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package shm
// #cgo LDFLAGS: -lrt -lpthread
// #include "shm_lock.h"
// const uint32_t bitmap_size_c = BITMAP_SIZE;
import "C"
import (
"syscall"
"github.com/pkg/errors"
)
var (
bitmapSize uint32 = uint32(C.bitmap_size_c)
)
// SHMLocks is a struct enabling POSIX semaphore locking in a shared memory
// segment
type SHMLocks struct {
lockStruct *C.shm_struct_t
valid bool
maxLocks uint32
}
// 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 be a multiple of the lock bitmap size (by default, 32).
func CreateSHMLock(numLocks uint32) (*SHMLocks, error) {
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
lockStruct := C.setup_lock_shm(C.uint32_t(numLocks), &errCode)
if lockStruct == nil {
// We got a null pointer, so something errored
return nil, syscall.Errno(-1 * errCode)
}
locks.lockStruct = lockStruct
locks.maxLocks = numLocks
locks.valid = true
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 and be a multiple of the lock bitmap size (default
// 32).
func OpenSHMLock(numLocks uint32) (*SHMLocks, error) {
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
lockStruct := C.open_lock_shm(C.uint32_t(numLocks), &errCode)
if lockStruct == nil {
// We got a null pointer, so something errored
return nil, syscall.Errno(-1 * errCode)
}
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")
}
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)
}
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)
}
return nil
}
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