Add mutex initializer for wasm-c-api engine operations (#1656)

The host embedder may new/delete wasm-c-api engine simultaneously
in multiple threads, which requires lock for the operations. Since there
isn't one time called global init/destroy APIs provided by wasm-c-api,
we define a global lock and initialize it with thread mutex initializer if
the platform supports that, and use it to lock the operations of engine.

If the platform doesn't support thread mutex initializer, we require
developer to create the lock by himself to ensure the thread-safe of the
engine operations.

core/iwasm/common/wasm_c_api.c

@@ -327,45 +327,77 @@ wasm_engine_new_internal(mem_alloc_type_t type, const MemAllocOption *opts)
 
 /* global engine instance */
 static wasm_engine_t *singleton_engine = NULL;
+#if defined(OS_THREAD_MUTEX_INITIALIZER)
+/**
+ * lock for the singleton_engine
+ * Note: if the platform has mutex initializer, we use a global lock to
+ * lock the operations of the singleton_engine, otherwise when there are
+ * operations happening simultaneously in multiple threads, developer
+ * must create the lock by himself, and use it to lock the operations
+ */
+static korp_mutex engine_lock = OS_THREAD_MUTEX_INITIALIZER;
+#endif
+
+own wasm_engine_t *
+wasm_engine_new_with_args(mem_alloc_type_t type, const MemAllocOption *opts)
+{
+#if defined(OS_THREAD_MUTEX_INITIALIZER)
+    os_mutex_lock(&engine_lock);
+#endif
+
+    if (!singleton_engine) {
+        singleton_engine = wasm_engine_new_internal(type, opts);
+    }
+
+    if (singleton_engine) {
+        singleton_engine->ref_count++;
+    }
+
+#if defined(OS_THREAD_MUTEX_INITIALIZER)
+    os_mutex_unlock(&engine_lock);
+#endif
+
+    return singleton_engine;
+}
 
 own wasm_engine_t *
 wasm_engine_new()
 {
-    if (!singleton_engine) {
-        singleton_engine =
-            wasm_engine_new_internal(Alloc_With_System_Allocator, NULL);
-    }
-    if (singleton_engine)
-        singleton_engine->ref_count++;
-    return singleton_engine;
+    return wasm_engine_new_with_args(Alloc_With_System_Allocator, NULL);
 }
 
 own wasm_engine_t *
 wasm_engine_new_with_config(own wasm_config_t *config)
 {
     (void)config;
-    return wasm_engine_new();
+    return wasm_engine_new_with_args(Alloc_With_System_Allocator, NULL);
 }
 
-own wasm_engine_t *
-wasm_engine_new_with_args(mem_alloc_type_t type, const MemAllocOption *opts)
-{
-    if (!singleton_engine) {
-        singleton_engine = wasm_engine_new_internal(type, opts);
-    }
-    if (singleton_engine)
-        singleton_engine->ref_count++;
-    return singleton_engine;
-}
-
-/* BE AWARE: will RESET the singleton */
 void
 wasm_engine_delete(wasm_engine_t *engine)
 {
-    if (engine && (--engine->ref_count == 0)) {
-        wasm_engine_delete_internal(engine);
-        singleton_engine = NULL;
+#if defined(OS_THREAD_MUTEX_INITIALIZER)
+    os_mutex_lock(&engine_lock);
+#endif
+
+    if (!engine || !singleton_engine || engine != singleton_engine) {
+#if defined(OS_THREAD_MUTEX_INITIALIZER)
+        os_mutex_unlock(&engine_lock);
+#endif
+        return;
     }
+
+    if (singleton_engine->ref_count > 0) {
+        singleton_engine->ref_count--;
+        if (singleton_engine->ref_count == 0) {
+            wasm_engine_delete_internal(engine);
+            singleton_engine = NULL;
+        }
+    }
+
+#if defined(OS_THREAD_MUTEX_INITIALIZER)
+    os_mutex_unlock(&engine_lock);
+#endif
 }
 
 wasm_store_t *

core/iwasm/common/wasm_c_api_internal.h

@@ -27,7 +27,7 @@ WASM_DECLARE_VEC(store, *)
 struct wasm_engine_t {
     /* support one store for now */
     wasm_store_vec_t *stores;
-    uint32_t ref_count;
+    uint32 ref_count;
 };
 
 struct wasm_store_t {

core/iwasm/include/wasm_c_api.h

@@ -145,6 +145,19 @@ WASM_API_EXTERN own wasm_config_t* wasm_config_new(void);
 
 WASM_DECLARE_OWN(engine)
 
+/**
+ * Create a new engine
+ *
+ * Note: for the engine new/delete operations, including this,
+ * wasm_engine_new_with_config, wasm_engine_new_with_args, and
+ * wasm_engine_delete, if the platform has mutex initializer,
+ * then they are thread-safe: we use a global lock to lock the
+ * operations of the engine. Otherwise they are not thread-safe:
+ * when there are engine new/delete operations happening
+ * simultaneously in multiple threads, developer must create
+ * the lock by himself, and add the lock when calling these
+ * functions.
+ */
 WASM_API_EXTERN own wasm_engine_t* wasm_engine_new(void);
 WASM_API_EXTERN own wasm_engine_t* wasm_engine_new_with_config(own wasm_config_t*);
 

core/shared/platform/android/platform_internal.h

@@ -57,6 +57,8 @@ typedef pthread_cond_t korp_cond;
 typedef pthread_t korp_thread;
 typedef sem_t korp_sem;
 
+#define OS_THREAD_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
+
 #define os_thread_local_attribute __thread
 
 #define bh_socket_t int

core/shared/platform/darwin/platform_internal.h

@@ -60,6 +60,8 @@ typedef pthread_cond_t korp_cond;
 typedef pthread_t korp_thread;
 typedef sem_t korp_sem;
 
+#define OS_THREAD_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
+
 #define os_thread_local_attribute __thread
 
 #define bh_socket_t int

core/shared/platform/esp-idf/platform_internal.h

@@ -41,6 +41,8 @@ typedef pthread_cond_t korp_cond;
 typedef pthread_t korp_thread;
 typedef unsigned int korp_sem;
 
+#define OS_THREAD_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
+
 #define BH_APPLET_PRESERVED_STACK_SIZE (2 * BH_KB)
 
 /* Default thread priority */

core/shared/platform/linux-sgx/platform_internal.h

@@ -52,6 +52,10 @@ typedef pthread_mutex_t korp_mutex;
 typedef pthread_cond_t korp_cond;
 typedef unsigned int korp_sem;
 
+#ifndef SGX_DISABLE_PTHREAD
+#define OS_THREAD_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
+#endif
+
 typedef int (*os_print_function_t)(const char *message);
 void
 os_set_print_function(os_print_function_t pf);

core/shared/platform/linux/platform_internal.h

@@ -57,6 +57,8 @@ typedef pthread_cond_t korp_cond;
 typedef pthread_t korp_thread;
 typedef sem_t korp_sem;
 
+#define OS_THREAD_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
+
 #define os_thread_local_attribute __thread
 
 #define bh_socket_t int

core/shared/platform/nuttx/platform_internal.h

@@ -42,6 +42,8 @@ typedef pthread_cond_t korp_cond;
 typedef pthread_t korp_thread;
 typedef sem_t korp_sem;
 
+#define OS_THREAD_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
+
 #define BH_APPLET_PRESERVED_STACK_SIZE (2 * BH_KB)
 
 /* Default thread priority */

core/shared/platform/vxworks/platform_internal.h

@@ -56,6 +56,8 @@ typedef pthread_cond_t korp_cond;
 typedef pthread_t korp_thread;
 typedef sem_t korp_sem;
 
+#define OS_THREAD_MUTEX_INITIALIZER PTHREAD_MUTEX_INITIALIZER
+
 #define os_thread_local_attribute __thread
 
 #if WASM_DISABLE_HW_BOUND_CHECK == 0

core/shared/platform/windows/platform_internal.h

@@ -56,6 +56,17 @@ typedef void *korp_tid;
 typedef void *korp_mutex;
 typedef void *korp_sem;
 
+/**
+ * Create the mutex when os_mutex_lock is called, and no need to
+ * CloseHandle() for the static lock's lifetime, since
+ * "The system closes the handle automatically when the process
+ *  terminates. The mutex object is destroyed when its last
+ *  handle has been closed."
+ * Refer to:
+ *   https://learn.microsoft.com/en-us/windows/win32/api/synchapi/nf-synchapi-createmutexa
+ */
+#define OS_THREAD_MUTEX_INITIALIZER NULL
+
 struct os_thread_wait_node;
 typedef struct os_thread_wait_node *os_thread_wait_list;
 typedef struct korp_cond {

core/shared/platform/windows/win_thread.c

@@ -512,6 +512,21 @@ os_mutex_lock(korp_mutex *mutex)
     int ret;
 
     assert(mutex);
+
+    if (*mutex == NULL) { /* static initializer? */
+        HANDLE p = CreateMutex(NULL, FALSE, NULL);
+
+        if (!p) {
+            return BHT_ERROR;
+        }
+
+        if (InterlockedCompareExchangePointer((PVOID *)mutex, (PVOID)p, NULL)
+            != NULL) {
+            /* lock has been created by other threads */
+            CloseHandle(p);
+        }
+    }
+
     ret = WaitForSingleObject(*mutex, INFINITE);
     return ret != WAIT_FAILED ? BHT_OK : BHT_ERROR;
 }