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heed: use read-txn-no-tls for Send read transactions

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hinto.janai 2024-04-23 18:56:52 -04:00
parent ba1d96522f
commit 6a0a17aead
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3 changed files with 23 additions and 7 deletions
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1
Cargo.lock generated
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@ -623,6 +623,7 @@ dependencies = [
"serde",
"tempfile",
"thiserror",
"thread_local",
"tokio",
"tokio-util",
"tower",

18
database/Cargo.toml
View file

@ -35,15 +35,19 @@ page_size = { version = "0.6.0" } # Needed for database resizes, they mus
thiserror = { workspace = true }
# `service` feature.
crossbeam = { workspace = true, features = ["std"], optional = true }
futures = { workspace = true, optional = true }
tokio = { workspace = true, features = ["full"], optional = true }
tokio-util = { workspace = true, features = ["full"], optional = true }
tower = { workspace = true, features = ["full"], optional = true }
rayon = { workspace = true, optional = true }
crossbeam = { workspace = true, features = ["std"], optional = true }
futures = { workspace = true, optional = true }
tokio = { workspace = true, features = ["full"], optional = true }
tokio-util = { workspace = true, features = ["full"], optional = true }
tower = { workspace = true, features = ["full"], optional = true }
thread_local = { workspace = true }
rayon = { workspace = true, optional = true }
# Optional features.
heed = { version = "0.20.0-alpha.9", optional = true }
# SAFETY: Do not remove the `read-txn-no-tls` feature.
# Required for `heed`'s read transaction to be `Send`.
# See <TODO: link_to_safety_commit_line> for more info.
heed = { version = "0.20.0-alpha.9", features = ["read-txn-no-tls"], optional = true }
redb = { version = "2.0.0", optional = true }
serde = { workspace = true, optional = true }

11
database/src/backend/heed/database.rs
View file

@ -49,6 +49,17 @@ pub(super) struct HeedTableRw<'env, 'tx, T: Table> {
pub(super) tx_rw: &'tx RefCell<heed::RwTxn<'env>>,
}
/// SAFETY: `cuprate_database`'s Cargo.toml enables a feature
/// for `heed` that turns on the `MDB_NOTLS` flag for LMDB.
///
/// This makes read transactions `Send`, but only if that flag is enabled.
///
/// This is required as in `crate::service` we must put our transactions and
/// tables inside `ThreadLocal`'s to use across multiple threads.
///
/// `ThreadLocal<T>` requires that `T: Send`.
unsafe impl<T: Table> Send for HeedTableRo<'_, T> {}
//---------------------------------------------------------------------------------------------------- Shared functions
// FIXME: we cannot just deref `HeedTableRw -> HeedTableRo` and
// call the functions since the database is held by value, so