---
description: "Learn more about: Warning C26110"
title: Warning C26110
ms.date: 10/01/2019
f1_keywords: ["C26110"]
helpviewer_keywords: ["C26110"]
ms.assetid: d82b79ec-6d7f-438b-bd6a-da874a3e08e5
---
# Warning C26110

> Caller failing to hold lock '*lock*' before calling function '*func*'.

When a lock is required, make sure to clarify whether the function itself, or its caller, should acquire the lock. Warning C26110 is issued when there's a violation of the `_Requires_lock_held_` annotation, or other lock-related annotations. For more information, see [Annotating Locking Behavior](annotating-locking-behavior.md)

## Example

In the following example, warning C26110 is generated because the annotation `_Requires_lock_held_` on function `LockRequired` states that the caller of `LockRequired` must acquire the lock before it calls `LockRequired`. Without this annotation, `LockRequired` has to acquire the lock before it accesses any shared data protected by the lock.

```cpp
typedef struct _DATA
{
    CRITICAL_SECTION cs;
    int d;
} DATA;

_Requires_lock_held_(p->cs)

void LockRequired(DATA* p)
{
    p->d = 0;
}

void LockNotHeld(DATA* p)
{
    LockRequired(p); // Warning C26110
}
```