Enum DbPool 

pub enum DbPool {
    PerThread {
        path: PathBuf,
        poll: Box<ReentrantMutex<Db<ReadOnly>>>,
        conns: Mutex<HashMap<ThreadId, Arc<ReentrantMutex<Db<ReadOnly>>>>>,
    },
    Shared(Arc<ReentrantMutex<Db<ReadOnly>>>),
}

with and with_poll may nest freely, on any variant: PerThread reads hand out cloned Arcs from the pool-owned map, and the connection locks are reentrant.

The poll/conns asymmetry is deliberate. poll is uniquely owned (the Box only keeps the variant small) because with_poll locks it in place and takes no other lock. conns values are Arc-wrapped so with can clone a handle and release the map guard before running the caller’s closure — holding the (non-reentrant) map guard across it would deadlock nested with. The inner ReentrantMutex is never contended (only its owning thread locks it) but is load-bearing for the type system: Db is Send + !Sync, so the mutex wrapper is what keeps the map field, and therefore DbPool, Send + Sync.

Variants

PerThread

Fields

path: PathBuf

poll: Box<ReentrantMutex<Db<ReadOnly>>>

conns: Mutex<HashMap<ThreadId, Arc<ReentrantMutex<Db<ReadOnly>>>>>

Shared(Arc<ReentrantMutex<Db<ReadOnly>>>)

Implementations

impl DbPool

pub fn new(db: Db) -> Result<DbPool>

Build a pool from the DB used to construct the mount. File-backed DBs become per-thread pools (the passed connection becomes the poll connection — workers open their own); in-memory DBs are wrapped in a shared mutex.

pub fn with_poll<R>( &self, f: impl FnOnce(&Db<ReadOnly>) -> Result<R>, ) -> Result<R>

Run f with the persistent poll connection.

For PerThread pools, PRAGMA data_version is connection-relative: a fresh thread-local connection starts at 0, so it can’t detect changes that happened before it opened. The poll connection is the original writer Db, kept alive precisely so it can observe incremental changes from other connections. For Shared pools (in-memory), the single shared connection serves both roles.

pub fn with<R>(&self, f: impl FnOnce(&Db<ReadOnly>) -> Result<R>) -> Result<R>

Run f with a read connection.