From cc6979ca4c81867baac0a0cd6e1db484fcd57c65 Mon Sep 17 00:00:00 2001
From: Laurent MAZET <laurent.mazet@thalesgroup.com>
Date: Fri, 3 Oct 2025 18:33:48 +0200
Subject: [PATCH] rework semaphore test

---
 mutex.c     |   1 +
 semaphore.c | 102 +++++++++++++++++++++++++++++++---------------------
 2 files changed, 62 insertions(+), 41 deletions(-)

diff --git a/mutex.c b/mutex.c
index 9d8a488..6dba569 100644
--- a/mutex.c
+++ b/mutex.c
@@ -25,6 +25,7 @@ int try = 0;
 int nbtoofast = 0;
 
 #define TIMER 1000
+
 void *mutex_giver_task (__attribute__((unused)) void *arg)
 {
 
diff --git a/semaphore.c b/semaphore.c
index 4bcd736..ac0202c 100644
--- a/semaphore.c
+++ b/semaphore.c
@@ -2,51 +2,71 @@
 /* cflags: */
 /* linker: mtime.o test.o stat.o -lm -lpthread -lrt */
 
-#include <pthread.h>
-#include <semaphore.h>
 #include <stdio.h>
 #include <string.h>
 
+#include <semaphore.h>
+
+#include <pthread.h>
+#include <unistd.h>
+
 #include "mtime.h"
 #include "test.h"
 
-#define NT 2
-
 /* global variables */
 
-dts_t *measure_tab = NULL;
+dts_t *deltas = NULL;
+int nb_measurements = 0;
 
-char *message = "semaphore";
+char *message = "Semaphore latency";
 void (*usage_ext) (FILE *) = NULL;
 int (*parse_arg_ext) (char *) = NULL;
 
-int counter = 0;
-int try = 0;
+pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
+volatile int shared_flag = 0;
+ts_t ts1, ts2;
 sem_t sem;
+int try = 0;
+int nbtoofast = 0;
 
-void* trythis (__attribute__((unused)) void *arg)
-{
-    sem_wait (&sem);
+#define TIMER 1000
 
-    static ts_t tsi;
-    ts_t ts;
-    sys_timestamp (&ts);
+void *semaphore_giver_task (__attribute__((unused)) void *arg)
+{
 
-    /* thread 1 took the lock -> timestamp 1 */
-    if (counter % 2 == 0) {
-        set_timestamp (&tsi, &ts);
+    while (try < nb_measurements) {
+        sem_wait (&sem);
+        usleep (TIMER);
+        shared_flag = 1;
+        sys_timestamp (&ts1);
+        sem_post (&sem);
+        //shared_flag = 0;
+        usleep (TIMER);
     }
 
-    /* thread 2 took the lock -> timestamp 2 */
-    else {
-        measure_tab[try++] = diff_timestamp (&ts, &tsi);
-    }
+    pthread_exit (NULL);
+}
 
-    counter += 1;
+void *semaphore_taker_task (__attribute__((unused)) void *arg)
+{
 
-    sem_post (&sem);
+    while (try < nb_measurements) {
+        ts_t ts;
+        sys_timestamp (&ts);
+        sem_wait (&sem);
+        if (shared_flag) {
+            sys_timestamp (&ts2);
+            if (diff_timestamp (&ts2, &ts) < (9 * TIMER / 10)) {
+                nbtoofast++;
+            } else {
+                deltas[try++] = diff_timestamp (&ts2, &ts1);
+            }
+            shared_flag = 0;
+        }
+        sem_post (&sem);
+    }
 
-    return NULL;
+    pthread_exit (NULL);
 }
 
 int test (dts_t *buffer, int nb)
@@ -54,33 +74,33 @@ int test (dts_t *buffer, int nb)
 
     /* set global variables */
 
-    measure_tab = buffer;
+    deltas = buffer;
+    nb_measurements = nb;
 
     /* semaphore test */
 
     sem_init (&sem, 0, 1);
 
-    for (int i = 0; i < nb; i++) {
-
-        //bzero (&tsi, sizeof (ts1));
+    shared_flag = 1;
 
-        pthread_t tid1;
-        if (pthread_create (&tid1, NULL, trythis, NULL) != 0) {
-            fprintf (stderr, "error on pthread_create\n");
-            return 1;
-        }
-
-        pthread_t tid2;
-        if (pthread_create (&tid2, NULL, trythis, NULL) != 0) {
-            fprintf (stderr, "error on pthread_create\n");
-            return 1;
-        }
+    pthread_t giver_thread;
+    if (pthread_create (&giver_thread, NULL, semaphore_giver_task, NULL) != 0) {
+        fprintf (stderr, "error on pthread_create for giver_task\n");
+        return 1;
+    }
 
-        pthread_join (tid1, NULL);
-        pthread_join (tid2, NULL);
+    pthread_t taker_thread;
+    if (pthread_create (&taker_thread, NULL, semaphore_taker_task, NULL) != 0) {
+        fprintf (stderr, "error on pthread_create for taker_task\n");
+        return 1;
     }
 
+    pthread_join (giver_thread, NULL);
+    pthread_join (taker_thread, NULL);
+
     sem_destroy (&sem);
 
+    printf ("Too fast: %d\n", nbtoofast);
+
     return 0;
 }
-- 
2.30.2