Fix encrypted heed3 parallel reads

heed3/Cargo.toml

@@ -26,9 +26,10 @@ synchronoise = "1.0.1"
 
 [dev-dependencies]
 argon2 = { version = "0.5.3", features = ["std"] }
+chacha20poly1305 = "0.10.1"
 memchr = "2.7.4"
+rayon = "1.10.0"
 serde = { version = "1.0.217", features = ["derive"] }
-chacha20poly1305 = "0.10.1"
 tempfile = "3.15.0"
 
 [target.'cfg(windows)'.dependencies]
@@ -116,5 +117,8 @@ name = "prev-snapshot"
 [[example]]
 name = "heed3-encrypted"
 
+[[example]]
+name = "heed3-encrypted-parallel-read"
+
 [[example]]
 name = "heed3-all-types"

heed3/examples/heed3-encrypted-parallel-read.rs

@@ -0,0 +1,61 @@
+use std::error::Error;
+
+use argon2::Argon2;
+use chacha20poly1305::{ChaCha20Poly1305, Key};
+use heed3::types::*;
+use heed3::EnvOpenOptions;
+
+fn main() -> Result<(), Box<dyn Error>> {
+    let env_path = tempfile::tempdir()?;
+    let password = "This is the password that will be hashed by the argon2 algorithm";
+    let salt = "The salt added to the password hashes to add more security when stored";
+
+    // We choose to use argon2 as our Key Derivation Function, but you can choose whatever you want.
+    // <https://github.com/RustCrypto/traits/tree/master/password-hash#supported-crates>
+    let mut key = Key::default();
+    Argon2::default().hash_password_into(password.as_bytes(), salt.as_bytes(), &mut key)?;
+
+    // We open the environment
+    let mut options = EnvOpenOptions::new();
+    let env = unsafe {
+        options
+            .map_size(10 * 1024 * 1024) // 10MB
+            .max_dbs(3)
+            .open_encrypted::<ChaCha20Poly1305, _>(key, &env_path)?
+    };
+
+    let key1 = "first-key";
+    let val1 = "this is a secret info";
+    let key2 = "second-key";
+    let val2 = "this is another secret info";
+
+    // We create database and write secret values in it
+    let mut wtxn = env.write_txn()?;
+    let db = env.create_database::<Str, Str>(&mut wtxn, Some("first"))?;
+    db.put(&mut wtxn, key1, val1)?;
+    db.put(&mut wtxn, key2, val2)?;
+    wtxn.commit()?;
+
+    let pool = rayon::ThreadPoolBuilder::new().num_threads(12).build().unwrap();
+
+    let results = pool.broadcast(|_| {
+        let mut rtxn = env.read_txn()?;
+
+        for _ in 0..1000 {
+            let mut iter = db.iter(&mut rtxn)?;
+            assert_eq!(iter.next().transpose()?, Some((key1, val1)));
+            assert_eq!(iter.next().transpose()?, Some((key2, val2)));
+            assert_eq!(iter.next().transpose()?, None);
+        }
+
+        Ok(()) as heed3::Result<()>
+    });
+
+    for result in results {
+        result?;
+    }
+
+    eprintln!("Successful test!");
+
+    Ok(())
+}