Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 773 insertions, 0 deletions

diff --git a/third_party/rust/lmdb-rkv/src/transaction.rs b/third_party/rust/lmdb-rkv/src/transaction.rs
new file mode 100644
index 0000000000..a1d01f86cc
--- /dev/null
+++ b/third_party/rust/lmdb-rkv/src/transaction.rs
@@ -0,0 +1,773 @@
+use libc::{
+    c_uint,
+    c_void,
+    size_t,
+};
+use std::marker::PhantomData;
+use std::{
+    fmt,
+    mem,
+    ptr,
+    result,
+    slice,
+};
+
+use ffi;
+
+use cursor::{
+    RoCursor,
+    RwCursor,
+};
+use database::Database;
+use environment::{
+    Environment,
+    Stat,
+};
+use error::{
+    lmdb_result,
+    Error,
+    Result,
+};
+use flags::{
+    DatabaseFlags,
+    EnvironmentFlags,
+    WriteFlags,
+};
+
+/// An LMDB transaction.
+///
+/// All database operations require a transaction.
+pub trait Transaction: Sized {
+    /// Returns a raw pointer to the underlying LMDB transaction.
+    ///
+    /// The caller **must** ensure that the pointer is not used after the
+    /// lifetime of the transaction.
+    fn txn(&self) -> *mut ffi::MDB_txn;
+
+    /// Commits the transaction.
+    ///
+    /// Any pending operations will be saved.
+    fn commit(self) -> Result<()> {
+        unsafe {
+            let result = lmdb_result(ffi::mdb_txn_commit(self.txn()));
+            mem::forget(self);
+            result
+        }
+    }
+
+    /// Aborts the transaction.
+    ///
+    /// Any pending operations will not be saved.
+    fn abort(self) {
+        // Abort should be performed in transaction destructors.
+    }
+
+    /// Opens a database in the transaction.
+    ///
+    /// If `name` is `None`, then the default database will be opened, otherwise
+    /// a named database will be opened. The database handle will be private to
+    /// the transaction until the transaction is successfully committed. If the
+    /// transaction is aborted the returned database handle should no longer be
+    /// used.
+    ///
+    /// Prefer using `Environment::open_db`.
+    ///
+    /// ## Safety
+    ///
+    /// This function (as well as `Environment::open_db`,
+    /// `Environment::create_db`, and `Database::create`) **must not** be called
+    /// from multiple concurrent transactions in the same environment. A
+    /// transaction which uses this function must finish (either commit or
+    /// abort) before any other transaction may use this function.
+    unsafe fn open_db(&self, name: Option<&str>) -> Result<Database> {
+        Database::new(self.txn(), name, 0)
+    }
+
+    /// Gets an item from a database.
+    ///
+    /// This function retrieves the data associated with the given key in the
+    /// database. If the database supports duplicate keys
+    /// (`DatabaseFlags::DUP_SORT`) then the first data item for the key will be
+    /// returned. Retrieval of other items requires the use of
+    /// `Transaction::cursor_get`. If the item is not in the database, then
+    /// `Error::NotFound` will be returned.
+    fn get<'txn, K>(&'txn self, database: Database, key: &K) -> Result<&'txn [u8]>
+    where
+        K: AsRef<[u8]>,
+    {
+        let key = key.as_ref();
+        let mut key_val: ffi::MDB_val = ffi::MDB_val {
+            mv_size: key.len() as size_t,
+            mv_data: key.as_ptr() as *mut c_void,
+        };
+        let mut data_val: ffi::MDB_val = ffi::MDB_val {
+            mv_size: 0,
+            mv_data: ptr::null_mut(),
+        };
+        unsafe {
+            match ffi::mdb_get(self.txn(), database.dbi(), &mut key_val, &mut data_val) {
+                ffi::MDB_SUCCESS => Ok(slice::from_raw_parts(data_val.mv_data as *const u8, data_val.mv_size as usize)),
+                err_code => Err(Error::from_err_code(err_code)),
+            }
+        }
+    }
+
+    /// Open a new read-only cursor on the given database.
+    fn open_ro_cursor<'txn>(&'txn self, db: Database) -> Result<RoCursor<'txn>> {
+        RoCursor::new(self, db)
+    }
+
+    /// Gets the option flags for the given database in the transaction.
+    fn db_flags(&self, db: Database) -> Result<DatabaseFlags> {
+        let mut flags: c_uint = 0;
+        unsafe {
+            lmdb_result(ffi::mdb_dbi_flags(self.txn(), db.dbi(), &mut flags))?;
+        }
+        Ok(DatabaseFlags::from_bits_truncate(flags))
+    }
+
+    /// Retrieves database statistics.
+    fn stat(&self, db: Database) -> Result<Stat> {
+        unsafe {
+            let mut stat = Stat::new();
+            lmdb_try!(ffi::mdb_stat(self.txn(), db.dbi(), stat.mdb_stat()));
+            Ok(stat)
+        }
+    }
+}
+
+/// An LMDB read-only transaction.
+pub struct RoTransaction<'env> {
+    txn: *mut ffi::MDB_txn,
+    _marker: PhantomData<&'env ()>,
+}
+
+impl<'env> fmt::Debug for RoTransaction<'env> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> result::Result<(), fmt::Error> {
+        f.debug_struct("RoTransaction").finish()
+    }
+}
+
+impl<'env> Drop for RoTransaction<'env> {
+    fn drop(&mut self) {
+        unsafe { ffi::mdb_txn_abort(self.txn) }
+    }
+}
+
+impl<'env> RoTransaction<'env> {
+    /// Creates a new read-only transaction in the given environment. Prefer
+    /// using `Environment::begin_ro_txn`.
+    pub(crate) fn new(env: &'env Environment) -> Result<RoTransaction<'env>> {
+        let mut txn: *mut ffi::MDB_txn = ptr::null_mut();
+        unsafe {
+            lmdb_result(ffi::mdb_txn_begin(env.env(), ptr::null_mut(), ffi::MDB_RDONLY, &mut txn))?;
+            Ok(RoTransaction {
+                txn,
+                _marker: PhantomData,
+            })
+        }
+    }
+
+    /// Resets the read-only transaction.
+    ///
+    /// Abort the transaction like `Transaction::abort`, but keep the
+    /// transaction handle.  `InactiveTransaction::renew` may reuse the handle.
+    /// This saves allocation overhead if the process will start a new read-only
+    /// transaction soon, and also locking overhead if
+    /// `EnvironmentFlags::NO_TLS` is in use. The reader table lock is released,
+    /// but the table slot stays tied to its thread or transaction. Reader locks
+    /// generally don't interfere with writers, but they keep old versions of
+    /// database pages allocated. Thus they prevent the old pages from being
+    /// reused when writers commit new data, and so under heavy load the
+    /// database size may grow much more rapidly than otherwise.
+    pub fn reset(self) -> InactiveTransaction<'env> {
+        let txn = self.txn;
+        unsafe {
+            mem::forget(self);
+            ffi::mdb_txn_reset(txn)
+        };
+        InactiveTransaction {
+            txn,
+            _marker: PhantomData,
+        }
+    }
+}
+
+impl<'env> Transaction for RoTransaction<'env> {
+    fn txn(&self) -> *mut ffi::MDB_txn {
+        self.txn
+    }
+}
+
+/// An inactive read-only transaction.
+pub struct InactiveTransaction<'env> {
+    txn: *mut ffi::MDB_txn,
+    _marker: PhantomData<&'env ()>,
+}
+
+impl<'env> fmt::Debug for InactiveTransaction<'env> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> result::Result<(), fmt::Error> {
+        f.debug_struct("InactiveTransaction").finish()
+    }
+}
+
+impl<'env> Drop for InactiveTransaction<'env> {
+    fn drop(&mut self) {
+        unsafe { ffi::mdb_txn_abort(self.txn) }
+    }
+}
+
+impl<'env> InactiveTransaction<'env> {
+    /// Renews the inactive transaction, returning an active read-only
+    /// transaction.
+    ///
+    /// This acquires a new reader lock for a transaction handle that had been
+    /// released by `RoTransaction::reset`.
+    pub fn renew(self) -> Result<RoTransaction<'env>> {
+        let txn = self.txn;
+        unsafe {
+            mem::forget(self);
+            lmdb_result(ffi::mdb_txn_renew(txn))?
+        };
+        Ok(RoTransaction {
+            txn,
+            _marker: PhantomData,
+        })
+    }
+}
+
+/// An LMDB read-write transaction.
+pub struct RwTransaction<'env> {
+    txn: *mut ffi::MDB_txn,
+    _marker: PhantomData<&'env ()>,
+}
+
+impl<'env> fmt::Debug for RwTransaction<'env> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> result::Result<(), fmt::Error> {
+        f.debug_struct("RwTransaction").finish()
+    }
+}
+
+impl<'env> Drop for RwTransaction<'env> {
+    fn drop(&mut self) {
+        unsafe { ffi::mdb_txn_abort(self.txn) }
+    }
+}
+
+impl<'env> RwTransaction<'env> {
+    /// Creates a new read-write transaction in the given environment. Prefer
+    /// using `Environment::begin_ro_txn`.
+    pub(crate) fn new(env: &'env Environment) -> Result<RwTransaction<'env>> {
+        let mut txn: *mut ffi::MDB_txn = ptr::null_mut();
+        unsafe {
+            lmdb_result(ffi::mdb_txn_begin(env.env(), ptr::null_mut(), EnvironmentFlags::empty().bits(), &mut txn))?;
+            Ok(RwTransaction {
+                txn,
+                _marker: PhantomData,
+            })
+        }
+    }
+
+    /// Opens a database in the provided transaction, creating it if necessary.
+    ///
+    /// If `name` is `None`, then the default database will be opened, otherwise
+    /// a named database will be opened. The database handle will be private to
+    /// the transaction until the transaction is successfully committed. If the
+    /// transaction is aborted the returned database handle should no longer be
+    /// used.
+    ///
+    /// Prefer using `Environment::create_db`.
+    ///
+    /// ## Safety
+    ///
+    /// This function (as well as `Environment::open_db`,
+    /// `Environment::create_db`, and `Database::open`) **must not** be called
+    /// from multiple concurrent transactions in the same environment. A
+    /// transaction which uses this function must finish (either commit or
+    /// abort) before any other transaction may use this function.
+    pub unsafe fn create_db(&self, name: Option<&str>, flags: DatabaseFlags) -> Result<Database> {
+        Database::new(self.txn(), name, flags.bits() | ffi::MDB_CREATE)
+    }
+
+    /// Opens a new read-write cursor on the given database and transaction.
+    pub fn open_rw_cursor<'txn>(&'txn mut self, db: Database) -> Result<RwCursor<'txn>> {
+        RwCursor::new(self, db)
+    }
+
+    /// Stores an item into a database.
+    ///
+    /// This function stores key/data pairs in the database. The default
+    /// behavior is to enter the new key/data pair, replacing any previously
+    /// existing key if duplicates are disallowed, or adding a duplicate data
+    /// item if duplicates are allowed (`DatabaseFlags::DUP_SORT`).
+    pub fn put<K, D>(&mut self, database: Database, key: &K, data: &D, flags: WriteFlags) -> Result<()>
+    where
+        K: AsRef<[u8]>,
+        D: AsRef<[u8]>,
+    {
+        let key = key.as_ref();
+        let data = data.as_ref();
+        let mut key_val: ffi::MDB_val = ffi::MDB_val {
+            mv_size: key.len() as size_t,
+            mv_data: key.as_ptr() as *mut c_void,
+        };
+        let mut data_val: ffi::MDB_val = ffi::MDB_val {
+            mv_size: data.len() as size_t,
+            mv_data: data.as_ptr() as *mut c_void,
+        };
+        unsafe { lmdb_result(ffi::mdb_put(self.txn(), database.dbi(), &mut key_val, &mut data_val, flags.bits())) }
+    }
+
+    /// Returns a buffer which can be used to write a value into the item at the
+    /// given key and with the given length. The buffer must be completely
+    /// filled by the caller.
+    pub fn reserve<'txn, K>(
+        &'txn mut self,
+        database: Database,
+        key: &K,
+        len: size_t,
+        flags: WriteFlags,
+    ) -> Result<&'txn mut [u8]>
+    where
+        K: AsRef<[u8]>,
+    {
+        let key = key.as_ref();
+        let mut key_val: ffi::MDB_val = ffi::MDB_val {
+            mv_size: key.len() as size_t,
+            mv_data: key.as_ptr() as *mut c_void,
+        };
+        let mut data_val: ffi::MDB_val = ffi::MDB_val {
+            mv_size: len,
+            mv_data: ptr::null_mut::<c_void>(),
+        };
+        unsafe {
+            lmdb_result(ffi::mdb_put(
+                self.txn(),
+                database.dbi(),
+                &mut key_val,
+                &mut data_val,
+                flags.bits() | ffi::MDB_RESERVE,
+            ))?;
+            Ok(slice::from_raw_parts_mut(data_val.mv_data as *mut u8, data_val.mv_size as usize))
+        }
+    }
+
+    /// Deletes an item from a database.
+    ///
+    /// This function removes key/data pairs from the database. If the database
+    /// does not support sorted duplicate data items (`DatabaseFlags::DUP_SORT`)
+    /// the data parameter is ignored.  If the database supports sorted
+    /// duplicates and the data parameter is `None`, all of the duplicate data
+    /// items for the key will be deleted. Otherwise, if the data parameter is
+    /// `Some` only the matching data item will be deleted. This function will
+    /// return `Error::NotFound` if the specified key/data pair is not in the
+    /// database.
+    pub fn del<K>(&mut self, database: Database, key: &K, data: Option<&[u8]>) -> Result<()>
+    where
+        K: AsRef<[u8]>,
+    {
+        let key = key.as_ref();
+        let mut key_val: ffi::MDB_val = ffi::MDB_val {
+            mv_size: key.len() as size_t,
+            mv_data: key.as_ptr() as *mut c_void,
+        };
+        let data_val: Option<ffi::MDB_val> = data.map(|data| ffi::MDB_val {
+            mv_size: data.len() as size_t,
+            mv_data: data.as_ptr() as *mut c_void,
+        });
+
+        if let Some(mut d) = data_val {
+            unsafe { lmdb_result(ffi::mdb_del(self.txn(), database.dbi(), &mut key_val, &mut d)) }
+        } else {
+            unsafe { lmdb_result(ffi::mdb_del(self.txn(), database.dbi(), &mut key_val, ptr::null_mut())) }
+        }
+    }
+
+    /// Empties the given database. All items will be removed.
+    pub fn clear_db(&mut self, db: Database) -> Result<()> {
+        unsafe { lmdb_result(ffi::mdb_drop(self.txn(), db.dbi(), 0)) }
+    }
+
+    /// Drops the database from the environment.
+    ///
+    /// ## Safety
+    ///
+    /// This method is unsafe in the same ways as `Environment::close_db`, and
+    /// should be used accordingly.
+    pub unsafe fn drop_db(&mut self, db: Database) -> Result<()> {
+        lmdb_result(ffi::mdb_drop(self.txn, db.dbi(), 1))
+    }
+
+    /// Begins a new nested transaction inside of this transaction.
+    pub fn begin_nested_txn<'txn>(&'txn mut self) -> Result<RwTransaction<'txn>> {
+        let mut nested: *mut ffi::MDB_txn = ptr::null_mut();
+        unsafe {
+            let env: *mut ffi::MDB_env = ffi::mdb_txn_env(self.txn());
+            ffi::mdb_txn_begin(env, self.txn(), 0, &mut nested);
+        }
+        Ok(RwTransaction {
+            txn: nested,
+            _marker: PhantomData,
+        })
+    }
+}
+
+impl<'env> Transaction for RwTransaction<'env> {
+    fn txn(&self) -> *mut ffi::MDB_txn {
+        self.txn
+    }
+}
+
+#[cfg(test)]
+mod test {
+
+    use std::io::Write;
+    use std::sync::{
+        Arc,
+        Barrier,
+    };
+    use std::thread::{
+        self,
+        JoinHandle,
+    };
+
+    use tempdir::TempDir;
+
+    use super::*;
+    use cursor::Cursor;
+    use error::*;
+    use flags::*;
+
+    #[test]
+    fn test_put_get_del() {
+        let dir = TempDir::new("test").unwrap();
+        let env = Environment::new().open(dir.path()).unwrap();
+        let db = env.open_db(None).unwrap();
+
+        let mut txn = env.begin_rw_txn().unwrap();
+        txn.put(db, b"key1", b"val1", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key2", b"val2", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key3", b"val3", WriteFlags::empty()).unwrap();
+        txn.commit().unwrap();
+
+        let mut txn = env.begin_rw_txn().unwrap();
+        assert_eq!(b"val1", txn.get(db, b"key1").unwrap());
+        assert_eq!(b"val2", txn.get(db, b"key2").unwrap());
+        assert_eq!(b"val3", txn.get(db, b"key3").unwrap());
+        assert_eq!(txn.get(db, b"key"), Err(Error::NotFound));
+
+        txn.del(db, b"key1", None).unwrap();
+        assert_eq!(txn.get(db, b"key1"), Err(Error::NotFound));
+    }
+
+    #[test]
+    fn test_put_get_del_multi() {
+        let dir = TempDir::new("test").unwrap();
+        let env = Environment::new().open(dir.path()).unwrap();
+        let db = env.create_db(None, DatabaseFlags::DUP_SORT).unwrap();
+
+        let mut txn = env.begin_rw_txn().unwrap();
+        txn.put(db, b"key1", b"val1", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key1", b"val2", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key1", b"val3", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key2", b"val1", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key2", b"val2", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key2", b"val3", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key3", b"val1", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key3", b"val2", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key3", b"val3", WriteFlags::empty()).unwrap();
+        txn.commit().unwrap();
+
+        let txn = env.begin_rw_txn().unwrap();
+        {
+            let mut cur = txn.open_ro_cursor(db).unwrap();
+            let iter = cur.iter_dup_of(b"key1");
+            let vals = iter.map(|x| x.unwrap()).map(|(_, x)| x).collect::<Vec<_>>();
+            assert_eq!(vals, vec![b"val1", b"val2", b"val3"]);
+        }
+        txn.commit().unwrap();
+
+        let mut txn = env.begin_rw_txn().unwrap();
+        txn.del(db, b"key1", Some(b"val2")).unwrap();
+        txn.del(db, b"key2", None).unwrap();
+        txn.commit().unwrap();
+
+        let txn = env.begin_rw_txn().unwrap();
+        {
+            let mut cur = txn.open_ro_cursor(db).unwrap();
+            let iter = cur.iter_dup_of(b"key1");
+            let vals = iter.map(|x| x.unwrap()).map(|(_, x)| x).collect::<Vec<_>>();
+            assert_eq!(vals, vec![b"val1", b"val3"]);
+
+            let iter = cur.iter_dup_of(b"key2");
+            assert_eq!(0, iter.count());
+        }
+        txn.commit().unwrap();
+    }
+
+    #[test]
+    fn test_reserve() {
+        let dir = TempDir::new("test").unwrap();
+        let env = Environment::new().open(dir.path()).unwrap();
+        let db = env.open_db(None).unwrap();
+
+        let mut txn = env.begin_rw_txn().unwrap();
+        {
+            let mut writer = txn.reserve(db, b"key1", 4, WriteFlags::empty()).unwrap();
+            writer.write_all(b"val1").unwrap();
+        }
+        txn.commit().unwrap();
+
+        let mut txn = env.begin_rw_txn().unwrap();
+        assert_eq!(b"val1", txn.get(db, b"key1").unwrap());
+        assert_eq!(txn.get(db, b"key"), Err(Error::NotFound));
+
+        txn.del(db, b"key1", None).unwrap();
+        assert_eq!(txn.get(db, b"key1"), Err(Error::NotFound));
+    }
+
+    #[test]
+    fn test_inactive_txn() {
+        let dir = TempDir::new("test").unwrap();
+        let env = Environment::new().open(dir.path()).unwrap();
+        let db = env.open_db(None).unwrap();
+
+        {
+            let mut txn = env.begin_rw_txn().unwrap();
+            txn.put(db, b"key", b"val", WriteFlags::empty()).unwrap();
+            txn.commit().unwrap();
+        }
+
+        let txn = env.begin_ro_txn().unwrap();
+        let inactive = txn.reset();
+        let active = inactive.renew().unwrap();
+        assert!(active.get(db, b"key").is_ok());
+    }
+
+    #[test]
+    fn test_nested_txn() {
+        let dir = TempDir::new("test").unwrap();
+        let env = Environment::new().open(dir.path()).unwrap();
+        let db = env.open_db(None).unwrap();
+
+        let mut txn = env.begin_rw_txn().unwrap();
+        txn.put(db, b"key1", b"val1", WriteFlags::empty()).unwrap();
+
+        {
+            let mut nested = txn.begin_nested_txn().unwrap();
+            nested.put(db, b"key2", b"val2", WriteFlags::empty()).unwrap();
+            assert_eq!(nested.get(db, b"key1").unwrap(), b"val1");
+            assert_eq!(nested.get(db, b"key2").unwrap(), b"val2");
+        }
+
+        assert_eq!(txn.get(db, b"key1").unwrap(), b"val1");
+        assert_eq!(txn.get(db, b"key2"), Err(Error::NotFound));
+    }
+
+    #[test]
+    fn test_clear_db() {
+        let dir = TempDir::new("test").unwrap();
+        let env = Environment::new().open(dir.path()).unwrap();
+        let db = env.open_db(None).unwrap();
+
+        {
+            let mut txn = env.begin_rw_txn().unwrap();
+            txn.put(db, b"key", b"val", WriteFlags::empty()).unwrap();
+            txn.commit().unwrap();
+        }
+
+        {
+            let mut txn = env.begin_rw_txn().unwrap();
+            txn.clear_db(db).unwrap();
+            txn.commit().unwrap();
+        }
+
+        let txn = env.begin_ro_txn().unwrap();
+        assert_eq!(txn.get(db, b"key"), Err(Error::NotFound));
+    }
+
+    #[test]
+    fn test_drop_db() {
+        let dir = TempDir::new("test").unwrap();
+        let env = Environment::new().set_max_dbs(2).open(dir.path()).unwrap();
+        let db = env.create_db(Some("test"), DatabaseFlags::empty()).unwrap();
+
+        {
+            let mut txn = env.begin_rw_txn().unwrap();
+            txn.put(db, b"key", b"val", WriteFlags::empty()).unwrap();
+            txn.commit().unwrap();
+        }
+        {
+            let mut txn = env.begin_rw_txn().unwrap();
+            unsafe {
+                txn.drop_db(db).unwrap();
+            }
+            txn.commit().unwrap();
+        }
+
+        assert_eq!(env.open_db(Some("test")), Err(Error::NotFound));
+    }
+
+    #[test]
+    fn test_concurrent_readers_single_writer() {
+        let dir = TempDir::new("test").unwrap();
+        let env: Arc<Environment> = Arc::new(Environment::new().open(dir.path()).unwrap());
+
+        let n = 10usize; // Number of concurrent readers
+        let barrier = Arc::new(Barrier::new(n + 1));
+        let mut threads: Vec<JoinHandle<bool>> = Vec::with_capacity(n);
+
+        let key = b"key";
+        let val = b"val";
+
+        for _ in 0..n {
+            let reader_env = env.clone();
+            let reader_barrier = barrier.clone();
+
+            threads.push(thread::spawn(move || {
+                let db = reader_env.open_db(None).unwrap();
+                {
+                    let txn = reader_env.begin_ro_txn().unwrap();
+                    assert_eq!(txn.get(db, key), Err(Error::NotFound));
+                    txn.abort();
+                }
+                reader_barrier.wait();
+                reader_barrier.wait();
+                {
+                    let txn = reader_env.begin_ro_txn().unwrap();
+                    txn.get(db, key).unwrap() == val
+                }
+            }));
+        }
+
+        let db = env.open_db(None).unwrap();
+        let mut txn = env.begin_rw_txn().unwrap();
+        barrier.wait();
+        txn.put(db, key, val, WriteFlags::empty()).unwrap();
+        txn.commit().unwrap();
+        barrier.wait();
+
+        assert!(threads.into_iter().all(|b| b.join().unwrap()))
+    }
+
+    #[test]
+    fn test_concurrent_writers() {
+        let dir = TempDir::new("test").unwrap();
+        let env = Arc::new(Environment::new().open(dir.path()).unwrap());
+
+        let n = 10usize; // Number of concurrent writers
+        let mut threads: Vec<JoinHandle<bool>> = Vec::with_capacity(n);
+
+        let key = "key";
+        let val = "val";
+
+        for i in 0..n {
+            let writer_env = env.clone();
+
+            threads.push(thread::spawn(move || {
+                let db = writer_env.open_db(None).unwrap();
+                let mut txn = writer_env.begin_rw_txn().unwrap();
+                txn.put(db, &format!("{}{}", key, i), &format!("{}{}", val, i), WriteFlags::empty()).unwrap();
+                txn.commit().is_ok()
+            }));
+        }
+        assert!(threads.into_iter().all(|b| b.join().unwrap()));
+
+        let db = env.open_db(None).unwrap();
+        let txn = env.begin_ro_txn().unwrap();
+
+        for i in 0..n {
+            assert_eq!(format!("{}{}", val, i).as_bytes(), txn.get(db, &format!("{}{}", key, i)).unwrap());
+        }
+    }
+
+    #[test]
+    fn test_stat() {
+        let dir = TempDir::new("test").unwrap();
+        let env = Environment::new().open(dir.path()).unwrap();
+        let db = env.create_db(None, DatabaseFlags::empty()).unwrap();
+
+        let mut txn = env.begin_rw_txn().unwrap();
+        txn.put(db, b"key1", b"val1", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key2", b"val2", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key3", b"val3", WriteFlags::empty()).unwrap();
+        txn.commit().unwrap();
+
+        {
+            let txn = env.begin_ro_txn().unwrap();
+            let stat = txn.stat(db).unwrap();
+            assert_eq!(stat.entries(), 3);
+        }
+
+        let mut txn = env.begin_rw_txn().unwrap();
+        txn.del(db, b"key1", None).unwrap();
+        txn.del(db, b"key2", None).unwrap();
+        txn.commit().unwrap();
+
+        {
+            let txn = env.begin_ro_txn().unwrap();
+            let stat = txn.stat(db).unwrap();
+            assert_eq!(stat.entries(), 1);
+        }
+
+        let mut txn = env.begin_rw_txn().unwrap();
+        txn.put(db, b"key4", b"val4", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key5", b"val5", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key6", b"val6", WriteFlags::empty()).unwrap();
+        txn.commit().unwrap();
+
+        {
+            let txn = env.begin_ro_txn().unwrap();
+            let stat = txn.stat(db).unwrap();
+            assert_eq!(stat.entries(), 4);
+        }
+    }
+
+    #[test]
+    fn test_stat_dupsort() {
+        let dir = TempDir::new("test").unwrap();
+        let env = Environment::new().open(dir.path()).unwrap();
+        let db = env.create_db(None, DatabaseFlags::DUP_SORT).unwrap();
+
+        let mut txn = env.begin_rw_txn().unwrap();
+        txn.put(db, b"key1", b"val1", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key1", b"val2", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key1", b"val3", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key2", b"val1", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key2", b"val2", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key2", b"val3", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key3", b"val1", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key3", b"val2", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key3", b"val3", WriteFlags::empty()).unwrap();
+        txn.commit().unwrap();
+
+        {
+            let txn = env.begin_ro_txn().unwrap();
+            let stat = txn.stat(db).unwrap();
+            assert_eq!(stat.entries(), 9);
+        }
+
+        let mut txn = env.begin_rw_txn().unwrap();
+        txn.del(db, b"key1", Some(b"val2")).unwrap();
+        txn.del(db, b"key2", None).unwrap();
+        txn.commit().unwrap();
+
+        {
+            let txn = env.begin_ro_txn().unwrap();
+            let stat = txn.stat(db).unwrap();
+            assert_eq!(stat.entries(), 5);
+        }
+
+        let mut txn = env.begin_rw_txn().unwrap();
+        txn.put(db, b"key4", b"val1", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key4", b"val2", WriteFlags::empty()).unwrap();
+        txn.put(db, b"key4", b"val3", WriteFlags::empty()).unwrap();
+        txn.commit().unwrap();
+
+        {
+            let txn = env.begin_ro_txn().unwrap();
+            let stat = txn.stat(db).unwrap();
+            assert_eq!(stat.entries(), 8);
+        }
+    }
+}