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Speed up read() (i.e. read till EOF) considerably by doing a stat() to 

see if we can guess the #bytes until the end of the file.  If we
can't, increment the buffer size increments up to 0.5Meg to avoid
realloc'ing too much.
This commit is contained in:
Guido van Rossum 1997-05-09 22:27:31 +00:00
parent 5878b662de
commit 5449b6e123
1 changed files with 65 additions and 15 deletions
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80
Objects/fileobject.c
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@ -381,47 +381,97 @@ file_isatty(f, args)
return PyInt_FromLong(res);
}
/* We expect that fstat exists on most systems.
It's confirmed on Unix, Mac and Windows.
If you don't have it, add #define DONT_HAVE_FSTAT to your config.h. */
#ifndef DONT_HAVE_FSTAT
#define HAVE_FSTAT
#include <sys/types.h>
#include <sys/stat.h>
#endif
#if BUFSIZ < 8192
#define SMALLCHUNK 8192
#else
#define SMALLCHUNK BUFSIZ
#endif
#define BIGCHUNK (512*1024)
static size_t
new_buffersize(f, currentsize)
PyFileObject *f;
size_t currentsize;
{
#ifdef HAVE_FSTAT
long pos, end;
struct stat st;
if (fstat(fileno(f->f_fp), &st) == 0) {
end = st.st_size;
pos = ftell(f->f_fp);
if (end > pos && pos >= 0)
return end - pos + 1;
}
#endif
if (currentsize > SMALLCHUNK) {
/* Keep doubling until we reach BIGCHUNK;
then keep adding BIGCHUNK. */
if (currentsize <= BIGCHUNK)
return currentsize + currentsize;
else
return currentsize + BIGCHUNK;
}
return currentsize + SMALLCHUNK;
}
static PyObject *
file_read(f, args)
PyFileObject *f;
PyObject *args;
{
int n, n1, n2, n3;
long bytesrequested;
size_t bytesread, buffersize, chunksize;
PyObject *v;
if (f->f_fp == NULL)
return err_closed();
if (args == NULL)
n = -1;
bytesrequested = -1;
else {
if (!PyArg_Parse(args, "i", &n))
if (!PyArg_Parse(args, "l", &bytesrequested))
return NULL;
}
n2 = n >= 0 ? n : BUFSIZ;
v = PyString_FromStringAndSize((char *)NULL, n2);
if (bytesrequested < 0)
buffersize = new_buffersize(f, 0);
else
buffersize = bytesrequested;
v = PyString_FromStringAndSize((char *)NULL, buffersize);
if (v == NULL)
return NULL;
n1 = 0;
bytesread = 0;
Py_BEGIN_ALLOW_THREADS
for (;;) {
n3 = fread(BUF(v)+n1, 1, n2-n1, f->f_fp);
chunksize = fread(BUF(v) + bytesread, 1,
buffersize - bytesread, f->f_fp);
/* XXX Error check? */
if (n3 == 0)
if (chunksize == 0)
break;
n1 += n3;
if (n1 == n)
bytesread += chunksize;
if (bytesread < buffersize)
break;
if (n < 0) {
n2 = n1 + BUFSIZ;
if (bytesrequested < 0) {
buffersize = new_buffersize(f, buffersize);
Py_BLOCK_THREADS
if (_PyString_Resize(&v, n2) < 0)
if (_PyString_Resize(&v, buffersize) < 0)
return NULL;
Py_UNBLOCK_THREADS
}
}
Py_END_ALLOW_THREADS
if (n1 != n2)
_PyString_Resize(&v, n1);
if (bytesread != buffersize)
_PyString_Resize(&v, bytesread);
return v;
}