Warning C26100

Race condition. Variable 'var' should be protected by lock 'lock'.

Remarks

The _Guarded_by_ annotation in the code specifies the lock to use to guard a shared variable. Warning C26100 is generated when the guard contract is violated.

Code analysis name: RACE_CONDITION

Examples

The following example generates warning C26100 because there's a violation of the _Guarded_by_ contract.

CRITICAL_SECTION gCS; _Guarded_by_(gCS) int gData; typedef struct _DATA { _Guarded_by_(cs) int data; CRITICAL_SECTION cs; } DATA; void Safe(DATA* p) { EnterCriticalSection(&p->cs); p->data = 1; // OK LeaveCriticalSection(&p->cs); EnterCriticalSection(&gCS); gData = 1; // OK LeaveCriticalSection(&gCS); } void Unsafe(DATA* p) { EnterCriticalSection(&p->cs); gData = 1; // Warning C26100 (wrong lock) LeaveCriticalSection(&p->cs); } 

The contract violation occurs because an incorrect lock is used in the function Unsafe. In this case, gCS is the correct lock to use.

Occasionally a shared variable only has to be guarded for write access but not for read access. In that case, use the _Write_guarded_by_ annotation, as shown in the following example.

CRITICAL_SECTION gCS; _Guarded_by_(gCS) int gData; typedef struct _DATA2 { _Write_guarded_by_(cs) int data; CRITICAL_SECTION cs; } DATA2; int Safe2(DATA2* p) { // OK: read does not have to be guarded int result = p->data; return result; } void Unsafe2(DATA2* p) { EnterCriticalSection(&gCS); // Warning C26100 (write has to be guarded by p->cs) p->data = 1; LeaveCriticalSection(&gCS); } 

This example also generates warning C26100 because it uses an incorrect lock in the function Unsafe2.