mps br/vmem: simple-chunk-return:

zcoll.c:
 How to get rid of all the objects, so full collect really collects all automatic objects:
   - Rootdrop() helps, but we can still retain a 1.2MB object;
   - stackwipe() does not help much -- these unwanted ambig refs are being left on the stack by MPS code that runs between mps_arena_collect and the flip!
   - therefore StackScan(0/1) to destroy stack+reg root before full collect: it's the only way to be sure.

 Reproducibility:
   - give Make() a random? switch, acted on by df() = diversity function, to allow bypass of rnd();
   - ZRndStateSet, to set the seed for rnd()

 Output:
   - print_M: switchable Mebibytes or Megabytes (more useful, to be honest);
   - get(): don't report message times, it messes up diffs.

 testlib.c/h:
 Reproducibility:
   - fix rnd_state so a rnd_state getter is possible;
   - testlib.h += rnd_state_t, rnd_state(), rnd_state_set(), rnd_state_set_v2()

 trace.c: traceFindGrey diag: no newline please

Copied from Perforce
 Change: 170093
 ServerID: perforce.ravenbrook.com

1 files changed, 70 insertions, 18 deletions

diff --git a/mps/code/testlib.c b/mps/code/testlib.c
index 71cc05d330e..0bc8771f134 100644
--- a/mps/code/testlib.c
+++ b/mps/code/testlib.c
@@ -221,48 +221,100 @@ mps_addr_t rnd_addr(void)
 }
 
 
-/* randomize -- randomize the generator, or initialize to replay */
+/* randomize -- randomize the generator, or initialize to replay
+ *
+ * There have been 3 versions of the rnd-states reported by this 
+ * function:
+ *
+ * 1. before RHSK got his hands on rnd().  These seed values are not 
+ *    currently supported, but it might be easy to add support.
+ *
+ * 2. v2 states: the published "seed" (state) value was the seed 
+ *    *before* the 10 rnds to churn up and separate nearby values 
+ *    from time().  This is unfortunate: you can't write a rnd_state 
+ *    getter, because it would have to go 10 steps back in time.
+ *
+ * 3. v3 states: when autogenerated from time(), the published 
+ *    state is that *after* the 10 rnds.  Therefore you can get this 
+ *    easily, store it, re-use it, etc.
+ */
 
 void randomize(int argc, char **argv)
 {
+  int i;
   int n;
+  unsigned long seedt;
   unsigned long seed0;
-  int i;
 
   if (argc > 1) {
     n = sscanf(argv[1], "%lu", &seed0);
     Insist(n == 1);
-    printf("randomize(): resetting initial seed to: %lu.\n", seed0);
+    printf("randomize(): resetting initial state (v3) to: %lu.\n", seed0);
+    rnd_state_set(seed0);
   } else {
     /* time_t uses an arbitrary encoding, but hopefully the low order */
     /* 31 bits will have at least one bit changed from run to run. */
-    seed0 = 1 + time(NULL) % (R_m - 1);
-    printf("randomize(): choosing initial seed: %lu.\n", seed0);
+    seedt = 1 + time(NULL) % (R_m - 1);
+
+    /* The value returned by time() on some OSs may simply be a 
+     * count of seconds: therefore successive runs may start with 
+     * nearby seeds, possibly differing only by 1.  So the first value
+     * returned by rnd() may differ by only 48271.  It is conceivable 
+     * that some tests might be able to 'spot' this pattern (for 
+     * example: by using the first rnd() value, mod 100M and rounded 
+     * to multiple of 1024K, as arena size in bytes).
+     * 
+     * So to mix it up a bit, we do a few iterations now.  How many?  
+     * Very roughly, 48271^2 is of the same order as 2^31, so two 
+     * iterations would make the characteristic difference similar to 
+     * the period.  Hey, let's go wild and do 10.
+     */
+    rnd_state_set(seedt);
+    for(i = 0; i < 10; i += 1) {
+      (void)rnd();
+    }
+
+    seed0 = rnd_state();
+    printf("randomize(): choosing initial state (v3): %lu.\n", seed0);
+    rnd_state_set(seed0);
   }
+}
+
+unsigned long rnd_state(void)
+{
+  return seed;
+}
 
+void rnd_state_set(unsigned long seed0)
+{
   Insist(seed0 < R_m);
   Insist(seed0 != 0);
   seed = seed0;
 
   rnd_verify(0);
   Insist(seed == seed0);
+}
+
+/* rnd_state_set_2 -- legacy support for v2 rnd states
+ *
+ * In v2, the published "seed" (state) value was the seed *before* 
+ * the 10 rnds to churn up and separate nearby values from time().
+ *
+ * Set the seed, then convert it to a v3 state by doing those 10 rnds.
+ */
+void rnd_state_set_v2(unsigned long seed0_v2)
+{
+  int i;
+  unsigned long seed0;
 
-  /* The 'random' seed is taken from time(), which may simply be a 
-   * count of seconds: therefore successive runs may start with 
-   * nearby seeds, possibly differing only by 1.  So the first value
-   * returned by rnd() may differ by only 48271.  It is conceivable 
-   * that some tests might be able to 'spot' this pattern (for 
-   * example: by using the first rnd() value, mod 100M and rounded 
-   * to multiple of 1024K, as arena size in bytes).
-   * 
-   * So to mix it up a bit, we do a few iterations now.  How many?  
-   * Very roughly, 48271^2 is of the same order as 2^31, so two 
-   * iterations would make the characteristic difference similar to 
-   * the period.  Hey, let's go wild and do 10.
-   */
+  rnd_state_set(seed0_v2);
   for(i = 0; i < 10; i += 1) {
     (void)rnd();
   }
+
+  seed0 = rnd_state();
+  printf("rnd_state_set_v2(): seed0_v2 = %lu, converted to state_v3 = %lu.\n", seed0_v2, seed0);
+  rnd_state_set(seed0);
 }