git » libfiu » commit 780aa56

diff --git a/bindings/python/fiu.py b/bindings/python/fiu.py
index 0b0a308..20f4a13 100644
--- a/bindings/python/fiu.py
+++ b/bindings/python/fiu.py
@@ -95,6 +95,11 @@ def disable(name):
 	if r != 0:
 		raise RuntimeError(r)
 
+def set_prng_seed(seed):
+	"""Sets the PRNG seed. Don't use this unless you know what you're
+	doing."""
+	return _ll.set_prng_seed(seed)
+
 def rc_fifo(basename):
 	"""Enables remote control over a named pipe that begins with the given
 	basename. The final path will be "basename-$PID"."""
diff --git a/bindings/python/fiu_ll.c b/bindings/python/fiu_ll.c
index e49874b..85ca93b 100644
--- a/bindings/python/fiu_ll.c
+++ b/bindings/python/fiu_ll.c
@@ -187,6 +187,17 @@ static PyObject *disable(PyObject *self, PyObject *args)
 	return PyLong_FromLong(fiu_disable(name));
 }
 
+static PyObject *set_prng_seed(PyObject *self, PyObject *args)
+{
+	int seed;
+
+	if (!PyArg_ParseTuple(args, "i:set_prng_seed", &seed))
+		return NULL;
+
+	fiu_set_prng_seed(seed);
+	Py_RETURN_NONE;
+}
+
 static PyObject *rc_fifo(PyObject *self, PyObject *args)
 {
 	char *basename;
@@ -207,6 +218,7 @@ static PyMethodDef fiu_methods[] = {
 	{ "enable_stack_by_name", (PyCFunction) enable_stack_by_name,
 		METH_VARARGS, NULL },
 	{ "disable", (PyCFunction) disable, METH_VARARGS, NULL },
+	{ "set_prng_seed", (PyCFunction) set_prng_seed, METH_VARARGS, NULL },
 	{ "rc_fifo", (PyCFunction) rc_fifo, METH_VARARGS, NULL },
 	{ NULL }
 };
diff --git a/libfiu/fiu.c b/libfiu/fiu.c
index 4f9de64..e49bfc2 100644
--- a/libfiu/fiu.c
+++ b/libfiu/fiu.c
@@ -191,11 +191,17 @@ static int should_stack_fail(struct pf_info *pf)
  * To seed it, we use the current microseconds. To prevent seed reuse, we
  * re-seed after each fork (see atfork_child()). */
 static unsigned int randd_xn = 0xA673F42D;
+static bool randd_xn_manual = false;
 
 static void prng_seed(void)
 {
 	struct timeval tv;
 
+	/* If the seed is being handled manually, don't interfere. */
+	if (randd_xn_manual) {
+		return;
+	}
+
 	gettimeofday(&tv, NULL);
 
 	randd_xn = tv.tv_usec;
@@ -255,6 +261,13 @@ int fiu_init(unsigned int flags)
 	return 0;
 }
 
+/* Sets the PRNG seed. */
+void fiu_set_prng_seed(unsigned int seed)
+{
+	randd_xn = seed;
+	randd_xn_manual = true;
+}
+
 /* Returns the failure status of the given name. Must work well even before
  * fiu_init() is called assuming no points of failure are enabled; although it
  * can (and does) assume fiu_init() will be called before enabling any. */
diff --git a/libfiu/fiu.h b/libfiu/fiu.h
index 7659b7f..8dd6bb7 100644
--- a/libfiu/fiu.h
+++ b/libfiu/fiu.h
@@ -30,6 +30,21 @@ extern "C" {
  */
 int fiu_init(unsigned int flags);
 
+/** Sets the PRNG seed.
+ *
+ * This function is called if you want to manually set the seed used to
+ * generate random numbers.  This allows more control over randomized tests.
+ *
+ * Must be called before fiu_init(), or at fork. Otherwise, races might occur
+ * as this function is not threadsafe wrt. other fiu functions.
+ *
+ * There's no need to call this function for normal operations. Don't use it
+ * unless you know what you're doing.
+ *
+ * @param seed  PRNG seed to use.
+ */
+void fiu_set_prng_seed(unsigned int seed);
+
 /** Returns the failure status of the given point of failure.
  *
  * @param name  Point of failure name.
@@ -73,6 +88,7 @@ void *fiu_failinfo(void);
  * don't include it to avoid a circular dependency. */
 
 #define fiu_init(flags) 0
+#define fiu_set_prng_seed(seed)
 #define fiu_fail(name) 0
 #define fiu_failinfo() NULL
 #define fiu_do_on(name, action)
diff --git a/libfiu/symbols.map b/libfiu/symbols.map
index 204acc1..bae73d5 100644
--- a/libfiu/symbols.map
+++ b/libfiu/symbols.map
@@ -10,6 +10,7 @@
 		fiu_fail;
 		fiu_failinfo;
 		fiu_init;
+		fiu_set_prng_seed;
 		fiu_rc_fifo;
 		fiu_rc_string;
 
diff --git a/tests/test-set_prng_seed.py b/tests/test-set_prng_seed.py
new file mode 100644
index 0000000..f1f3f5c
--- /dev/null
+++ b/tests/test-set_prng_seed.py
@@ -0,0 +1,23 @@
+"""
+Test that we get reproducible results with manually set PRNG seeds.
+"""
+
+import fiu
+
+
+fiu.set_prng_seed(1234)
+fiu.enable_random('p1', probability = 0.5)
+result = { True: 0, False: 0 }
+for i in range(1000):
+    result[fiu.fail('p1')] += 1
+
+assert result == {False: 516, True: 484}, result
+
+
+fiu.set_prng_seed(4321)
+fiu.enable_random('p1', probability = 0.5)
+result = { True: 0, False: 0 }
+for i in range(1000):
+    result[fiu.fail('p1')] += 1
+
+assert result == {False: 495, True: 505}, result