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d2b77f8b33
The original intent behind the requirement was to ensure that, if two SHM lock structs were open at the same time, we should not make such a runtime available to the user, and should clean it up instead. It turns out that we don't even need to open a second SHM lock struct - if we get an error mapping the first one due to a lock count mismatch, we can just delete it, and it cleans itself up when it errors. So there's no reason not to return a valid runtime. Signed-off-by: Matthew Heon <matthew.heon@pm.me>
110 lines
2.5 KiB
Go
110 lines
2.5 KiB
Go
// +build linux
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package lock
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import (
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"syscall"
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"github.com/containers/libpod/libpod/lock/shm"
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"github.com/pkg/errors"
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)
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// SHMLockManager manages shared memory locks.
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type SHMLockManager struct {
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locks *shm.SHMLocks
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}
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// NewSHMLockManager makes a new SHMLockManager with the given number of locks.
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// Due to the underlying implementation, the exact number of locks created may
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// be greater than the number given here.
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func NewSHMLockManager(path string, numLocks uint32) (Manager, error) {
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locks, err := shm.CreateSHMLock(path, numLocks)
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if err != nil {
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return nil, err
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}
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manager := new(SHMLockManager)
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manager.locks = locks
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return manager, nil
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}
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// OpenSHMLockManager opens an existing SHMLockManager with the given number of
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// locks.
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func OpenSHMLockManager(path string, numLocks uint32) (Manager, error) {
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locks, err := shm.OpenSHMLock(path, numLocks)
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if err != nil {
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return nil, err
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}
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manager := new(SHMLockManager)
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manager.locks = locks
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return manager, nil
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}
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// AllocateLock allocates a new lock from the manager.
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func (m *SHMLockManager) AllocateLock() (Locker, error) {
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semIndex, err := m.locks.AllocateSemaphore()
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if err != nil {
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return nil, err
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}
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lock := new(SHMLock)
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lock.lockID = semIndex
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lock.manager = m
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return lock, nil
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}
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// RetrieveLock retrieves a lock from the manager given its ID.
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func (m *SHMLockManager) RetrieveLock(id uint32) (Locker, error) {
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lock := new(SHMLock)
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lock.lockID = id
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lock.manager = m
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if id >= m.locks.GetMaxLocks() {
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return nil, errors.Wrapf(syscall.EINVAL, "lock ID %d is too large - max lock size is %d",
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id, m.locks.GetMaxLocks()-1)
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}
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return lock, nil
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}
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// FreeAllLocks frees all locks in the manager.
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// This function is DANGEROUS. Please read the full comment in locks.go before
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// trying to use it.
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func (m *SHMLockManager) FreeAllLocks() error {
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return m.locks.DeallocateAllSemaphores()
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}
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// SHMLock is an individual shared memory lock.
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type SHMLock struct {
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lockID uint32
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manager *SHMLockManager
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}
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// ID returns the ID of the lock.
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func (l *SHMLock) ID() uint32 {
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return l.lockID
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}
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// Lock acquires the lock.
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func (l *SHMLock) Lock() {
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if err := l.manager.locks.LockSemaphore(l.lockID); err != nil {
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panic(err.Error())
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}
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}
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// Unlock releases the lock.
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func (l *SHMLock) Unlock() {
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if err := l.manager.locks.UnlockSemaphore(l.lockID); err != nil {
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panic(err.Error())
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}
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}
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// Free releases the lock, allowing it to be reused.
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func (l *SHMLock) Free() error {
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return l.manager.locks.DeallocateSemaphore(l.lockID)
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}
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