aprell · March 7, 2019 19:13 · Mar 7, 2019
diff --git a/Makefile b/Makefile
@@ -0,0 +1,13 @@
+CC := gcc
+CFLAGS += -Wall -Wextra -std=c99
+LDLIBS += -lpthread
+
+all: test_wrap
+
+test_wrap: LDFLAGS += -Wl,--wrap=pthread_create -Wl,--wrap=pthread_join
+test_wrap: test_wrap.c wrap.c
+
+clean:
+	rm -rf test_wrap
+
+.PHONY: all clean
diff --git a/test_wrap.c b/test_wrap.c
@@ -0,0 +1,34 @@
+#include <assert.h>
+#include <pthread.h>
+#include <stdlib.h>
+
+unsigned int num_threads;
+
+static void *thread_entry_fn(void *arg)
+{
+    (void)arg;
+    return NULL;
+}
+
+int main(int argc, char *argv[])
+{
+    unsigned int n = argc > 1 && atoi(argv[1]) >= 0 ? atoi(argv[1]) : 4;
+    pthread_t *threads = malloc(n * sizeof(pthread_t));
+    if (!threads) return EXIT_FAILURE;
+
+    for (unsigned int i = 0; i < n; i++) {
+        pthread_create(&threads[i], NULL, thread_entry_fn, NULL);
+    }
+
+    assert(num_threads == n);
+
+    for (unsigned int i = 0; i < n; i++) {
+        pthread_join(threads[i], NULL);
+    }
+
+    assert(num_threads == 0);
+
+    free(threads);
+
+    return 0;
+}
diff --git a/wrap.c b/wrap.c
@@ -0,0 +1,26 @@
+#include <pthread.h>
+
+extern unsigned int num_threads;
+
+// From the docs:
+// Any undefined reference to `symbol` will be resolved to `__wrap_symbol`. Any
+// undefined reference to `__real_symbol` will be resolved to `symbol`. This
+// can be used to provide a wrapper for a system function. The wrapper function
+// should be called `__wrap_symbol`. If it wishes to call the system function,
+// it should call `__real_symbol`.
+
+extern int __real_pthread_create(pthread_t *, const pthread_attr_t *, void *(*)(void *), void *);
+
+extern int __real_pthread_join(pthread_t, void **);
+
+int __wrap_pthread_create(pthread_t *thread, const pthread_attr_t *attr, void *(*start_routine)(void *), void *arg)
+{
+    num_threads++;
+    return __real_pthread_create(thread, attr, start_routine, arg);
+}
+
+int __wrap_pthread_join(pthread_t thread, void **retval)
+{
+    num_threads--;
+    return __real_pthread_join(thread, retval);
+}
No results found