GH-120754: Make PY_READ_MAX smaller than max byteobject size #121633
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Currently if code tries to do a os.read larger than the max bytes object length, the size to read gets capped to `_PY_READ_MAX`, then the code tries to allocate a PyBytes which fails with an OverflowError as the size is larger than the max py bytes object. Since os.read is capping the max size anyways, cap it to a size which is always allocatable as a PyBytes. This changes behavior from bpo-21932 and enables the large file os.read test on 32 bit platforms, as it should cap the read to a platform acceptable size.
cmaloney
changed the title
cmaloney
commented
Jul 15, 2024
| Cap read size to smaller than the max BytesObject size. read() in POSIX | ||
| returns at most the number of requseted bytes, this updates python ``os.read`` | ||
| to do similarly, and rather than throw an OverflowError in this case, return | ||
| a smaller than requseted byte object. |
cmaloney
commented
Jul 17, 2024
| # Skip the test on 32-bit platforms: the number of bytes must fit in a | ||
| # Py_ssize_t type | ||
| @unittest.skipUnless(INT_MAX < PY_SSIZE_T_MAX, | ||
| "needs INT_MAX < PY_SSIZE_T_MAX") | ||
| @support.bigmemtest(size=INT_MAX + 10, memuse=1, dry_run=False) |
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issue here is that this will result in a memory allocation error on 32 bit machines, and this bigmemtest effectively makes it not run on 32 bit machines (They are unlikely to have that much RAM)
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Currently if code tries to do a os.read larger than the max bytes object length, the size to read gets capped to
_PY_READ_MAX, then the code tries to allocate a PyBytes which fails with an OverflowError as the size is longer than what is allocatable.Since os.read is capping the max size anyways, cap it to a size which is always allocatable as a PyBytes.
This changes behavior from bpo-21932 and enables the large file os.read test on 32 bit platforms, as it should cap the read to a platform acceptable size.