From f5b3a7a87e028fe1630d0abbbe82c1abcacdd969 Mon Sep 17 00:00:00 2001
From: Alessandre Laguierce <alessandre.laguierce@enseirb-matmeca.fr>
Date: Thu, 20 Mar 2025 19:43:00 +0100
Subject: [PATCH] feat: first version, just want to beat M. Faverge on the
 leaderboard for the first benchmark

---
 Makefile            |   7 +++
 src/thread/thread.c | 102 ++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 101 insertions(+), 8 deletions(-)

diff --git a/Makefile b/Makefile
index 6bb380e..818dcfb 100644
--- a/Makefile
+++ b/Makefile
@@ -38,6 +38,9 @@ ifdef USE_PTHREAD
 LDFLAGS+=-lpthread
 CFLAGS+=-DUSE_PTHREAD
 endif
+ifndef USE_DEBUG
+CFLAGS+=-DNDEBUG
+endif
 
 # Tests if the last compilation was with pthread
 ifeq ("$(wildcard .lastpthread)","")
@@ -84,6 +87,10 @@ ${valgrind_targets}: valgrind_%: ${build_dir}/%
 .PHONY: build
 build: ${bins_target} ${build_dir}/libthread.so ${build_dir}/libthread.a
 
+.PHONY: debug
+debug:
+	$(MAKE) USE_DEBUG=. build
+
 .PHONY: pthreads
 pthreads:
 	$(MAKE) USE_PTHREAD=. ${pthread_targets}
diff --git a/src/thread/thread.c b/src/thread/thread.c
index 2b24486..3fbf083 100644
--- a/src/thread/thread.c
+++ b/src/thread/thread.c
@@ -3,32 +3,118 @@
 #include "thread.h"
 #include "debug.h"
 #include "pthread.h"
+#include <sys/queue.h>
 #include <bits/pthreadtypes.h>
-#include <sched.h>
+#include <stdlib.h>
+#include <ucontext.h>
 
+#ifndef STACK_SIZE
+#define STACK_SIZE 4096*4
+#endif
+
+struct context_entry {
+  ucontext_t context;
+  thread_t id;
+  thread_t parent;
+  int finished;
+  void *retvalue;
+  TAILQ_ENTRY(context_entry) link;
+};
+
+static TAILQ_HEAD(context_head, context_entry) head = TAILQ_HEAD_INITIALIZER(head);
+static struct context_entry *running = 0;
+static unsigned long long counter = 0;
 
 int thread_yield(void) {
-  return sched_yield();
+  if (counter <= 1) {
+    return 0;
+  }
+  struct context_entry *first;
+  do  {
+    first = TAILQ_FIRST(&head);
+    if (!first) {
+      return -1;
+    }
+    if (first->id == running->id) {
+      return 0;
+    }
+    TAILQ_REMOVE(&head, first, link);
+    TAILQ_INSERT_TAIL(&head, first, link);
+  } while (first->finished);
+  struct context_entry *old_runner = running;
+  running = first;
+  swapcontext(&old_runner->context, &running->context);
+  return 0;
 }
 
-
 thread_t thread_self(void) {
-return (void *) pthread_self();
+  if (running == NULL) {
+    return 0;
+  }
+  return running->id;
 }
 
 int thread_create(thread_t *newthread, void *(*func)(void *), void *funcarg) {
   TRACE("Create a new thread that execute function %p", func);
-  return pthread_create((pthread_t *) newthread, NULL, func, funcarg);
+  if (counter == 0) {
+    struct context_entry *main = malloc(sizeof(*main));
+    getcontext(&main->context);
+    main->id = 0;
+    TAILQ_INSERT_HEAD(&head, main, link);
+    running = main;
+    counter++;
+  }
+  struct context_entry *new_entry = malloc(sizeof(*new_entry));
+  getcontext(&new_entry->context);
+  new_entry->context.uc_stack.ss_sp = malloc(STACK_SIZE);
+  new_entry->context.uc_stack.ss_size = STACK_SIZE;
+  new_entry->id = new_entry;
+  new_entry->parent = running->id;
+  new_entry->finished = 0;
+  new_entry->retvalue = 0;
+  *newthread = new_entry;
+  makecontext(&new_entry->context, (void (*)()) func, 1, funcarg);
+  counter++;
+  TAILQ_INSERT_HEAD(&head, new_entry, link);
+  return 0;
+}
+
+void print_entry(struct context_entry *entry) {
+  TRACE("CONTEXT (%p, %p, %d, %p);\n", entry, entry->id, entry->finished, entry->parent);
 }
 
 int thread_join(thread_t thread, void **retval) {
   TRACE("Join thread %p", thread);
-  return pthread_join((pthread_t) thread, retval);
+  struct context_entry *entry;
+  TAILQ_FOREACH(entry, &head, link) {
+    if (entry->id != thread) {
+      continue;
+    }
+    while (!entry->finished) {
+      thread_yield();
+    }
+    if (retval)
+      *retval = entry->retvalue;
+    TAILQ_REMOVE(&head, entry, link);
+    free(entry->context.uc_stack.ss_sp);
+    free(entry);
+    if (--counter == 1) {
+      TAILQ_REMOVE(&head, running, link);
+      free(running->context.uc_stack.ss_sp);
+      free(running);
+      running = 0;
+      counter = 0;
+    }
+    return 0;
+  }
+  return -1;
 }
 
 void thread_exit(void *retval) {
-  TRACE("Exit thread");
-  pthread_exit(retval);
+  TRACE("Exit thread %p", running);
+  running->finished = 1;
+  running->retvalue = retval;
+  thread_yield();
 }
 
 int thread_mutex_init(thread_mutex_t *mutex) {