circuitpython/tests/extmod/btree_gc.py
Damien George 73c58150f5 extmod/modbtree: Retain reference to underlying stream so it's not GC'd.
For ports that have a system malloc which is not garbage collected (eg
unix, esp32), the stream object for the DB must be retained separately to
prevent it from being reclaimed by the MicroPython GC (because the
berkeley-db library uses malloc to allocate the DB structure which stores
the only reference to the stream).

Although in some cases the user code will explicitly retain a reference to
the underlying stream because it needs to call close() on it, this is not
always the case, eg in cases where the DB is intended to live forever.

Fixes issue #5940.
2020-05-02 16:08:04 +10:00

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Python

# Test btree interaction with the garbage collector.
try:
import btree, uio, gc
except ImportError:
print("SKIP")
raise SystemExit
N = 80
# Create a BytesIO but don't keep a reference to it.
db = btree.open(uio.BytesIO(), pagesize=512)
# Overwrite lots of the Python stack to make sure no reference to the BytesIO remains.
x = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
# Write lots of key/value pairs, which fill up the DB and also allocate temporary heap
# memory due to the string addition, and do a GC collect to verify that the BytesIO
# is not collected.
for i in range(N):
db[b"thekey" + str(i)] = b"thelongvalue" + str(i)
print(db[b"thekey" + str(i)])
gc.collect()