Support skips with hash syntax.

core/src/main/grammar/crontab.g

@@ -108,13 +108,13 @@ throws ANTLRException
   {
     bits = doRange(d,field);
   }
-  | ("H" "(")=> "H" "(" s=token "-" e=token ")"
+  | ("H" "(")=> "H" "(" s=token "-" e=token ")" ( "/" d=token )?
   {
-    bits = doHash(s,e);
+    bits = doHash(s,e,d);
   }
-  | "H"
+  | "H" ( "/" d=token )?
   {
-    bits = doHash(field);
+    bits = doHash(d,field);
   }
   ;
 

core/src/main/java/hudson/scheduler/BaseParser.java

@@ -88,16 +88,31 @@ abstract class BaseParser extends LLkParser {
     /**
      * Uses {@link Hash} to choose a random (but stable) value from within this field.
      */
-    protected long doHash( int field ) {
+    protected long doHash(int step, int field) throws ANTLRException {
         int u = UPPER_BOUNDS[field];
         if (field==2) u = 28;   // day of month can vary depending on month, so to make life simpler, just use [1,28] that's always safe
         if (field==4) u = 6;   // Both 0 and 7 of day of week are Sunday. For better distribution, limit upper bound to 6
-        int h = hash.next(u+1 - LOWER_BOUNDS[field]); // upper bound is inclusive
-        return 1L << (h+LOWER_BOUNDS[field]);
+        return doHash(LOWER_BOUNDS[field], u, step);
     }
 
-    protected long doHash( int s, int e ) {
-        return 1L << (s+hash.next(e+1-s));
+    protected long doHash(int s, int e, int step) throws ANTLRException {
+        if (step > e - s + 1) {
+            error(Messages.BaseParser_OutOfRange(step, 1, e - s + 1));
+            throw new AssertionError();
+        } else if (step > 1) {
+            long bits = 0;
+            for (int i = hash.next(step) + s; i <= e; i += step) {
+                bits |= 1L << i;
+            }
+            assert bits != 0;
+            return bits;
+        } else if (step <=0) {
+            error(Messages.BaseParser_MustBePositive(step));
+            throw new AssertionError();
+        } else {
+            // step=1 (i.e. omitted) in the case of hash is actually special; means pick one value, not step by 1
+            return 1L << (s+hash.next(e+1-s));
+        }
     }
     
     protected void rangeCheck(int value, int field) throws ANTLRException {

core/src/main/resources/hudson/triggers/TimerTrigger/help-spec.html

@@ -45,6 +45,9 @@
   </p><p>
     The 'H' token can be used with a range. For example, '<tt>H H(0-7) * * *</tt>'
     means some time between midnight to 7:59am.
+    You can also use skips with 'H', with or without ranges.
+    For example, '<tt>H/15 * * * *</tt>' means every fifteen minutes (perhaps at :07, :22, :37, :52);
+    '<tt>H(0-29)/10 * * * *</tt>' means every ten minutes in the first half of every hour (perhaps at :04, :14, :24).
   </p><p>
     The '<tt>H</tt>' token can be thought of as a random value over a range,
     but it actually is a hash of the job name, not a random function, so that

core/src/test/java/hudson/scheduler/CronTabTest.java

@@ -188,7 +188,7 @@ public class CronTabTest {
 
     @Test
     public void testHash1() throws Exception {
-        CronTab x = new CronTab("H H(5-8) * * *",new Hash() {
+        CronTab x = new CronTab("H H(5-8) H/3 H(1-10)/4 *",new Hash() {
             public int next(int n) {
                 return n-1;
             }
@@ -196,6 +196,8 @@ public class CronTabTest {
 
         assertEquals("59;", bitset(x.bits[0]));
         assertEquals("8;", bitset(x.bits[1]));
+        assertEquals("3;6;9;12;15;18;21;24;27;", bitset(x.bits[2]));
+        assertEquals("4;8;", bitset(x.bits[3]));
     }
 
     private static String bitset(long bits) {
@@ -210,7 +212,7 @@ public class CronTabTest {
 
     @Test
     public void testHash2() throws Exception {
-        CronTab x = new CronTab("H H(5-8) * * *",new Hash() {
+        CronTab x = new CronTab("H H(5-8) H/3 H(1-10)/4 *",new Hash() {
             public int next(int n) {
                 return 1;
             }
@@ -218,6 +220,8 @@ public class CronTabTest {
 
         assertEquals("1;", bitset(x.bits[0]));
         assertEquals("6;", bitset(x.bits[1]));
+        assertEquals("2;5;8;11;14;17;20;23;26;", bitset(x.bits[2]));
+        assertEquals("2;6;10;", bitset(x.bits[3]));
     }
 
     @Test public void hashedMinute() throws Exception {
@@ -229,4 +233,20 @@ public class CronTabTest {
         compare(new GregorianCalendar(2013, 2, 22, 13, 56), new CronTab("H H(12-13) * * *", Hash.from("stuff")).ceil(t));
     }
 
+    @Test public void hashSkips() throws Exception {
+        compare(new GregorianCalendar(2013, 2, 21, 16, 26), new CronTab("H/15 * * * *", Hash.from("stuff")).ceil(new GregorianCalendar(2013, 2, 21, 16, 21)));
+        compare(new GregorianCalendar(2013, 2, 21, 16, 41), new CronTab("H/15 * * * *", Hash.from("stuff")).ceil(new GregorianCalendar(2013, 2, 21, 16, 31)));
+        compare(new GregorianCalendar(2013, 2, 21, 16, 56), new CronTab("H/15 * * * *", Hash.from("stuff")).ceil(new GregorianCalendar(2013, 2, 21, 16, 42)));
+        compare(new GregorianCalendar(2013, 2, 21, 17, 11), new CronTab("H/15 * * * *", Hash.from("stuff")).ceil(new GregorianCalendar(2013, 2, 21, 16, 59)));
+        compare(new GregorianCalendar(2013, 2, 21, 0, 2), new CronTab("H(0-15)/3 * * * *", Hash.from("junk")).ceil(new GregorianCalendar(2013, 2, 21, 0, 0)));
+        compare(new GregorianCalendar(2013, 2, 21, 0, 2), new CronTab("H(0-3)/4 * * * *", Hash.from("junk")).ceil(new GregorianCalendar(2013, 2, 21, 0, 0)));
+        compare(new GregorianCalendar(2013, 2, 21, 1, 2), new CronTab("H(0-3)/4 * * * *", Hash.from("junk")).ceil(new GregorianCalendar(2013, 2, 21, 0, 5)));
+        try {
+            compare(new GregorianCalendar(2013, 2, 21, 0, 0), new CronTab("H(0-3)/15 * * * *", Hash.from("junk")).ceil(new GregorianCalendar(2013, 2, 21, 0, 0)));
+            fail();
+        } catch (ANTLRException x) {
+            // good
+        }
+    }
+
 }