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Fix generating monotonic ULIDs in the same ms #46

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Fix generating monotonic ULIDs in the same ms #46

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8 changes: 8 additions & 0 deletions tests/test_ulid.py
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Original file line number Diff line number Diff line change
Expand Up @@ -74,6 +74,14 @@ def test_same_millisecond_overflow() -> None:
ULID()


def test_same_millisecond_monotonic_sorting_without_frozen_time() -> None:
previous_ulid = ""
for i in range(10000):
new_ulid = ULID()
assert new_ulid > previous_ulid
previous_ulid = new_ulid


def assert_sorted(seq: list) -> None:
last = seq[0]
for item in seq[1:]:
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12 changes: 6 additions & 6 deletions ulid/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -69,18 +69,17 @@ def timestamp(self, value: float | None = None) -> int:
raise ValueError("Value exceeds maximum possible timestamp")
return value

def randomness(self) -> bytes:
def randomness(self, timestamp: int) -> bytes:
with self.lock:
current_timestamp = self.timestamp()
if current_timestamp == self.prev_timestamp:
if timestamp == self.prev_timestamp:
if self.prev_randomness == constants.MAX_RANDOMNESS:
raise ValueError("Randomness within same millisecond exhausted")
randomness = self.increment_bytes(self.prev_randomness)
else:
randomness = os.urandom(constants.RANDOMNESS_LEN)

self.prev_randomness = randomness
self.prev_timestamp = current_timestamp
self.prev_timestamp = timestamp
return randomness

def increment_bytes(self, value: bytes) -> bytes:
Expand Down Expand Up @@ -148,8 +147,9 @@ def from_timestamp(cls, value: float) -> Self:
>>> ULID.from_timestamp(time.time())
ULID(01E75QWN5HKQ0JAVX9FG1K4YP4)
"""
timestamp = int.to_bytes(cls.provider.timestamp(value), constants.TIMESTAMP_LEN, "big")
randomness = cls.provider.randomness()
timestamp_value = cls.provider.timestamp(value)
timestamp = int.to_bytes(timestamp_value, constants.TIMESTAMP_LEN, "big")
randomness = cls.provider.randomness(timestamp_value)
return cls.from_bytes(timestamp + randomness)

@classmethod
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