How Data Is Protected

The following annotations are allowed both outside and inside a function definition. Remember that any name mentioned in an annotation must already have been declared.

NOTE(MUTEX_PROTECTS_DATA(Mutex, DataNameList))

NOTE(RWLOCK_PROTECTS_DATA(Rwlock, DataNameList))

NOTE(SCHEME_PROTECTS_DATA("description", DataNameList))

The first two annotations tell LockLint that the lock should be held whenever the specified data is accessed.

The third annotation, SCHEME_PROTECTS_DATA, describes how data are protected if it does not have a mutex or readers-writer lock. The description supplied for the scheme is simply text and is not semantically significant; LockLint responds by ignoring the specified data altogether. You may make description anything you like.

Some examples help show how these annotations are used. The first example is very simple, showing a lock that protects two variables:

mutex_t lock1;
int a,b;
NOTE(MUTEX_PROTECTS_DATA(lock1, a b))

In the next example, a number of different possibilities are shown. Some members of struct foo are protected by a static lock, while others are protected by the lock on foo. Another member of foo is protected by some convention regarding its use.

mutex_t lock1;
struct foo {
	mutex_t lock;
	int mbr1, mbr2;
	struct {
		int mbr1, mbr2;
		char* mbr3;
	} inner;
	int mbr4;
};
NOTE(MUTEX_PROTECTS_DATA(lock1, foo::{mbr1 inner.mbr1}))
NOTE(MUTEX_PROTECTS_DATA(foo::lock, foo::{mbr2 inner.mbr2}))
NOTE(SCHEME_PROTECTS_DATA("convention XYZ", inner.mbr3))

A datum can only be protected in one way. If multiple annotations about protection (not only these three but also READ_ONLY_DATA) are used for a single datum, later annotations silently override earlier annotations. This allows for easy description of a structure in which all but one or two members are protected in the same way. For example, most of the members of struct BAR below are protected by the lock on struct foo, but one is protected by a global lock.

mutex_t lock1;
typedef struct {
	int mbr1, mbr2, mbr3, mbr4;
} BAR;
NOTE(MUTEX_PROTECTS_DATA(foo::lock, BAR))
NOTE(MUTEX_PROTECTS_DATA(lock1, BAR::mbr3))