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Issue #13159: Replace FileIO's quadratic-time buffer growth algorithm with a linear-time one.

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Also fix the bz2 module, whose classes used the same algorithm.
This commit is contained in:
Nadeem Vawda 2011-10-13 13:34:16 +02:00
parent f1ab47ebc4
commit d41a98bdd9
3 changed files with 11 additions and 30 deletions
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3
Misc/NEWS
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@ -121,6 +121,9 @@ Tests
Extension Modules
-----------------
- Issue #13159: FileIO and BZ2File now use a linear-time buffer growth
strategy instead of a quadratic-time one.
- Issue #13070: Fix a crash when a TextIOWrapper caught in a reference cycle
would be finalized after the reference to its underlying BufferedRWPair's
writer got cleared by the GC.

19
Modules/_io/fileio.c
View file

@ -43,12 +43,6 @@
#define SMALLCHUNK BUFSIZ
#endif
#if SIZEOF_INT < 4
#define BIGCHUNK (512 * 32)
#else
#define BIGCHUNK (512 * 1024)
#endif
typedef struct {
PyObject_HEAD
int fd;
@ -565,15 +559,10 @@ new_buffersize(fileio *self, size_t currentsize)
}
}
#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;
/* Expand the buffer by an amount proportional to the current size,
giving us amortized linear-time behavior. Use a less-than-double
growth factor to avoid excessive allocation. */
return currentsize + (currentsize >> 3) + 6;
}
static PyObject *

19
Modules/bz2module.c
View file

@ -218,25 +218,14 @@ Util_CatchBZ2Error(int bzerror)
#define SMALLCHUNK BUFSIZ
#endif
#if SIZEOF_INT < 4
#define BIGCHUNK (512 * 32)
#else
#define BIGCHUNK (512 * 1024)
#endif
/* This is a hacked version of Python's fileobject.c:new_buffersize(). */
static size_t
Util_NewBufferSize(size_t currentsize)
{
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;
/* Expand the buffer by an amount proportional to the current size,
giving us amortized linear-time behavior. Use a less-than-double
growth factor to avoid excessive allocation. */
return currentsize + (currentsize >> 3) + 6;
}
/* This is a hacked version of Python's fileobject.c:get_line(). */