Call reseed in fork process (#108)

* Call reseed in fork process

* update

Author: aminalaee

README.md

@@ -70,24 +70,6 @@ in comparison with the `uuid_utils` default behaviour, but is still faster than
 UUID('ffe95fcc-b818-4aca-a350-e0a35b9de6ec')
 ```
 
-## Fork processes
-
-The underlying Rust library for generating random values is not guaranteed to reseed when you fork the process. This would mean that after forking, the `uuid_utils` calls can return the same value for a few calls, and then it reseeds.
-
-If you plan to use this library alongside forking you will want to explicitly reseed post-fork. You can do this with:
-
-```py
-import os
-
-import uuid_utils
-
-# Calling it manually when forking
-uuid_utils.reseed_rng()
-
-# Or registering it to be called when forking
-os.register_at_fork(uuid_utils.reseed_rng)
-```
-
 ## Benchmarks
 
 | Benchmark        | Min   | Max   | Mean  | Min (+)       | Max (+)       | Mean (+)      |

docs/index.md

@@ -76,24 +76,6 @@ in comparison with the `uuid_utils` default behaviour, but is still faster than
 UUID('ffe95fcc-b818-4aca-a350-e0a35b9de6ec')
 ```
 
-## Fork processes
-
-The underlying Rust library for generating random values is not guaranteed to reseed when you fork the process. This would mean that after forking, the `uuid_utils` calls can return the same value for a few calls, and then it reseeds.
-
-If you plan to use this library alongside forking you will want to explicitly reseed post-fork. You can do this with:
-
-```py
-import os
-
-import uuid_utils
-
-# Calling it manually when forking
-uuid_utils.reseed_rng()
-
-# Or registering it to be called when forking
-os.register_at_fork(uuid_utils.reseed_rng)
-```
-
 ## Benchmarks
 
 | Benchmark        | Min   | Max   | Mean  | Min (+)       | Max (+)       | Mean (+)      |

python/uuid_utils/__init__.py

@@ -1,3 +1,4 @@
+import os
 from uuid import SafeUUID
 
 from ._uuid_utils import (
@@ -14,7 +15,6 @@
     UUID,
     __version__,
     getnode,
-    reseed_rng,
     uuid1,
     uuid3,
     uuid4,
@@ -23,6 +23,14 @@
     uuid7,
     uuid8,
 )
+from ._uuid_utils import (
+    reseed as reseed_rng,
+)
+
+# Reseed the RNG in the child process after a fork.
+# Otherwise both parent and child processes may generate the same UUIDs for some time.
+if hasattr(os, "fork"):
+    os.register_at_fork(after_in_child=reseed_rng)
 
 __all__ = [
     "MAX",

src/lib.rs

@@ -427,7 +427,7 @@ fn getnode() -> PyResult<u64> {
 }
 
 #[pyfunction]
-fn reseed_rng() -> PyResult<()> {
+fn reseed() -> PyResult<()> {
     rand::rng()
         .reseed()
         .map_err(|err| PyOSError::new_err(err.to_string()))
@@ -457,7 +457,7 @@ fn _uuid_utils(m: &Bound<'_, PyModule>) -> PyResult<()> {
     m.add_function(wrap_pyfunction!(uuid7, m)?)?;
     m.add_function(wrap_pyfunction!(uuid8, m)?)?;
     m.add_function(wrap_pyfunction!(getnode, m)?)?;
-    m.add_function(wrap_pyfunction!(reseed_rng, m)?)?;
+    m.add_function(wrap_pyfunction!(reseed, m)?)?;
     m.add("NAMESPACE_DNS", UUID::NAMESPACE_DNS)?;
     m.add("NAMESPACE_URL", UUID::NAMESPACE_URL)?;
     m.add("NAMESPACE_OID", UUID::NAMESPACE_OID)?;

tests/test_uuid.py

@@ -208,16 +208,13 @@ def test_getnode() -> None:
 
 
 @pytest.mark.skipif(sys.platform == "win32", reason="Does not run on Windows")
-def test_reseed_rng_with_fork() -> None:
+def test_reseed_is_called_when_forking() -> None:
     read_end, write_end = os.pipe()
-    # forcibly generate uuid before fork to have rng state
     uuid_utils.uuid4()
 
-    pid = os.fork()  # type: ignore[attr-defined]
+    pid = os.fork()
     if pid == 0:
         os.close(read_end)
-        # explicity reseed in the child
-        uuid_utils.reseed_rng()
         next_uuid_child = str(uuid_utils.uuid4())
         with os.fdopen(write_end, "w") as write_pipe:
             write_pipe.write(next_uuid_child)
@@ -229,7 +226,6 @@ def test_reseed_rng_with_fork() -> None:
     with os.fdopen(read_end) as read_pipe:
         uuid_from_pipe = uuid_utils.UUID(read_pipe.read())
 
-    # the uuids should be different because we reseeded
     assert next_parent_uuid != uuid_from_pipe