From 5645d87eb165be79d49d54cd9ccdce921c5229a9 Mon Sep 17 00:00:00 2001
From: Martin Kinkelin <noone@nowhere.com>
Date: Wed, 30 Nov 2022 22:31:57 +0100
Subject: [PATCH] Fix Issue 22745 - std.parallelism.parallel fails to process
 empty range on a single CPU

---
 std/parallelism.d | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/std/parallelism.d b/std/parallelism.d
index 2c976388d..bab394a6b 100644
--- a/std/parallelism.d
+++ b/std/parallelism.d
@@ -1508,7 +1508,7 @@ public:
 
         if (this.size == 0)
         {
-            return rangeLen;
+            return max(rangeLen, 1);
         }
 
         immutable size_t eightSize = 4 * (this.size + 1);
@@ -3644,6 +3644,15 @@ ParallelForeach!R parallel(R)(R range, size_t workUnitSize)
     assert(arrIndex.sum == 10.iota.sum);
 }
 
+// https://issues.dlang.org/show_bug.cgi?id=22745
+@system unittest
+{
+    auto pool = new TaskPool(0);
+    int[] empty;
+    foreach (i; pool.parallel(empty)) {}
+    pool.finish();
+}
+
 // Thrown when a parallel foreach loop is broken from.
 class ParallelForeachError : Error
 {