introduce a config flag to control a random seed offset

jax/_src/config.py

@@ -210,6 +210,7 @@ def _trace_context(self):
             self.jax_numpy_rank_promotion, self.jax_default_matmul_precision,
             self.jax_dynamic_shapes, self.jax_numpy_dtype_promotion,
             self.jax_default_device,
+            self.jax_random_seed_offset,
             self.jax_threefry_partitionable,
             self.jax_softmax_custom_jvp,
             self.jax_enable_memories,
@@ -655,6 +656,7 @@ class _GlobalExtraJitContext(NamedTuple):
   numpy_dtype_promotion: str | None = None
   default_matmul_precision: Any | None = None
   dynamic_shapes: bool = False
+  random_seed_offset: int = 0
   threefry_partitionable: bool = False
   softmax_custom_jvp: bool = False
   xla_profile_version: int = 0
@@ -682,6 +684,7 @@ class _ThreadLocalExtraJitContext(NamedTuple):
   numpy_dtype_promotion: str | None = None
   default_matmul_precision: Any | None = None
   dynamic_shapes: bool = False
+  random_seed_offset: int = 0
   threefry_partitionable: bool = False
   softmax_custom_jvp: bool = False
   xla_profile_version: int = 0
@@ -868,6 +871,16 @@ def _update_jax_memories_thread_local(val):
           'computations. Logging is performed with `logging` at WARNING '
           'level.'))
 
+random_seed_offset = define_int_state(
+    name='jax_random_seed_offset',
+    default=0,
+    help=('Offset to all random seeds (e.g. argument to jax.random.key()).'),
+    update_global_hook=lambda val: _update_global_jit_state(
+        random_seed_offset=val),
+    update_thread_local_hook=lambda val: update_thread_local_jit_state(
+        random_seed_offset=val)
+)
+
 legacy_prng_key = define_enum_state(
     name='jax_legacy_prng_key',
     enum_values=['allow', 'warn', 'error'],

jax/_src/prng.py

@@ -733,6 +733,8 @@ def random_seed(seeds: int | typing.ArrayLike, impl: PRNGImpl) -> PRNGKeyArrayIm
     seeds_arr = jnp.asarray(np.int64(seeds))
   else:
     seeds_arr = jnp.asarray(seeds)
+  if config.random_seed_offset.value:
+    seeds_arr += config.random_seed_offset.value
   return random_seed_p.bind(seeds_arr, impl=impl)
 
 random_seed_p = core.Primitive('random_seed')

tests/random_test.py

@@ -399,6 +399,14 @@ def testPRNGValues(self, make_key):
         random.key_data(random.fold_in(k, 4)),
         np.array([2285895361,  433833334], dtype='uint32'))
 
+  @parameterized.parameters([{'make_key': ctor} for ctor in KEY_CTORS])
+  def test_random_seed_offset(self, make_key):
+    k1 = make_key(17)
+    with config.random_seed_offset(3):
+      k2 = make_key(17)
+    eq = k1 == k2 if k2.ndim == 0 else all(k1 == k2)
+    self.assertFalse(eq)
+
   @parameterized.parameters([{'make_key': ctor} for ctor in KEY_CTORS])
   def test_random_bits_error(self, make_key):
     msg = 'dtype argument .* must be an unsigned int dtype'