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-# CheckLocks Analyzer
-
-<!--* freshness: { owner: 'gvisor-eng' reviewed: '2021-10-20' } *-->
-
-Checklocks is an analyzer for lock and atomic constraints. The analyzer relies
-on explicit annotations to identify fields that should be checked for access.
-
-## Atomic annotations
-
-Individual struct members may be noted as requiring atomic access. These
-annotations are of the form:
-
-```go
-type foo struct {
- // +checkatomic
- bar int32
-}
-```
-
-This will ensure that all accesses to bar are atomic, with the exception of
-operations on newly allocated objects.
-
-## Lock annotations
-
-Individual struct members may be protected by annotations that indicate locking
-requirements for accessing members. These annotations are of the form:
-
-```go
-type foo struct {
- mu sync.Mutex
- // +checklocks:mu
- bar int
-
- foo int // No annotation on foo means it's not guarded by mu.
-
- secondMu sync.Mutex
-
- // Multiple annotations indicate that both must be held but the
- // checker does not assert any lock ordering.
- // +checklocks:secondMu
- // +checklocks:mu
- foobar int
-}
-```
-
-The checklocks annotation may also apply to functions. For example:
-
-```go
-// +checklocks:f.mu
-func (f *foo) doThingLocked() { }
-```
-
-This will check that the "f.mu" is locked for any calls, where possible.
-
-In case of functions which initialize structs that may have annotations one can
-use the following annotation on the function to disable reporting by the lock
-checker. The lock checker will still track any mutexes acquired or released but
-won't report any failures for this function for unguarded field access.
-
-```go
-// +checklocks:ignore
-func newXXX() *X {
-...
-}
-```
-
-***The checker treats both 'sync.Mutex' and 'sync.RWMutex' identically, i.e, as
-a sync.Mutex. The checker does not distinguish between read locks vs. exclusive
-locks and treats all locks as exclusive locks***.
-
-For cases the checker is able to correctly handle today please see test/test.go.
-
-The checklocks check also flags any invalid annotations where the mutex
-annotation refers either to something that is not a 'sync.Mutex' or
-'sync.RWMutex' or where the field does not exist at all. This will prevent the
-annotations from becoming stale over time as fields are renamed, etc.
-
-## Lock suggestions
-
-Based on locks held during field access, the analyzer will suggest annotations.
-These can be ignored with the standard `+checklocksignore` annotation.
-
-The annotation will be generated when the lock is held the vast majority of the
-time the field is accessed. Note that it is possible for this frequency to be
-greater than 100%, if the lock is held multiple times. For example:
-
-```go
-func foo(ts1 *testStruct, ts2 *testStruct) {
- ts1.Lock()
- ts2.Lock()
- ts1.gaurdedField = 1 // 200% locks held.
- ts1.Unlock()
- ts2.Unlock()
-}
-```
-
-## Currently not supported
-
-1. Anonymous functions are not correctly evaluated. The analyzer does not
- currently support specifying annotations on anonymous functions as a result
- evaluation of a function that accesses protected fields will fail.
-
-```go
-type A struct {
- mu sync.Mutex
-
- // +checklocks:mu
- x int
-}
-
-func abc() {
- var a A
- f := func() { a.x = 1 } <=== This line will be flagged by analyzer
- a.mu.Lock()
- f()
- a.mu.Unlock()
-}
-```
-
-### Explicitly Not Supported
-
-1. The checker will not support guards on anything other than the cases
- described above. For example, global mutexes cannot be referred to by
- checklocks. Only struct members can be used.
-
-2. The checker will not support checking for lock ordering violations.
-
-## Mixed mode
-
-Some members may allow read-only atomic access, but be protected against writes
-by a mutex. Generally, this imposes the following requirements:
-
-For a read, one of the following must be true:
-
-1. A lock held be held.
-1. The access is atomic.
-
-For a write, both of the following must be true:
-
-1. The lock must be held.
-1. The write must be atomic.
-
-In order to annotate a relevant field, simply apply *both* annotations from
-above. For example:
-
-```go
-type foo struct {
- mu sync.Mutex
- // +checklocks:mu
- // +checkatomic
- bar int32
-}
-```