessFile, arrow::io::WritableFile

class arrow::io::Writable¶

Subclassed by arrow::io::OutputStream

Public Functions

Status Write(const void *data, int64_t nbytes) = 0¶

Write the given data to the stream.

This method always processes the bytes in full. Depending on the semantics of the stream, the data may be written out immediately, held in a buffer, or written asynchronously. In the case where the stream buffers the data, it will be copied. To avoid potentially large copies, use the Write variant that takes an owned Buffer.

Status Write(const std::shared_ptr<Buffer> &data)¶

Write the given data to the stream.

Since the Buffer owns its memory, this method can avoid a copy if buffering is required. See Write(const void*, int64_t) for details.

Status Flush()¶: Flush buffered bytes, if any.

class arrow::io::InputStream : public virtual arrow::io::FileInterface, public virtual arrow::io::Readable ¶

Subclassed by arrow::io::internal::InputStreamConcurrencyWrapper< Derived >, arrow::io::RandomAccessFile, arrow::io::StdinStream, arrow::io::TransformInputStream, arrow::io::internal::InputStreamConcurrencyWrapper< BufferedInputStream >, arrow::io::internal::InputStreamConcurrencyWrapper< CompressedInputStream >, arrow::io::SlowInputStreamBase< InputStream >

Public Functions

Status Advance(int64_t nbytes)¶

Advance or skip stream indicated number of bytes.

Return

Status

Parameters

[in] nbytes: the number to move forward

Result<util::string_view> Peek(int64_t nbytes)¶

Return zero-copy string_view to upcoming bytes.

Do not modify the stream position. The view becomes invalid after any operation on the stream. May trigger buffering if the requested size is larger than the number of buffered bytes.

May return NotImplemented on streams that don’t support it.

Parameters

[in] nbytes: the maximum number of bytes to see

bool supports_zero_copy() const¶

Return true if InputStream is capable of zero copy Buffer reads.

Zero copy reads imply the use of Buffer-returning Read() overloads.

class arrow::io::RandomAccessFile : public std::enable_shared_from_this<RandomAccessFile>, public arrow::io::InputStream, public arrow::io::Seekable ¶

Subclassed by arrow::io::HdfsReadableFile, arrow::io::internal::RandomAccessFileConcurrencyWrapper< Derived >, arrow::io::ReadWriteFileInterface, arrow::py::PyReadableFile, parquet::ParquetInputWrapper, arrow::io::internal::RandomAccessFileConcurrencyWrapper< BufferReader >, arrow::io::internal::RandomAccessFileConcurrencyWrapper< CudaBufferReader >, arrow::io::internal::RandomAccessFileConcurrencyWrapper< ReadableFile >, arrow::io::SlowInputStreamBase< RandomAccessFile >

Public Functions

~RandomAccessFile() override¶: Necessary because we hold a std::unique_ptr.

Result<int64_t> GetSize() = 0¶

Return the total file size in bytes.

This method does not read or move the current file position, so is safe to call concurrently with e.g. ReadAt().

Result<int64_t> ReadAt(int64_t position, int64_t nbytes, void *out)¶

Read data from given file position.

At most nbytes bytes are read. The number of bytes read is returned (it can be less than nbytes if EOF is reached).

This method can be safely called from multiple threads concurrently. It is unspecified whether this method updates the file position or not.

The default RandomAccessFile-provided implementation uses Seek() and Read(), but subclasses may override it with a more efficient implementation that doesn’t depend on implicit file positioning.

Return

The number of bytes read, or an error

Parameters

[in] position: Where to read bytes from
[in] nbytes: The number of bytes to read
[out] out: The buffer to read bytes into

Result<std::shared_ptr<Buffer>> ReadAt(int64_t position, int64_t nbytes)¶

Read data from given file position.

At most nbytes bytes are read, but it can be less if EOF is reached.

Return

A buffer containing the bytes read, or an error

Parameters

[in] position: Where to read bytes from
[in] nbytes: The number of bytes to read

Future<std::shared_ptr<Buffer>> ReadAsync(const AsyncContext&, int64_t position, int64_t nbytes)¶: EXPERIMENTAL: Read data asynchronously.

Status WillNeed(const std::vector<ReadRange> &ranges)¶

EXPERIMENTAL: Inform that the given ranges may be read soon.

Some implementations might arrange to prefetch some of the data. However, no guarantee is made and the default implementation does nothing. For robust prefetching, use ReadAt() or ReadAsync().

Public Static Functions

std::shared_ptr<InputStream> GetStream(std::shared_ptr<RandomAccessFile> file, int64_t file_offset, int64_t nbytes)¶

Create an isolated InputStream that reads a segment of a RandomAccessFile.

Multiple such stream can be created and used independently without interference

Parameters

[in] file: a file instance
[in] file_offset: the starting position in the file
[in] nbytes: the extent of bytes to read. The file should have sufficient bytes available

class OutputStream : public virtual arrow::io::FileInterface, public arrow::io::Writable ¶: Subclassed by arrow::io::BufferedOutputStream, arrow::io::BufferOutputStream, arrow::io::CompressedOutputStream, arrow::io::FileOutputStream, arrow::io::HdfsOutputStream, arrow::io::MockOutputStream, arrow::io::StderrStream, arrow::io::StdoutStream, arrow::io::WritableFile, arrow::py::PyOutputStream, parquet::ParquetOutputWrapper

class ReadWriteFileInterface : public arrow::io::RandomAccessFile, public arrow::io::WritableFile¶: Subclassed by arrow::io::MemoryMappedFile

Concrete implementations¶

In-memory streams¶

class arrow::io::BufferReader : public arrow::io::internal::RandomAccessFileConcurrencyWrapper<BufferReader>¶

Random access zero-copy reads on an arrow::Buffer.

Public Functions

BufferReader(const util::string_view &data)¶

Instantiate from std::string or arrow::util::string_view.

Does not own data

bool closed() const override¶: Return whether the stream is closed.

bool supports_zero_copy() const override¶

Return true if InputStream is capable of zero copy Buffer reads.

Zero copy reads imply the use of Buffer-returning Read() overloads.

Future<std::shared_ptr<Buffer>> ReadAsync(const AsyncContext&, int64_t position, int64_t nbytes) override¶: EXPERIMENTAL: Read data asynchronously.

Status WillNeed(const std::vector<ReadRange> &ranges) override¶

EXPERIMENTAL: Inform that the given ranges may be read soon.

Some implementations might arrange to prefetch some of the data. However, no guarantee is made and the default implementation does nothing. For robust prefetching, use ReadAt() or ReadAsync().

class arrow::io::MockOutputStream : public arrow::io::OutputStream ¶

A helper class to tracks the size of allocations.

Writes to this stream do not copy or retain any data, they just bump a size counter that can be later used to know exactly which data size needs to be allocated for actual writing.

Public Functions

Status Close() override¶

Close the stream cleanly.

For writable streams, this will attempt to flush any pending data before releasing the underlying resource.

After Close() is called, closed() returns true and the stream is not available for further operations.

bool closed() const override¶: Return whether the stream is closed.

Result<int64_t> Tell() const override¶: Return the position in this stream.

Status Write(const void *data, int64_t nbytes) override¶

Write the given data to the stream.

This method always processes the bytes in full. Depending on the semantics of the stream, the data may be written out immediately, held in a buffer, or written asynchronously. In the case where the stream buffers the data, it will be copied. To avoid potentially large copies, use the Write variant that takes an owned Buffer.

class arrow::io::BufferOutputStream : public arrow::io::OutputStream ¶

An output stream that writes to a resizable buffer.

Public Functions

Status Close() override¶: Close the stream, preserving the buffer (retrieve it with Finish()).

bool closed() const override¶: Return whether the stream is closed.

Result<int64_t> Tell() const override¶: Return the position in this stream.

Status Write(const void *data, int64_t nbytes) override¶

Write the given data to the stream.

This method always processes the bytes in full. Depending on the semantics of the stream, the data may be written out immediately, held in a buffer, or written asynchronously. In the case where the stream buffers the data, it will be copied. To avoid potentially large copies, use the Write variant that takes an owned Buffer.

Result<std::shared_ptr<Buffer>> Finish()¶: Close the stream and return the buffer.

Status Reset(int64_t initial_capacity = 1024, MemoryPool *pool = default_memory_pool())¶

Initialize state of OutputStream with newly allocated memory and set position to 0.

Return

Status

Parameters

[in] initial_capacity: the starting allocated capacity
[inout] pool: the memory pool to use for allocations

Public Static Functions

Result<std::shared_ptr<BufferOutputStream>> Create(int64_t initial_capacity = 4096, MemoryPool *pool = default_memory_pool())¶

Create in-memory output stream with indicated capacity using a memory pool.

Return

the created stream

Parameters

[in] initial_capacity: the initial allocated internal capacity of the OutputStream
[inout] pool: a MemoryPool to use for allocations

class arrow::io::FixedSizeBufferWriter : public arrow::io::WritableFile¶

An output stream that writes into a fixed-size mutable buffer.

Public Functions

FixedSizeBufferWriter(const std::shared_ptr<Buffer> &buffer)¶: Input buffer must be mutable, will abort if not.

Status Close() override¶

Close the stream cleanly.

For writable streams, this will attempt to flush any pending data before releasing the underlying resource.

After Close() is called, closed() returns true and the stream is not available for further operations.

bool closed() const override¶: Return whether the stream is closed.

Result<int64_t> Tell() const override¶: Return the position in this stream.

Status Write(const void *data, int64_t nbytes) override¶

Write the given data to the stream.

This method always processes the bytes in full. Depending on the semantics of the stream, the data may be written out immediately, held in a buffer, or written asynchronously. In the case where the stream buffers the data, it will be copied. To avoid potentially large copies, use the Write variant that takes an owned Buffer.

Local files¶

class arrow::io::ReadableFile : public arrow::io::internal::RandomAccessFileConcurrencyWrapper<ReadableFile>¶

An operating system file open in read-only mode.

Reads through this implementation are unbuffered. If many small reads need to be issued, it is recommended to use a buffering layer for good performance.

Public Functions

bool closed() const override¶: Return whether the stream is closed.

Status WillNeed(const std::vector<ReadRange> &ranges) override¶

EXPERIMENTAL: Inform that the given ranges may be read soon.

Some implementations might arrange to prefetch some of the data. However, no guarantee is made and the default implementation does nothing. For robust prefetching, use ReadAt() or ReadAsync().

Public Static Functions

Result<std::shared_ptr<ReadableFile>> Open(const std::string &path, MemoryPool *pool = default_memory_pool())¶

Open a local file for reading.

Return

ReadableFile instance

Parameters

[in] path: with UTF8 encoding
[in] pool: a MemoryPool for memory allocations

Result<std::shared_ptr<ReadableFile>> Open(int fd, MemoryPool *pool = default_memory_pool())¶

Open a local file for reading.

The file descriptor becomes owned by the

ReadableFile, and will be closed on Close() or destruction.

Return

ReadableFile instance

Parameters

[in] fd: file descriptor
[in] pool: a MemoryPool for memory allocations

class arrow::io::FileOutputStream : public arrow::io::OutputStream ¶

An operating system file open in write-only mode.

Public Functions

Status Close() override¶

Close the stream cleanly.

For writable streams, this will attempt to flush any pending data before releasing the underlying resource.

After Close() is called, closed() returns true and the stream is not available for further operations.

bool closed() const override¶: Return whether the stream is closed.

Result<int64_t> Tell() const override¶: Return the position in this stream.

Status Write(const void *data, int64_t nbytes) override¶

Write the given data to the stream.

This method always processes the bytes in full. Depending on the semantics of the stream, the data may be written out immediately, held in a buffer, or written asynchronously. In the case where the stream buffers the data, it will be copied. To avoid potentially large copies, use the Write variant that takes an owned Buffer.

Public Static Functions

Result<std::shared_ptr<FileOutputStream>> Open(const std::string &path, bool append = false)¶

Open a local file for writing, truncating any existing file.

When opening a new file, any existing file with the indicated path is truncated to 0 bytes, deleting any existing data

Return

an open FileOutputStream

Parameters

[in] path: with UTF8 encoding
[in] append: append to existing file, otherwise truncate to 0 bytes

Result<std::shared_ptr<FileOutputStream>> Open(int fd)¶

Open a file descriptor for writing.

The underlying file isn’t truncated.

The file descriptor becomes owned by the

OutputStream, and will be closed on Close() or destruction.

Return

an open FileOutputStream

Parameters

[in] fd: file descriptor

class arrow::io::MemoryMappedFile : public arrow::io::ReadWriteFileInterface ¶

A file interface that uses memory-mapped files for memory interactions.

This implementation supports zero-copy reads. The same class is used for both reading and writing.

If opening a file in a writable mode, it is not truncated first as with FileOutputStream.

Public Functions

Status Close() override¶

Close the stream cleanly.

For writable streams, this will attempt to flush any pending data before releasing the underlying resource.

After Close() is called, closed() returns true and the stream is not available for further operations.

bool closed() const override¶: Return whether the stream is closed.

Result<int64_t> Tell() const override¶: Return the position in this stream.

Result<int64_t> Read(int64_t nbytes, void *out) override¶

Read data from current file position.

Read at most nbytes from the current file position into out. The number of bytes read is returned.

Result<std::shared_ptr<Buffer>> Read(int64_t nbytes) override¶

Read data from current file position.

Read at most nbytes from the current file position. Less bytes may be read if EOF is reached. This method updates the current file position.

In some cases (e.g. a memory-mapped file), this method may avoid a memory copy.

Result<std::shared_ptr<Buffer>> ReadAt(int64_t position, int64_t nbytes) override¶

Read data from given file position.

At most nbytes bytes are read, but it can be less if EOF is reached.

Return

A buffer containing the bytes read, or an error

Parameters

[in] position: Where to read bytes from
[in] nbytes: The number of bytes to read

Result<int64_t> ReadAt(int64_t position, int64_t nbytes, void *out) override¶

Read data from given file position.

At most nbytes bytes are read. The number of bytes read is returned (it can be less than nbytes if EOF is reached).

This method can be safely called from multiple threads concurrently. It is unspecified whether this method updates the file position or not.

The default RandomAccessFile-provided implementation uses Seek() and Read(), but subclasses may override it with a more efficient implementation that doesn’t depend on implicit file positioning.

Return

The number of bytes read, or an error

Parameters

[in] position: Where to read bytes from
[in] nbytes: The number of bytes to read
[out] out: The buffer to read bytes into

Future<std::shared_ptr<Buffer>> ReadAsync(const AsyncContext&, int64_t position, int64_t nbytes) override¶: EXPERIMENTAL: Read data asynchronously.

Status WillNeed(const std::vector<ReadRange> &ranges) override¶

EXPERIMENTAL: Inform that the given ranges may be read soon.

Some implementations might arrange to prefetch some of the data. However, no guarantee is made and the default implementation does nothing. For robust prefetching, use ReadAt() or ReadAsync().

bool supports_zero_copy() const override¶

Return true if InputStream is capable of zero copy Buffer reads.

Zero copy reads imply the use of Buffer-returning Read() overloads.

Status Write(const void *data, int64_t nbytes) override¶: Write data at the current position in the file. Thread-safe.

Status Resize(int64_t new_size)¶: Set the size of the map to new_size.

Status WriteAt(int64_t position, const void *data, int64_t nbytes) override¶: Write data at a particular position in the file. Thread-safe.

Result<int64_t> GetSize() override¶

Return the total file size in bytes.

This method does not read or move the current file position, so is safe to call concurrently with e.g. ReadAt().

Public Static Functions

Result<std::shared_ptr<MemoryMappedFile>> Create(const std::string &path, int64_t size)¶: Create new file with indicated size, return in read/write mode.

Buffering input / output wrappers¶

class arrow::io::BufferedInputStream : public arrow::io::internal::InputStreamConcurrencyWrapper<BufferedInputStream>¶

An InputStream that performs buffered reads from an unbuffered InputStream, which can mitigate the overhead of many small reads in some cases.

Public Functions

Status SetBufferSize(int64_t new_buffer_size)¶

Resize internal read buffer; calls to Read(…) will read at least.

Return

Status

Parameters

[in] new_buffer_size: the new read buffer size

int64_t bytes_buffered() const¶: Return the number of remaining bytes in the read buffer.

int64_t buffer_size() const¶: Return the current size of the internal buffer.

std::shared_ptr<InputStream> Detach()¶

Release the raw InputStream.

Any data buffered will be discarded. Further operations on this object are invalid

Return: raw the underlying InputStream

std::shared_ptr<InputStream> raw() const¶: Return the unbuffered InputStream.

bool closed() const override¶: Return whether the stream is closed.

Public Static Functions

Result<std::shared_ptr<BufferedInputStream>> Create(int64_t buffer_size, MemoryPool *pool, std::shared_ptr<InputStream> raw, int64_t raw_read_bound = -1)¶

Create a BufferedInputStream from a raw InputStream.

Return

the created BufferedInputStream

Parameters

[in] buffer_size: the size of the temporary read buffer
[in] pool: a MemoryPool to use for allocations
[in] raw: a raw InputStream
[in] raw_read_bound: a bound on the maximum number of bytes to read from the raw input stream. The default -1 indicates that it is unbounded

class arrow::io::BufferedOutputStream : public arrow::io::OutputStream ¶

Public Functions

Status SetBufferSize(int64_t new_buffer_size)¶

Resize internal buffer.

Return

Status

Parameters

[in] new_buffer_size: the new buffer size

int64_t buffer_size() const¶: Return the current size of the internal buffer.

int64_t bytes_buffered() const¶: Return the number of remaining bytes that have not been flushed to the raw OutputStream.

Result<std::shared_ptr<OutputStream>> Detach()¶

Flush any buffered writes and release the raw OutputStream.

Further operations on this object are invalid

Return: the underlying OutputStream

Status Close() override¶

Close the buffered output stream.

This implicitly closes the underlying raw output stream.

Status Abort() override¶

Close the stream abruptly.

This method does not guarantee that any pending data is flushed. It merely releases any underlying resource used by the stream for its operation.

After Abort() is called, closed() returns true and the stream is not available for further operations.

bool closed() const override¶: Return whether the stream is closed.

Result<int64_t> Tell() const override¶: Return the position in this stream.

Status Write(const void *data, int64_t nbytes) override¶

Write the given data to the stream.

This method always processes the bytes in full. Depending on the semantics of the stream, the data may be written out immediately, held in a buffer, or written asynchronously. In the case where the stream buffers the data, it will be copied. To avoid potentially large copies, use the Write variant that takes an owned Buffer.

Status Write(const std::shared_ptr<Buffer> &data) override¶

Write the given data to the stream.

Since the Buffer owns its memory, this method can avoid a copy if buffering is required. See Write(const void*, int64_t) for details.

Status Flush() override¶: Flush buffered bytes, if any.

std::shared_ptr<OutputStream> raw() const¶: Return the underlying raw output stream.

Public Static Functions

Result<std::shared_ptr<BufferedOutputStream>> Create(int64_t buffer_size, MemoryPool *pool, std::shared_ptr<OutputStream> raw)¶

Create a buffered output stream wrapping the given output stream.

Return

the created BufferedOutputStream

Parameters

[in] buffer_size: the size of the temporary write buffer
[in] pool: a MemoryPool to use for allocations
[in] raw: another OutputStream

Compressed input / output wrappers¶

class arrow::io::CompressedInputStream : public arrow::io::internal::InputStreamConcurrencyWrapper<CompressedInputStream>¶

Public Functions

bool closed() const override¶: Return whether the stream is closed.

std::shared_ptr<InputStream> raw() const¶: Return the underlying raw input stream.

Public Static Functions

Result<std::shared_ptr<CompressedInputStream>> Make(util::Codec *codec, const std::shared_ptr<InputStream> &raw, MemoryPool *pool = default_memory_pool())¶: Create a compressed input stream wrapping the given input stream.

class arrow::io::CompressedOutputStream : public arrow::io::OutputStream ¶

Public Functions

Status Close() override¶

Close the compressed output stream.

This implicitly closes the underlying raw output stream.

Status Abort() override¶

Close the stream abruptly.

This method does not guarantee that any pending data is flushed. It merely releases any underlying resource used by the stream for its operation.

After Abort() is called, closed() returns true and the stream is not available for further operations.

bool closed() const override¶: Return whether the stream is closed.

Result<int64_t> Tell() const override¶: Return the position in this stream.

Status Write(const void *data, int64_t nbytes) override¶

Write the given data to the stream.

This method always processes the bytes in full. Depending on the semantics of the stream, the data may be written out immediately, held in a buffer, or written asynchronously. In the case where the stream buffers the data, it will be copied. To avoid potentially large copies, use the Write variant that takes an owned Buffer.

Status Flush() override¶: Flush buffered bytes, if any.

std::shared_ptr<OutputStream> raw() const¶: Return the underlying raw output stream.

Public Static Functions

Result<std::shared_ptr<CompressedOutputStream>> Make(util::Codec *codec, const std::shared_ptr<OutputStream> &raw, MemoryPool *pool = default_memory_pool())¶: Create a compressed output stream wrapping the given output stream.