feat(ffi) produce an error on 'shm:set()' when already locked

Catch the case and produce an error instead of entering a deadlock.

lib/resty/wasmx/shm.lua

@@ -346,6 +346,10 @@ local function shm_kv_set(zone, key, value, cas)
         return nil, "no memory"
     end
 
+    if rc == FFI_ABORT then
+        return nil, "locked"
+    end
+
     assert_debug(rc == FFI_OK)
 
     return tonumber(written[0])

src/common/lua/ngx_wasm_lua_ffi.c

@@ -397,6 +397,11 @@ ngx_wa_ffi_shm_kv_set(ngx_wa_shm_t *shm, ngx_str_t *k, ngx_str_t *v,
 
     ngx_wa_assert(shm->type == NGX_WA_SHM_TYPE_KV);
 
+    if (ngx_wa_shm_locked(shm)) {
+        /* already locked by the current worker */
+        return NGX_ABORT;
+    }
+
     ngx_wa_shm_lock(shm);
 
     rc = ngx_wa_shm_kv_set_locked(shm, k, v, cas, written);

t/04-openresty/ffi/shm/002-kv_set.t

@@ -105,8 +105,6 @@ cas must be a number
 
 
 === TEST 4: shm_kv - set() on locked shm
---- timeout: 1
---- abort
 --- shm_kv: kv 16k
 --- config
     location /t {
@@ -115,15 +113,17 @@ cas must be a number
 
             shm.kv:lock()
 
-            shm.kv:set("kv/k1", "v1")
+            local written, err = shm.kv:set("kv/k1", "v1")
 
             shm.kv:unlock()
 
-            ngx.say("fail")
+            assert(written == nil)
+
+            ngx.say(err)
         }
     }
---- error_code:
+--- response_body
+locked
 --- no_error_log
 [error]
 [crit]
-[emerg]