Asserting Lock State

assert(MUTEX_HELD(lock_expr) && ...);

This assertion is widely used within the kernel. It performs runtime checking if assertions are enabled. The same capability exists in user code.

This code does roughly the same thing during LockLint analysis as it does when the code is actually run with assertions enabled; that is, it reports an error if the executing thread does not hold the lock as described.

The thread library performs a weaker test, only checking that some thread holds the lock. LockLint performs the stronger test.

LockLint recognizes the use of MUTEX_HELD(), RW_READ_HELD(), RW_WRITE_HELD(), and RW_LOCK_HELD() macros, and negations thereof. Such macro calls may be combined using the && operators. For example, the following assertion causes LockLint to check that a mutex is not held and that a readers-writer lock is write-held:

assert(p && !MUTEX_HELD(&p->mtx) && RW_WRITE_HELD(&p->rwlock));

LockLint also recognizes expressions like:

MUTEX_HELD(&foo) == 0