3.x: Allow setting the drift tolerance timeunit via system property

src/main/java/io/reactivex/rxjava3/core/Scheduler.java

@@ -73,8 +73,8 @@
  * based on the relative time between it and {@link Worker#now(TimeUnit)}. However, drifts or changes in the
  * system clock could affect this calculation either by scheduling subsequent runs too frequently or too far apart.
  * Therefore, the default implementation uses the {@link #clockDriftTolerance()} value (set via
- * {@code rx3.scheduler.drift-tolerance} in minutes) to detect a drift in {@link Worker#now(TimeUnit)} and
- * re-adjust the absolute/relative time calculation accordingly.
+ * {@code rx3.scheduler.drift-tolerance} and {@code rx3.scheduler.drift-tolerance-unit}) to detect a
+ * drift in {@link Worker#now(TimeUnit)} and re-adjust the absolute/relative time calculation accordingly.
  * <p>
  * The default implementations of {@link #start()} and {@link #shutdown()} do nothing and should be overridden if the
  * underlying task-execution scheme supports stopping and restarting itself.
@@ -91,17 +91,42 @@ public abstract class Scheduler {
     /**
      * The tolerance for a clock drift in nanoseconds where the periodic scheduler will rebase.
      * <p>
-     * The associated system parameter, {@code rx3.scheduler.drift-tolerance}, expects its value in minutes.
+     * Associated system parameters:
+     * <ul>
+     * <li>{@code rx3.scheduler.drift-tolerance}, long, default {@code 15}</li>
+     * <li>{@code rx3.scheduler.drift-tolerance-unit}, string, default {@code minutes},
+     *     supports {@code seconds} and {@code milliseconds}.
+     * </ul>
      */
-    static final long CLOCK_DRIFT_TOLERANCE_NANOSECONDS;
-    static {
-        CLOCK_DRIFT_TOLERANCE_NANOSECONDS = TimeUnit.MINUTES.toNanos(
-                Long.getLong("rx3.scheduler.drift-tolerance", 15));
+    static final long CLOCK_DRIFT_TOLERANCE_NANOSECONDS =
+            computeClockDrift(
+                    Long.getLong("rx3.scheduler.drift-tolerance", 15),
+                    System.getProperty("rx3.scheduler.drift-tolerance-unit", "minutes")
+            );
+
+    /**
+     * Returns the clock drift tolerance in nanoseconds based on the input selection.
+     * @param time the time value
+     * @param timeUnit the time unit string
+     * @return the time amount in nanoseconds
+     */
+    static long computeClockDrift(long time, String timeUnit) {
+        if ("seconds".equalsIgnoreCase(timeUnit)) {
+            return TimeUnit.SECONDS.toNanos(time);
+        } else if ("milliseconds".equalsIgnoreCase(timeUnit)) {
+            return TimeUnit.MILLISECONDS.toNanos(time);
+        }
+        return TimeUnit.MINUTES.toNanos(time);
     }
 
     /**
      * Returns the clock drift tolerance in nanoseconds.
-     * <p>Related system property: {@code rx3.scheduler.drift-tolerance} in minutes.
+     * <p>Related system properties:
+     * <ul>
+     * <li>{@code rx3.scheduler.drift-tolerance}, long, default {@code 15}</li>
+     * <li>{@code rx3.scheduler.drift-tolerance-unit}, string, default {@code minutes},
+     *     supports {@code seconds} and {@code milliseconds}.
+     * </ul>
      * @return the tolerance in nanoseconds
      * @since 2.0
      */
@@ -350,7 +375,7 @@ public <S extends Scheduler & Disposable> S when(@NonNull Function<Flowable<Flow
      * based on the relative time between it and {@link #now(TimeUnit)}. However, drifts or changes in the
      * system clock would affect this calculation either by scheduling subsequent runs too frequently or too far apart.
      * Therefore, the default implementation uses the {@link #clockDriftTolerance()} value (set via
-     * {@code rx3.scheduler.drift-tolerance} in minutes) to detect a drift in {@link #now(TimeUnit)} and
+     * {@code rx3.scheduler.drift-tolerance} and {@code rx3.scheduler.drift-tolerance-unit}) to detect a drift in {@link #now(TimeUnit)} and
      * re-adjust the absolute/relative time calculation accordingly.
      * <p>
      * If the {@code Worker} is disposed, the {@code schedule} methods

src/test/java/io/reactivex/rxjava3/core/SchedulerTest.java

@@ -0,0 +1,37 @@
+/**
+ * Copyright (c) 2016-present, RxJava Contributors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.reactivex.rxjava3.core;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+public class SchedulerTest {
+
+    @Test
+    public void clockDriftCalculation() {
+        assertEquals(100_000_000L, Scheduler.computeClockDrift(100, "milliseconds"));
+
+        assertEquals(2_000_000_000L, Scheduler.computeClockDrift(2, "seconds"));
+
+        assertEquals(180_000_000_000L, Scheduler.computeClockDrift(3, "minutes"));
+
+        assertEquals(240_000_000_000L, Scheduler.computeClockDrift(4, "random"));
+
+        assertEquals(300_000_000_000L, Scheduler.computeClockDrift(5, null));
+    }
+
+}