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* Buffer reads in FdSource. Together with write buffering, this

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significantly cuts down the number of syscalls (e.g., for "nix-store
  -qR /var/run/current-system" via the daemon, it reduced the number
  of syscalls in the client from 29134 to 4766 and in the daemon from
  44266 to 20666).
This commit is contained in:
Eelco Dolstra 2011-12-15 12:32:08 +00:00
parent 3a48282b06
commit a3e0656cbb
2 changed files with 32 additions and 10 deletions
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24
src/libutil/serialise.cc
View file

@ -2,6 +2,7 @@
#include "util.hh"
#include <cstring>
#include <cerrno>
namespace nix {
@ -38,7 +39,28 @@ void FdSink::flush()
void FdSource::operator () (unsigned char * data, unsigned int len)
{
readFull(fd, data, len);
if (!buffer) buffer = new unsigned char[bufSize];
while (len) {
if (!bufPosIn) {
/* Read as much data as is available (up to the buffer
size). */
checkInterrupt();
ssize_t n = read(fd, (char *) buffer, bufSize);
if (n == -1) {
if (errno == EINTR) continue;
throw SysError("reading from file");
}
if (n == 0) throw EndOfFile("unexpected end-of-file");
bufPosIn = n;
}
/* Copy out the data in the buffer. */
size_t n = len > bufPosIn - bufPosOut ? bufPosIn - bufPosOut : len;
memcpy(data, buffer + bufPosOut, n);
data += n; bufPosOut += n; len -= n;
if (bufPosIn == bufPosOut) bufPosIn = bufPosOut = 0;
}
}

18
src/libutil/serialise.hh
View file

@ -38,9 +38,7 @@ struct FdSink : Sink
FdSink() : fd(-1), bufSize(32 * 1024), bufPos(0), buffer(0) { }
FdSink(int fd, unsigned int bufSize = 32 * 1024)
: fd(fd), bufSize(bufSize), bufPos(0), buffer(0)
{
}
: fd(fd), bufSize(bufSize), bufPos(0), buffer(0) { }
~FdSink()
{
@ -58,15 +56,17 @@ struct FdSink : Sink
struct FdSource : Source
{
int fd;
unsigned int bufSize, bufPosIn, bufPosOut;
unsigned char * buffer;
FdSource()
{
fd = -1;
}
FdSource() : fd(-1), bufSize(32 * 1024), bufPosIn(0), bufPosOut(0), buffer(0) { }
FdSource(int fd)
FdSource(int fd, unsigned int bufSize = 32 * 1024)
: fd(fd), bufSize(bufSize), bufPosIn(0), bufPosOut(0), buffer(0) { }
~FdSource()
{
this->fd = fd;
if (buffer) delete[] buffer;
}
void operator () (unsigned char * data, unsigned int len);