package shm // #cgo LDFLAGS: -lrt -lpthread // #include // #include "shm_lock.h" // const uint32_t bitmap_size_c = BITMAP_SIZE; import "C" import ( "runtime" "syscall" "unsafe" "github.com/pkg/errors" "github.com/sirupsen/logrus" ) var ( // BitmapSize is the size of the bitmap used when managing SHM locks. // an SHM lock manager's max locks will be rounded up to a multiple of // this number. BitmapSize uint32 = uint32(C.bitmap_size_c) ) // SHMLocks is a struct enabling POSIX semaphore locking in a shared memory // segment. type SHMLocks struct { // nolint lockStruct *C.shm_struct_t maxLocks uint32 valid bool } // CreateSHMLock sets up a shared-memory segment holding a given number of POSIX // semaphores, and returns a struct that can be used to operate on those locks. // numLocks must not be 0, and may be rounded up to a multiple of the bitmap // size used by the underlying implementation. func CreateSHMLock(path string, numLocks uint32) (*SHMLocks, error) { if numLocks == 0 { return nil, errors.Wrapf(syscall.EINVAL, "number of locks must be greater than 0") } locks := new(SHMLocks) cPath := C.CString(path) defer C.free(unsafe.Pointer(cPath)) var errCode C.int lockStruct := C.setup_lock_shm(cPath, C.uint32_t(numLocks), &errCode) if lockStruct == nil { // We got a null pointer, so something errored return nil, errors.Wrapf(syscall.Errno(-1*errCode), "failed to create %d locks in %s", numLocks, path) } locks.lockStruct = lockStruct locks.maxLocks = uint32(lockStruct.num_locks) locks.valid = true logrus.Debugf("Initialized SHM lock manager at path %s", path) return locks, nil } // OpenSHMLock opens an existing shared-memory segment holding a given number of // POSIX semaphores. numLocks must match the number of locks the shared memory // segment was created with. func OpenSHMLock(path string, numLocks uint32) (*SHMLocks, error) { if numLocks == 0 { return nil, errors.Wrapf(syscall.EINVAL, "number of locks must be greater than 0") } locks := new(SHMLocks) cPath := C.CString(path) defer C.free(unsafe.Pointer(cPath)) var errCode C.int lockStruct := C.open_lock_shm(cPath, C.uint32_t(numLocks), &errCode) if lockStruct == nil { // We got a null pointer, so something errored return nil, errors.Wrapf(syscall.Errno(-1*errCode), "failed to open %d locks in %s", numLocks, path) } locks.lockStruct = lockStruct locks.maxLocks = numLocks locks.valid = true return locks, nil } // GetMaxLocks returns the maximum number of locks in the SHM func (locks *SHMLocks) GetMaxLocks() uint32 { return locks.maxLocks } // Close closes an existing shared-memory segment. // The segment will be rendered unusable after closing. // WARNING: If you Close() while there are still locks locked, these locks may // fail to release, causing a program freeze. // Close() is only intended to be used while testing the locks. func (locks *SHMLocks) Close() error { if !locks.valid { return errors.Wrapf(syscall.EINVAL, "locks have already been closed") } locks.valid = false retCode := C.close_lock_shm(locks.lockStruct) if retCode < 0 { // Negative errno returned return syscall.Errno(-1 * retCode) } return nil } // AllocateSemaphore allocates a semaphore from a shared-memory segment for use // by a container or pod. // Returns the index of the semaphore that was allocated. // Allocations past the maximum number of locks given when the SHM segment was // created will result in an error, and no semaphore will be allocated. func (locks *SHMLocks) AllocateSemaphore() (uint32, error) { if !locks.valid { return 0, errors.Wrapf(syscall.EINVAL, "locks have already been closed") } // This returns a U64, so we have the full u32 range available for // semaphore indexes, and can still return error codes. retCode := C.allocate_semaphore(locks.lockStruct) if retCode < 0 { // Negative errno returned return 0, syscall.Errno(-1 * retCode) } return uint32(retCode), nil } // DeallocateSemaphore frees a semaphore in a shared-memory segment so it can be // reallocated to another container or pod. // The given semaphore must be already allocated, or an error will be returned. func (locks *SHMLocks) DeallocateSemaphore(sem uint32) error { if !locks.valid { return errors.Wrapf(syscall.EINVAL, "locks have already been closed") } if sem > locks.maxLocks { return errors.Wrapf(syscall.EINVAL, "given semaphore %d is higher than maximum locks count %d", sem, locks.maxLocks) } retCode := C.deallocate_semaphore(locks.lockStruct, C.uint32_t(sem)) if retCode < 0 { // Negative errno returned return syscall.Errno(-1 * retCode) } return nil } // LockSemaphore locks the given semaphore. // If the semaphore is already locked, LockSemaphore will block until the lock // can be acquired. // There is no requirement that the given semaphore be allocated. // This ensures that attempts to lock a container after it has been deleted, // but before the caller has queried the database to determine this, will // succeed. func (locks *SHMLocks) LockSemaphore(sem uint32) error { if !locks.valid { return errors.Wrapf(syscall.EINVAL, "locks have already been closed") } if sem > locks.maxLocks { return errors.Wrapf(syscall.EINVAL, "given semaphore %d is higher than maximum locks count %d", sem, locks.maxLocks) } // For pthread mutexes, we have to guarantee lock and unlock happen in // the same thread. runtime.LockOSThread() retCode := C.lock_semaphore(locks.lockStruct, C.uint32_t(sem)) if retCode < 0 { // Negative errno returned return syscall.Errno(-1 * retCode) } return nil } // UnlockSemaphore unlocks the given semaphore. // Unlocking a semaphore that is already unlocked with return EBUSY. // There is no requirement that the given semaphore be allocated. // This ensures that attempts to lock a container after it has been deleted, // but before the caller has queried the database to determine this, will // succeed. func (locks *SHMLocks) UnlockSemaphore(sem uint32) error { if !locks.valid { return errors.Wrapf(syscall.EINVAL, "locks have already been closed") } if sem > locks.maxLocks { return errors.Wrapf(syscall.EINVAL, "given semaphore %d is higher than maximum locks count %d", sem, locks.maxLocks) } retCode := C.unlock_semaphore(locks.lockStruct, C.uint32_t(sem)) if retCode < 0 { // Negative errno returned return syscall.Errno(-1 * retCode) } // For pthread mutexes, we have to guarantee lock and unlock happen in // the same thread. // OK if we take multiple locks - UnlockOSThread() won't actually unlock // until the number of calls equals the number of calls to // LockOSThread() runtime.UnlockOSThread() return nil }