Add an SHM-backed Lock Manager implementation

Signed-off-by: Matthew Heon <matthew.heon@gmail.com>

libpod/lock/lock.go

@@ -1,7 +1,7 @@
 package lock
 
-// LockManager provides an interface for allocating multiprocess locks.
-// Locks returned by LockManager MUST be multiprocess - allocating a lock in
+// Manager provides an interface for allocating multiprocess locks.
+// Locks returned by Manager MUST be multiprocess - allocating a lock in
 // process A and retrieving that lock's ID in process B must return handles for
 // the same lock, and locking the lock in A should exclude B from the lock until
 // it is unlocked in A.
@@ -13,7 +13,7 @@ package lock
 // AllocateLock() must fail once all available locks have been allocated.
 // Locks are returned to use by calls to Free(), and can subsequently be
 // reallocated.
-type LockManager interface {
+type Manager interface {
 	// AllocateLock returns an unallocated lock.
 	// It is guaranteed that the same lock will not be returned again by
 	// AllocateLock until the returned lock has Free() called on it.
@@ -35,7 +35,7 @@ type LockManager interface {
 type Locker interface {
 	// ID retrieves the lock's ID.
 	// ID is guaranteed to uniquely identify the lock within the
-	// LockManager - that is, calling RetrieveLock with this ID will return
+	// Manager - that is, calling RetrieveLock with this ID will return
 	// another instance of the same lock.
 	ID() string
 	// Lock locks the lock.

libpod/lock/shm_lock.go

@@ -27,13 +27,13 @@ type SHMLocks struct {
 // semaphores, and returns a struct that can be used to operate on those locks.
 // numLocks must be a multiple of the lock bitmap size (by default, 32).
 func CreateSHMLock(numLocks uint32) (*SHMLocks, error) {
-	if numLocks % bitmapSize != 0 || numLocks == 0 {
+	if numLocks%bitmapSize != 0 || numLocks == 0 {
 		return nil, errors.Wrapf(syscall.EINVAL, "number of locks must be a multiple of %d", C.bitmap_size_c)
 	}
 
 	locks := new(SHMLocks)
 
-	var errCode C.int = 0
+	var errCode C.int
 	lockStruct := C.setup_lock_shm(C.uint32_t(numLocks), &errCode)
 	if lockStruct == nil {
 		// We got a null pointer, so something errored
@@ -52,13 +52,13 @@ func CreateSHMLock(numLocks uint32) (*SHMLocks, error) {
 // segment was created with and be a multiple of the lock bitmap size (default
 // 32).
 func OpenSHMLock(numLocks uint32) (*SHMLocks, error) {
-	if numLocks % bitmapSize != 0 || numLocks == 0 {
+	if numLocks%bitmapSize != 0 || numLocks == 0 {
 		return nil, errors.Wrapf(syscall.EINVAL, "number of locks must be a multiple of %d", C.bitmap_size_c)
 	}
 
 	locks := new(SHMLocks)
 
-	var errCode C.int = 0
+	var errCode C.int
 	lockStruct := C.open_lock_shm(C.uint32_t(numLocks), &errCode)
 	if lockStruct == nil {
 		// We got a null pointer, so something errored

libpod/lock/shm_lock_manager.go

@@ -0,0 +1,109 @@
+package lock
+
+import (
+	"fmt"
+	"math"
+	"strconv"
+	"syscall"
+
+	"github.com/pkg/errors"
+)
+
+// SHMLockManager manages shared memory locks.
+type SHMLockManager struct {
+	locks *SHMLocks
+}
+
+// NewSHMLockManager makes a new SHMLockManager with the given number of locks.
+func NewSHMLockManager(numLocks uint32) (Manager, error) {
+	locks, err := CreateSHMLock(numLocks)
+	if err != nil {
+		return nil, err
+	}
+
+	manager := new(SHMLockManager)
+	manager.locks = locks
+
+	return manager, nil
+}
+
+// OpenSHMLockManager opens an existing SHMLockManager with the given number of
+// locks.
+func OpenSHMLockManager(numLocks uint32) (LockManager, error) {
+	locks, err := OpenSHMLock(numLocks)
+	if err != nil {
+		return nil, err
+	}
+
+	manager := new(SHMLockManager)
+	manager.locks = locks
+
+	return manager, nil
+}
+
+// AllocateLock allocates a new lock from the manager.
+func (m *SHMLockManager) AllocateLock() (Locker, error) {
+	semIndex, err := m.locks.AllocateSemaphore()
+	if err != nil {
+		return nil, err
+	}
+
+	lock := new(SHMLock)
+	lock.lockID = semIndex
+	lock.manager = m
+
+	return lock, nil
+}
+
+// RetrieveLock retrieves a lock from the manager given its ID.
+func (m *SHMLockManager) RetrieveLock(id string) (Locker, error) {
+	intID, err := strconv.ParseInt(id, 16, 64)
+	if err != nil {
+		return errors.Wrapf(err, "given ID %q is not a valid SHMLockManager ID - cannot be parsed as int", id)
+	}
+
+	if intID < 0 {
+		return errors.Wrapf(syscall.EINVAL, "given ID %q is not a valid SHMLockManager ID - must be positive", id)
+	}
+
+	if intID > math.MaxUint32 {
+		return errors.Wrapf(syscall.EINVAL, "given ID %q is not a valid SHMLockManager ID - too large", id)
+	}
+
+	var u32ID uint32 = uint32(intID)
+	if u32ID >= m.locks.maxLocks {
+		return errors.Wrapf(syscall.EINVAL, "given ID %q is not a valid SHMLockManager ID - too large to fit", id)
+	}
+
+	lock := new(SHMLock)
+	lock.lockID = u32ID
+	lock.manager = m
+
+	return lock, nil
+}
+
+// SHMLock is an individual shared memory lock.
+type SHMLock struct {
+	lockID  uint32
+	manager *SHMLockManager
+}
+
+// ID returns the ID of the lock.
+func (l *SHMLock) ID() string {
+	return fmt.Sprintf("%x", l.lockID)
+}
+
+// Lock acquires the lock.
+func (l *SHMLock) Lock() error {
+	return l.manager.locks.LockSemaphore(l.lockID)
+}
+
+// Unlock releases the lock.
+func (l *SHMLock) Unlock() error {
+	return l.manager.locks.UnlockSemaphore(l.lockID)
+}
+
+// Free releases the lock, allowing it to be reused.
+func (l *SHMLock) Free() error {
+	return l.manager.locks.DeallocateSemaphore(l.lockID)
+}

libpod/lock/shm_lock_test.go

@@ -4,8 +4,8 @@ import (
 	"fmt"
 	"os"
 	"syscall"
-	"time"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -41,7 +41,6 @@ func TestMain(m *testing.M) {
 	os.Exit(exitCode)
 }
 
-
 func runLockTest(t *testing.T, testFunc func(*testing.T, *SHMLocks)) {
 	locks, err := OpenSHMLock(numLocks)
 	if err != nil {
@@ -66,7 +65,7 @@ func runLockTest(t *testing.T, testFunc func(*testing.T, *SHMLocks)) {
 		}
 	}()
 
-	success := t.Run("locks", func (t *testing.T) {
+	success := t.Run("locks", func(t *testing.T) {
 		testFunc(t, locks)
 	})
 	if !success {