RM_ThreadSafeContextTryLock a non-blocking method for acquiring GIL (#7738)

Co-authored-by: Yossi Gottlieb <yossigo@gmail.com>
Co-authored-by: Oran Agra <oran@redislabs.com>
(cherry picked from commit 042189fd87)

tests/modules/Makefile

@@ -23,7 +23,9 @@ TEST_MODULES = \
     scan.so \
     datatype.so \
     auth.so \
-    keyspace_events.so
+    keyspace_events.so \
+    blockedclient.so
+
 
 .PHONY: all
 

tests/modules/blockedclient.c

@@ -0,0 +1,82 @@
+#define REDISMODULE_EXPERIMENTAL_API
+#include "redismodule.h"
+#include <assert.h>
+#include <stdio.h>
+#include <pthread.h>
+
+#define UNUSED(V) ((void) V)
+
+void *sub_worker(void *arg) {
+    // Get Redis module context
+    RedisModuleCtx *ctx = (RedisModuleCtx *)arg;
+
+    // Try acquiring GIL
+    int res = RedisModule_ThreadSafeContextTryLock(ctx);
+
+    // GIL is already taken by the calling thread expecting to fail.
+    assert(res != REDISMODULE_OK);
+
+    return NULL;
+}
+
+void *worker(void *arg) {
+    // Retrieve blocked client
+    RedisModuleBlockedClient *bc = (RedisModuleBlockedClient *)arg;
+
+    // Get Redis module context
+    RedisModuleCtx *ctx = RedisModule_GetThreadSafeContext(bc);
+
+    // Acquire GIL
+    RedisModule_ThreadSafeContextLock(ctx);
+
+    // Create another thread which will try to acquire the GIL
+    pthread_t tid;
+    int res = pthread_create(&tid, NULL, sub_worker, ctx);
+    assert(res == 0);
+
+    // Wait for thread
+    pthread_join(tid, NULL);
+
+    // Release GIL
+    RedisModule_ThreadSafeContextUnlock(ctx);
+
+    // Reply to client
+    RedisModule_ReplyWithSimpleString(ctx, "OK");
+
+    // Unblock client
+    RedisModule_UnblockClient(bc, NULL);
+
+    return NULL;
+}
+
+int acquire_gil(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
+{
+    UNUSED(argv);
+    UNUSED(argc);
+
+    /* This command handler tries to acquire the GIL twice
+     * once in the worker thread using "RedisModule_ThreadSafeContextLock"
+     * second in the sub-worker thread
+     * using "RedisModule_ThreadSafeContextTryLock"
+     * as the GIL is already locked. */
+    RedisModuleBlockedClient *bc = RedisModule_BlockClient(ctx, NULL, NULL, NULL, 0);
+
+    pthread_t tid;
+    int res = pthread_create(&tid, NULL, worker, bc);
+    assert(res == 0);
+
+    return REDISMODULE_OK;
+}
+
+int RedisModule_OnLoad(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    REDISMODULE_NOT_USED(argv);
+    REDISMODULE_NOT_USED(argc);
+
+    if (RedisModule_Init(ctx, "blockedclient", 1, REDISMODULE_APIVER_1)== REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+
+    if (RedisModule_CreateCommand(ctx, "acquire_gil", acquire_gil, "", 0, 0, 0) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+
+    return REDISMODULE_OK;
+}

tests/unit/moduleapi/blockedclient.tcl

@@ -0,0 +1,11 @@
+# source tests/support/util.tcl
+
+set testmodule [file normalize tests/modules/blockedclient.so]
+
+start_server {tags {"modules"}} {
+    r module load $testmodule
+
+    test {Locked GIL acquisition} {
+        assert_match "OK" [r acquire_gil]
+    }
+}