Fix module LatencyAddSample still work when latency-monitor-threshold is 0 (#1541)

When latency-monitor-threshold is set to 0, it means the latency monitor
is disabled, and in VM_LatencyAddSample, we wrote the condition
incorrectly, causing us to record latency when latency was turned off.

This bug was introduced in the very first day, see e3b1d6d, it was merged
in 2019.

Signed-off-by: Binbin <binloveplay1314@qq.com>

src/module.c

@@ -7680,7 +7680,7 @@ void VM__Assert(const char *estr, const char *file, int line) {
  * command. The call is skipped if the latency is smaller than the configured
  * latency-monitor-threshold. */
 void VM_LatencyAddSample(const char *event, mstime_t latency) {
-    if (latency >= server.latency_monitor_threshold) latencyAddSample(event, latency);
+    latencyAddSampleIfNeeded(event, latency);
 }
 
 /* --------------------------------------------------------------------------

tests/modules/basics.c

@@ -669,6 +669,24 @@ err:
     return ValkeyModule_ReplyWithSimpleString(ctx, "ERR");
 }
 
+/* test.latency latency_ms */
+int TestLatency(ValkeyModuleCtx *ctx, ValkeyModuleString **argv, int argc) {
+    if (argc != 2) {
+        ValkeyModule_WrongArity(ctx);
+        return VALKEYMODULE_OK;
+    }
+
+    long long latency_ms;
+    if (ValkeyModule_StringToLongLong(argv[1], &latency_ms) != VALKEYMODULE_OK) {
+        ValkeyModule_ReplyWithError(ctx, "Invalid integer value");
+        return VALKEYMODULE_OK;
+    }
+
+    ValkeyModule_LatencyAddSample("test", latency_ms);
+    ValkeyModule_ReplyWithSimpleString(ctx, "OK");
+    return VALKEYMODULE_OK;
+}
+
 /* TEST.CTXFLAGS -- Test GetContextFlags. */
 int TestCtxFlags(ValkeyModuleCtx *ctx, ValkeyModuleString **argv, int argc) {
     VALKEYMODULE_NOT_USED(argc);
@@ -1048,5 +1066,8 @@ int ValkeyModule_OnLoad(ValkeyModuleCtx *ctx, ValkeyModuleString **argv, int arg
         TestNotifications,"write deny-oom",1,1,1) == VALKEYMODULE_ERR)
         return VALKEYMODULE_ERR;
 
+    if (ValkeyModule_CreateCommand(ctx, "test.latency", TestLatency, "readonly", 0, 0, 0) == VALKEYMODULE_ERR)
+        return VALKEYMODULE_ERR;
+
     return VALKEYMODULE_OK;
 }

tests/unit/moduleapi/basics.tcl

@@ -39,6 +39,23 @@ start_server {tags {"modules"}} {
         verify_log_message 0 "*Module name is busy*" 0
     }
 
+    test "test latency" {
+        r config set latency-monitor-threshold 0
+        r latency reset
+        r test.latency 0
+        r test.latency 1
+        assert_equal {} [r latency latest]
+        assert_equal {} [r latency history test]
+
+        r config set latency-monitor-threshold 1
+        r test.latency 0
+        assert_equal 0 [llength [r latency history test]]
+        r test.latency 1
+        assert_match {*test * 1 1*} [r latency latest]
+        r test.latency 2
+        assert_match {*test * 2 2*} [r latency latest]
+    }
+
     test "Unload the module - basics" {
         assert_equal {OK} [r module unload test]
     }