use std::path::PathBuf; use git_features::threading::OwnShared; use crate::store_impl::{file, packed}; impl file::Store {    /// Return a packed transaction ready to receive updates. Use this to create or update `packed-refs`.    /// Note that if you already have a [`packed::Buffer`] then use its [`packed::Buffer::into_transaction()`] method instead.    pub(crate) fn packed_transaction(        &self,        lock_mode: git_lock::acquire::Fail,    ) -> Result<packed::Transaction, transaction::Error> {        let lock = git_lock::File::acquire_to_update_resource(self.packed_refs_path(), lock_mode, None)?;        // We 'steal' the possibly existing packed buffer which may safe time if it's already there and fresh.        // If nothing else is happening, nobody will get to see the soon stale buffer either, but if so, they will pay        // for reloading it. That seems preferred over always loading up a new one.        Ok(packed::Transaction::new_from_pack_and_lock(            self.assure_packed_refs_uptodate()?,            lock,        ))    }     /// Try to open a new packed buffer. It's not an error if it doesn't exist, but yields `Ok(None)`.    pub fn open_packed_buffer(&self) -> Result<Option<packed::Buffer>, packed::buffer::open::Error> {        let need_more_than_this_many_bytes_to_use_mmap = 32 * 1024;        match packed::Buffer::open(self.packed_refs_path(), need_more_than_this_many_bytes_to_use_mmap) {            Ok(buf) => Ok(Some(buf)),            Err(packed::buffer::open::Error::Io(err)) if err.kind() == std::io::ErrorKind::NotFound => Ok(None),            Err(err) => Err(err),        }    }     /// Return a possibly cached packed buffer with shared ownership. At retrieval it will assure it's up to date, but    /// after that it can be considered a snapshot as it cannot change anymore.    ///    /// Use this to make successive calls to [`file::Store::try_find_packed()`]    /// or obtain iterators using [`file::Store::iter_packed()`] in a way that assures the packed-refs content won't change.    pub fn cached_packed_buffer(&self) -> Result<Option<OwnShared<packed::Buffer>>, packed::buffer::open::Error> {        self.assure_packed_refs_uptodate()    }     /// Return the path at which packed-refs would usually be stored    pub fn packed_refs_path(&self) -> PathBuf {        self.base.join("packed-refs")    }} ///pub mod transaction {    use quick_error::quick_error;     use crate::store_impl::packed;     quick_error! {        /// The error returned by [`file::Store::packed_transaction`][crate::file::Store::packed_transaction()].        #[derive(Debug)]        #[allow(missing_docs)]        pub enum Error {            BufferOpen(err: packed::buffer::open::Error) {                display("An existing pack couldn't be opened or read when preparing a transaction")                source(err)                from()            }            TransactionLock(err: git_lock::acquire::Error) {                display("The lock for a packed transaction could not be obtained")                source(err)                from()            }        }    }} pub(crate) mod modifiable {    use std::time::SystemTime;     use git_features::threading::{get_mut, get_ref, OwnShared};     use crate::{file, packed};     #[derive(Debug, Default)]    pub(crate) struct State {        buffer: Option<OwnShared<packed::Buffer>>,        modified: Option<SystemTime>,    }     impl file::Store {        /// Always reload the internally cached packed buffer from disk. This can be necessary if the caller knows something changed        /// but fears the change is not picked up due to lack of precision in fstat mtime calls.        pub(crate) fn force_refresh_packed_buffer(&self) -> Result<(), packed::buffer::open::Error> {            let mut state = get_mut(&self.packed);            state.buffer = self.open_packed_buffer()?.map(OwnShared::new);            Ok(())        }        pub(crate) fn assure_packed_refs_uptodate(            &self,        ) -> Result<Option<OwnShared<packed::Buffer>>, packed::buffer::open::Error> {            let packed_refs_path = self.packed_refs_path();            let packed_refs_modified_time = || packed_refs_path.metadata().and_then(|m| m.modified()).ok();            let state = get_ref(&self.packed);            let recent_modification = packed_refs_modified_time();            let buffer = match (&state.modified, recent_modification) {                (None, None) => state.buffer.clone(),                (Some(_), None) => {                    drop(state);                    let mut state = get_mut(&self.packed);                    // Still in the same situation? If so, drop the loaded buffer                    if let (Some(_), None) = (state.modified, packed_refs_modified_time()) {                        state.buffer = None;                        state.modified = None;                    }                    state.buffer.clone()                }                (Some(cached_time), Some(modified_time)) => {                    if *cached_time < modified_time {                        drop(state);                        let mut state = get_mut(&self.packed);                        // in the common case, we check again and do what we do only if we are                        // still in the same situation, writers pile up.                        match (state.modified, packed_refs_modified_time()) {                            (Some(cached_time), Some(modified_time)) if cached_time < modified_time => {                                state.buffer = self.open_packed_buffer()?.map(OwnShared::new);                                state.modified = Some(modified_time);                            }                            _ => {}                        }                        state.buffer.clone()                    } else {                        // Note that this relies on sub-section precision or else is a race when the packed file was just changed.                        // It's nothing we can know though, so… up to the caller unfortunately.                        state.buffer.clone()                    }                }                (None, Some(_modified_time)) => {                    drop(state);                    let mut state = get_mut(&self.packed);                    // Still in the same situation? If so, load the buffer.                    if let (None, Some(modified_time)) = (state.modified, packed_refs_modified_time()) {                        state.buffer = self.open_packed_buffer()?.map(OwnShared::new);                        state.modified = Some(modified_time);                    }                    state.buffer.clone()                }            };            Ok(buffer)        }    }}