diff --git a/include/pandio/core.h b/include/pandio/core.h
index be09bef..b90fba2 100644
--- a/include/pandio/core.h
+++ b/include/pandio/core.h
@@ -16,9 +16,12 @@ typedef HMODULE pd_dlib_t;
 typedef CRITICAL_SECTION pd_mutex_t;
 typedef CONDITION_VARIABLE pd_cond_t;
 typedef HANDLE pd_thread_t;
+typedef INIT_ONCE pd_once_t;
 typedef DWORD pd_errno_t;   // system error type
 typedef DWORD pd_pid_t;
 
+#define PD_ONCE_INIT INIT_ONCE_STATIC_INIT
+
 #else
 #include <pthread.h>
 #include <errno.h>
@@ -29,8 +32,11 @@ typedef void* pd_dlib_t;
 typedef pthread_mutex_t pd_mutex_t;
 typedef pthread_cond_t pd_cond_t;
 typedef pthread_t pd_thread_t;
+typedef pthread_once_t pd_once_t;
 typedef int pd_errno_t;   // system error type
 typedef pid_t pd_pid_t;
+
+#define PD_ONCE_INIT PTHREAD_ONCE_INIT
 #endif
 
 int pd_random(void *, size_t);
@@ -59,6 +65,9 @@ void pd_thread_create(pd_thread_t*, void* (*)(void*), void *);
 
 void pd_thread_join(pd_thread_t*);
 
+/* call specific function only once in multithreaded environment */
+int pd_once(pd_once_t*, void (*)(void));
+
 struct pd_notifier_s;
 
 struct pd_io_s {
diff --git a/samples/random.c b/samples/random.c
index a4edc1b..c058062 100644
--- a/samples/random.c
+++ b/samples/random.c
@@ -3,6 +3,13 @@
 
 #define n 16
 
+void print_bytes(unsigned char *bytes, size_t size) {
+    for (size_t i = 0; i < size; i++) {
+        printf("%02x ", bytes[i]);
+    }
+    printf("\n");
+}
+
 int main() {
     unsigned char buf[n];
     int status = pd_random(buf, 16);
@@ -12,10 +19,15 @@ int main() {
         return 1;
     }
 
-    for (size_t i = 0; i < n; i++) {
-        printf("%02x ", buf[i]);
+    print_bytes(buf, n);
+
+    unsigned char *buf2 = malloc(sizeof(unsigned char) * n);
+    if ((status = pd_random(buf2, n)) == 0) {
+        print_bytes(buf2, n);
+    } else {
+        printf("error: %s\n", pd_errstr(status));
+        return 1;
     }
-    printf("\n");
 
     return 0;
 }
diff --git a/src/random.c b/src/random.c
index 8760e67..790a90c 100644
--- a/src/random.c
+++ b/src/random.c
@@ -26,21 +26,14 @@
 
 HCRYPTPROV hProv = 0;
 
-bool initialized = false;
-int pd__init_random_once() {
-    if (initialized)
-        return 0;
-
-    initialized = true;
-    if (!CryptAcquireContext(&hProv, NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT)) {
-        return -1;
-    }
-
-    return 0;
+pd_once_t init_control = PD_ONCE_INIT;
+void pd__init_random_once(void) {
+    // TODO: handle this error
+    CryptAcquireContext(&hProv, NULL, NULL, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT);
 }
 
 int pd_random(void *bytes, size_t size) {
-    if (pd__init_random_once() == -1)
+    if (pd_once(&init_control, pd__init_random_once) == -1)
         return PD_UNKNOWN;
 
     if (size == 0)
@@ -60,6 +53,7 @@ int pd_random(void *bytes, size_t size) {
     if (size == 0)
         return 0;
 
+    // TODO: maybe use pd_once as well to get fd only once?
     int fd = open("/dev/urandom", O_RDONLY);
     if (fd == -1) {
         return pd_errno();
diff --git a/src/sys/thread_unix.c b/src/sys/thread_unix.c
index 9b78231..6a6e705 100644
--- a/src/sys/thread_unix.c
+++ b/src/sys/thread_unix.c
@@ -87,3 +87,11 @@ void pd_thread_create(pd_thread_t *thread, void* (func)(void*), void *args) {
 void pd_thread_join(pd_thread_t *thread) {
     pthread_join(*thread, NULL);
 }
+
+int pd_once(pd_once_t *once_control, void (*init_routine)(void)) {
+    int errcode = pthread_once(once_control, init_routine);
+    if (errcode)
+        return pd_errmap(errcode);
+
+    return 0;
+}
diff --git a/src/sys/thread_win32.c b/src/sys/thread_win32.c
index 7b4c03e..e31aeac 100644
--- a/src/sys/thread_win32.c
+++ b/src/sys/thread_win32.c
@@ -20,6 +20,7 @@
  */
 
 #include "pandio/core.h"
+#include "pandio/err.h"
 #include <process.h>
 
 
@@ -108,3 +109,16 @@ void pd_thread_create(pd_thread_t *thread, void* (func)(void*), void *arg) {
 void pd_thread_join(pd_thread_t *thread) {
     WaitForSingleObject(*thread, INFINITE);
 }
+
+BOOL pd__init_once(PINIT_ONCE InitOnce, PVOID Parameter, PVOID *Context) {
+    void (*init_routine)(void) = Parameter;
+    init_routine();
+    return TRUE;
+}
+
+int pd_once(pd_once_t *once_control, void (*init_routine)(void)) {
+    if (InitOnceExecuteOnce(once_control, pd__init_once, init_routine, NULL))
+        return 0;
+
+    return pd_errno();
+}