Modules TSC: GIL and cooperative multi tasking setup.

src/module.c

@@ -105,7 +105,7 @@ struct RedisModuleCtx {
     int flags;                      /* REDISMODULE_CTX_... flags. */
     void **postponed_arrays;        /* To set with RM_ReplySetArrayLength(). */
     int postponed_arrays_count;     /* Number of entries in postponed_arrays. */
-    void *blocked_privdata;         /* Privdata set when unblocking a clinet. */
+    void *blocked_privdata;         /* Privdata set when unblocking a client. */
 
     /* Used if there is the REDISMODULE_CTX_KEYS_POS_REQUEST flag set. */
     int *keys_pos;
@@ -203,6 +203,10 @@ typedef struct RedisModuleBlockedClient {
 static pthread_mutex_t moduleUnblockedClientsMutex = PTHREAD_MUTEX_INITIALIZER;
 static list *moduleUnblockedClients;
 
+/* We need a mutex that is unlocked / relocked in beforeSleep() in order to
+ * allow thread safe contexts to execute commands at a safe moment. */
+static pthread_mutex_t moduleGIL = PTHREAD_MUTEX_INITIALIZER;
+
 /* --------------------------------------------------------------------------
  * Prototypes
  * -------------------------------------------------------------------------- */
@@ -3278,6 +3282,24 @@ void *RM_GetBlockedClientPrivateData(RedisModuleCtx *ctx) {
     return ctx->blocked_privdata;
 }
 
+/* --------------------------------------------------------------------------
+ * Thread Safe Contexts
+ * -------------------------------------------------------------------------- */
+
+/* Operations executed in thread safe contexts use a global lock in order to
+ * be ran at a safe time. This function unlocks and re-acquire the locks:
+ * hopefully with *any* sane implementation of pthreads, this will allow the
+ * modules to make progresses.
+ *
+ * This function is called in beforeSleep(). */
+void moduleCooperativeMultiTaskingCycle(void) {
+    if (dictSize(modules) == 0) return; /* No modules, no async ops. */
+    pthread_mutex_unlock(&moduleGIL);
+    /* Here hopefully thread modules waiting to be executed at a safe time
+     * should be able to acquire the lock. */
+    pthread_mutex_lock(&moduleGIL);
+}
+
 /* --------------------------------------------------------------------------
  * Modules API internals
  * -------------------------------------------------------------------------- */
@@ -3329,6 +3351,10 @@ void moduleInitModulesSystem(void) {
      * and we do not want to block not in the read nor in the write half. */
     anetNonBlock(NULL,server.module_blocked_pipe[0]);
     anetNonBlock(NULL,server.module_blocked_pipe[1]);
+
+    /* Our thread-safe contexts GIL must start with already locked:
+     * it is just unlocked when it's safe. */
+    pthread_mutex_lock(&moduleGIL);
 }
 
 /* Load all the modules in the server.loadmodule_queue list, which is

src/server.c

@@ -1172,6 +1172,9 @@ int serverCron(struct aeEventLoop *eventLoop, long long id, void *clientData) {
 void beforeSleep(struct aeEventLoop *eventLoop) {
     UNUSED(eventLoop);
 
+    /* Give some run time to modules threads using thread safe contexts. */
+    moduleCooperativeMultiTaskingCycle();
+
     /* Call the Redis Cluster before sleep function. Note that this function
      * may change the state of Redis Cluster (from ok to fail or vice versa),
      * so it's a good idea to call it before serving the unblocked clients

src/server.h

@@ -1294,6 +1294,7 @@ void unblockClientFromModule(client *c);
 void moduleHandleBlockedClients(void);
 void moduleBlockedClientTimedOut(client *c);
 void moduleBlockedClientPipeReadable(aeEventLoop *el, int fd, void *privdata, int mask);
+void moduleCooperativeMultiTaskingCycle(void);
 
 /* Utils */
 long long ustime(void);