1 files changed, 55 insertions, 0 deletions
diff --git a/jdisc_core/src/main/java/com/yahoo/jdisc/TimeBudget.java b/jdisc_core/src/main/java/com/yahoo/jdisc/TimeBudget.java
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+++ b/jdisc_core/src/main/java/com/yahoo/jdisc/TimeBudget.java
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+// Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.jdisc;
+
+import javax.annotation.concurrent.Immutable;
+import java.time.Duration;
+import java.time.Instant;
+
+/**
+ * A TimeBudget tracks the current time compared to a start time and deadline.
+ *
+ * @author hakon
+ */
+@Immutable
+public class TimeBudget {
+    private final Timer timer;
+    private final Instant start;
+    private final Duration timeout;
+
+    /** Returns a TimeBudget with a start time of now, and with the given timeout. */
+    public static TimeBudget fromNow(Timer timer, Duration timeout) {
+        return new TimeBudget(timer, timer.currentTime(), timeout);
+    }
+
+    private TimeBudget(Timer timer, Instant start, Duration timeout) {
+        this.timer = timer;
+        this.start = start;
+        this.timeout = timeout;
+    }
+
+    /** Time until 'headroom' before deadline. Guaranteed to be non-negative. */
+    public Duration timeBeforeDeadline(Duration headroom) {
+        return nonNegativeBetween(now(), deadline().minus(headroom));
+    }
+
+    /** Returns the original timeout. */
+    public Duration originalTimeout() {
+        return timeout;
+    }
+
+    private static Duration nonNegativeBetween(Instant start, Instant end) {
+        return makeNonNegative(Duration.between(start, end));
+    }
+
+    private static Duration makeNonNegative(Duration duration) {
+        return duration.isNegative() ? Duration.ZERO : duration;
+    }
+
+    private Instant now() {
+        return timer.currentTime();
+    }
+
+    private Instant deadline() {
+        return start.plus(timeout);
+    }
+}