Adjust mutex test

tests/stdio/mutex.c

@@ -1,30 +1,47 @@
 #include <stdio.h>
 #include <stdlib.h>
+#include <pthread.h>
 
 #include "test_helpers.h"
 
-int main(void) {
-    FILE *f = fopen("stdio/stdio.in", "r");
-    ERROR_IF(fopen, f, == NULL);
+FILE *f;
 
-    flockfile(f);
+void* thread_wontlock(void* arg) {
+    (void)arg;
 
-    // Commenting this out should cause a deadlock:
-    // flockfile(f);
+    int result = ftrylockfile(f);
+    UNEXP_IF(ftrylockfile, result, == 0);
 
-    if (!ftrylockfile(f)) {
-        puts("Mutex unlocked but it shouldn't be");
-        exit(EXIT_FAILURE);
-    }
-    funlockfile(f);
-
-    if (ftrylockfile(f)) {
-        puts("Mutex locked but it shouldn't be");
-        exit(EXIT_FAILURE);
-    }
-    if (!ftrylockfile(f)) {
-        puts("Mutex unlocked but it shouldn't be");
-        exit(EXIT_FAILURE);
-    }
-    funlockfile(f);
+    return NULL;
+}
+
+void* thread_willlock(void* arg) {
+    (void)arg;
+
+    int result = ftrylockfile(f);
+    UNEXP_IF(ftrylockfile, result, != 0);
+
+    return NULL;
+}
+
+int main(void) {
+    f = fopen("stdio/stdio.in", "r");
+    ERROR_IF(fopen, f, == NULL);
+    flockfile(f);
+    flockfile(f);
+    thread_willlock(NULL);
+
+    pthread_t thread;
+    for (int i = 1; i <= 3; i++) {
+        pthread_create(&thread, NULL, thread_wontlock, NULL);
+        pthread_join(thread, NULL);
+        funlockfile(f);
+    }
+
+    pthread_create(&thread, NULL, thread_willlock, NULL);
+    pthread_join(thread, NULL);
+
+    // TODO: glibc refuses to quit test without this
+    //       but in relibc, it will result in EPERM
+    // funlockfile(f);
 }