ClickHouse/dbms/src/IO/ReadBufferFromFileDescriptor.cpp

#include <errno.h>
#include <time.h>

#include <experimental/optional>

#include <DB/Common/ProfileEvents.h>
#include <DB/Common/Stopwatch.h>

#include <DB/Common/Exception.h>
#include <DB/Common/CurrentMetrics.h>

#include <DB/IO/ReadBufferFromFileDescriptor.h>
#include <DB/IO/WriteHelpers.h>


namespace ProfileEvents
{
	extern const Event ReadBufferFromFileDescriptorRead;
	extern const Event ReadBufferFromFileDescriptorReadBytes;
	extern const Event Seek;
}

namespace CurrentMetrics
{
	extern const Metric Read;
}

namespace DB
{

namespace ErrorCodes
{
	extern const int CANNOT_READ_FROM_FILE_DESCRIPTOR;
	extern const int ARGUMENT_OUT_OF_BOUND;
	extern const int CANNOT_SEEK_THROUGH_FILE;
	extern const int CANNOT_SELECT;
}


std::string ReadBufferFromFileDescriptor::getFileName() const
{
	return "(fd = " + toString(fd) + ")";
}


bool ReadBufferFromFileDescriptor::nextImpl()
{
	size_t bytes_read = 0;
	while (!bytes_read)
	{
		ProfileEvents::increment(ProfileEvents::ReadBufferFromFileDescriptorRead);

		std::experimental::optional<Stopwatch> watch;
		if (profile_callback)
			watch.emplace(clock_type);

		ssize_t res = 0;
		{
			CurrentMetrics::Increment metric_increment{CurrentMetrics::Read};
			res = ::read(fd, internal_buffer.begin(), internal_buffer.size());
		}
		if (!res)
			break;

		if (-1 == res && errno != EINTR)
			throwFromErrno("Cannot read from file " + getFileName(), ErrorCodes::CANNOT_READ_FROM_FILE_DESCRIPTOR);

		if (res > 0)
			bytes_read += res;

		if (profile_callback)
		{
			ProfileInfo info;
			info.bytes_requested = internal_buffer.size();
			info.bytes_read = res;
			info.nanoseconds = watch->elapsed();
			profile_callback(info);
		}
	}

	pos_in_file += bytes_read;

	if (bytes_read)
	{
		ProfileEvents::increment(ProfileEvents::ReadBufferFromFileDescriptorReadBytes, bytes_read);
		working_buffer.resize(bytes_read);
	}
	else
		return false;

	return true;
}


/// If 'offset' is small enough to stay in buffer after seek, then true seek in file does not happen.
off_t ReadBufferFromFileDescriptor::doSeek(off_t offset, int whence)
{
	off_t new_pos = offset;
	if (whence == SEEK_CUR)
		new_pos = pos_in_file - (working_buffer.end() - pos) + offset;
	else if (whence != SEEK_SET)
		throw Exception("ReadBufferFromFileDescriptor::seek expects SEEK_SET or SEEK_CUR as whence", ErrorCodes::ARGUMENT_OUT_OF_BOUND);

	/// Position is unchanged.
	if (new_pos + (working_buffer.end() - pos) == pos_in_file)
		return new_pos;

	if (hasPendingData() && new_pos <= pos_in_file && new_pos >= pos_in_file - static_cast<off_t>(working_buffer.size()))
	{
		/// Position is still inside buffer.
		pos = working_buffer.begin() + (new_pos - (pos_in_file - working_buffer.size()));
		return new_pos;
	}
	else
	{
		ProfileEvents::increment(ProfileEvents::Seek);

		pos = working_buffer.end();
		off_t res = lseek(fd, new_pos, SEEK_SET);
		if (-1 == res)
			throwFromErrno("Cannot seek through file " + getFileName(), ErrorCodes::CANNOT_SEEK_THROUGH_FILE);
		pos_in_file = new_pos;
		return res;
	}
}


/// Assuming file descriptor supports 'select', check that we have data to read or wait until timeout.
bool ReadBufferFromFileDescriptor::poll(size_t timeout_microseconds)
{
	fd_set fds;
	FD_ZERO(&fds);
	FD_SET(fd, &fds);
	timeval timeout = { time_t(timeout_microseconds / 1000000), suseconds_t(timeout_microseconds % 1000000) };

	int res = select(1, &fds, 0, 0, &timeout);

	if (-1 == res)
		throwFromErrno("Cannot select", ErrorCodes::CANNOT_SELECT);

	return res > 0;
}

}