data.ulid - Use internal random source for default

Using default-random-source causes ULID conflict for multiple runs of
the program when the user doesn't randomize it.
Cf. #873

ChangeLog

@@ -1,3 +1,11 @@
+2023-01-22  Shiro Kawai  <shiro@acm.org>
+
+	* lib/data/ulid.scm (make-ulid-generator): Use internal random source
+	  when random-source argument is omitted.  Using default-random-source
+	  causes ULID conflict for multiple runs if the user didn't randomize
+	  it beforehand.
+	  https://github.com/shirok/Gauche/issues/873
+
 2023-01-20  Shiro Kawai  <shiro@acm.org>
 
 	* src/compile-1.scm (pass1/body-rec): Make duplicate internal

doc/modutil.texi

@@ -7439,7 +7439,7 @@ Creates and returns a generator that yields a fresh ULID object
 every time it is called.  The optional @var{random-source} argument
 is a SRFI-27 random source (@pxref{Sources of random bits})
 to be used for the random part of ULID.  When omitted,
-SRFI-27's @code{default-random-source} is used.
+an internal random source is used.
 
 To guarantee uniqueness and monotonicity, a ULID generator needs to
 keep internal state.  If you want to share the generator among multiple threads,

lib/data/ulid.scm

@@ -63,12 +63,16 @@
   (timestamp ulid-timestamp)
   (randomness ulid-randomness))
 
+(define ulid-random-source
+  (rlet1 s (make-random-source)
+    (random-source-randomize! s)))
+
 ;; API
 ;; NB: The ULID spec says ULID generation may fail if randomness is very close
 ;; to 2^80 and lots of ULIDs are generated in the same millisecond, causing
 ;; randomness field to overflow.  We can, however, wait just one millisecond
 ;; to overcome that situation.
-(define (make-ulid-generator :optional (random-source default-random-source))
+(define (make-ulid-generator :optional (random-source ulid-random-source))
   (let ((randomness (random-source-make-integers random-source))
         (last-ts 0)
         (last-rn 0))