From 867136ff1bca4e551a0180e9015309902cc70601 Mon Sep 17 00:00:00 2001
From: Andrew Noyes <andrew@weaselab.dev>
Date: Mon, 9 Sep 2024 21:59:49 -0700
Subject: [PATCH] Return pointer to next function

---
 InterleavingTest.cpp | 34 ++++++++++++++++++++--------------
 1 file changed, 20 insertions(+), 14 deletions(-)

diff --git a/InterleavingTest.cpp b/InterleavingTest.cpp
index 035a700..dbc166a 100644
--- a/InterleavingTest.cpp
+++ b/InterleavingTest.cpp
@@ -8,16 +8,18 @@
 
 struct Job {
   int *input;
-  bool (*next)(Job *);
+  // Returned void* is a function pointer to the next continuation. We have to
+  // use void* because otherwise the type would be recursive.
+  typedef void *(*continuation)(Job *);
+  continuation next;
 };
 
-bool stepJob(Job *j) {
-  auto &val = *j->input;
-  auto result = --val == 0;
+void *stepJob(Job *j) {
+  auto done = --(*j->input) == 0;
 #ifdef __x86_64__
   _mm_clflush(j->input);
 #endif
-  return result;
+  return done ? nullptr : (void *)stepJob;
 }
 
 // So we can look at the disassembly more easily
@@ -25,14 +27,15 @@ bool stepJob(Job *j) {
 extern "C" {
 void sequential(Job **jobs, int count) {
   for (int i = 0; i < count; ++i) {
-    while (!jobs[i]->next(jobs[i]))
-      ;
+    do {
+      jobs[i]->next = (Job::continuation)jobs[i]->next(jobs[i]);
+    } while (jobs[i]->next);
   }
 }
 
 void sequentialNoFuncPtr(Job **jobs, int count) {
   for (int i = 0; i < count; ++i) {
-    while (!stepJob(jobs[i]))
+    while (stepJob(jobs[i]))
       ;
   }
 }
@@ -40,8 +43,9 @@ void sequentialNoFuncPtr(Job **jobs, int count) {
 void interleaveSwapping(Job **jobs, int remaining) {
   int current = 0;
   while (remaining > 0) {
-    bool done = jobs[current]->next(jobs[current]);
-    if (done) {
+    auto next = (Job::continuation)jobs[current]->next(jobs[current]);
+    jobs[current]->next = next;
+    if (next == nullptr) {
       jobs[current] = jobs[remaining - 1];
       --remaining;
     } else {
@@ -72,8 +76,9 @@ void interleaveBoundedCyclicList(Job **jobs, int count) {
   int prevJob = started - 1;
   int job = 0;
   for (;;) {
-    bool done = inProgress[job]->next(inProgress[job]);
-    if (done) {
+    auto next = (Job::continuation)inProgress[job]->next(inProgress[job]);
+    inProgress[job]->next = next;
+    if (next == nullptr) {
       if (started == count) {
         if (prevJob == job)
           break;
@@ -100,8 +105,9 @@ void interleaveCyclicList(Job **jobs, int count) {
   int prevJob = count - 1;
   int job = 0;
   for (;;) {
-    bool done = jobs[job]->next(jobs[job]);
-    if (done) {
+    auto next = (Job::continuation)jobs[job]->next(jobs[job]);
+    jobs[job]->next = next;
+    if (next == nullptr) {
       if (prevJob == job)
         break;
       nextJob[prevJob] = nextJob[job];