Clarify that Locker.Locked() checks if we have a write lock, since
that's what we care about whenever we check it.
Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>
Enable executing parallel `GetBlob()` executions in containers/image by
using reader-lock acquisitions in `ImageBigData()` and `Diff()`.
Signed-off-by: Valentin Rothberg <rothberg@redhat.com>
Implement reader-writer locks to allow allow multiple readers to hold
the lock in parallel.
* The locks are still based on fcntl(2).
* Changing the lock from a reader to a writer and vice versa will block
on the syscall.
* A writer lock can be held only by one process. To protect against
concurrent accesses by gourtines within the same process space, use a
writer mutex.
* Extend the Locker interface with the `RLock()` method to acquire a
reader lock. If the lock is set to be read-only, all calls to
`Lock()` will be redirected to `RLock()`. A reader lock is only
released via fcntl(2) when all gourtines within the same process space
have unlocked it. This is done via an internal counter which is
protected (among other things) by an internal state mutex.
* Panic on violations of the lock protocol, namely when calling
`Unlock()` on an unlocked lock. This helps detecting violations in
the code but also protects the storage from corruption. Doing this
has revealed some bugs fixed in ealier commits.
Signed-off-by: Valentin Rothberg <rothberg@redhat.com>
I have experienced "layer not known" corruption triggered by concurrent
buildah/skopeo processes, and hopefully lock sanity checks will help to
prevent this kind of problem.
Signed-off-by: Zac Medico <zmedico@gmail.com>
this stubs out for having platform-independent file locking
This still functions the same on `GOOS=linux`, and now succeeds for
`GOOS=windows`. But still fails on `freebsd`, `darwin`, `solaris`, etc
Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>
Use the standard library's "errors" package to create errors so that
backtraces in wrapped errors terminate at the point where the error was
first wrapped, and not at the line where we created the error, which
isn't as useful for troubleshooting.
Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>
We need to be able to acquire locks on storage areas which aren't
mounted read-write, which return errors when we attempt to open a file
in the mode where we can take write locks on them. This patch adds a
read-only lock type for use in those cases.
A given file can be opened for read-locking or write-locking, but not
both. Our Locker interface gains an IsReadWrite() method to let callers
tell the difference.
Based on patches by Dan Walsh <dwalsh@redhat.com>
Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>
Nalin Dahyabhai