Wallet and EsploraBlockchain are thread-safe*+

*If the user intends to use the `bdk::Wallet` concurrently, the user MUST
wrap `bdk::Wallet` with a `Mutex` of some sort. This is because BDK's
calls to `RefCell::borrow` and `RefCell::borrow_mut` assumed (implicitly
due to `bdk::Wallet` not being `Send` until this commit) that the user
was running `bdk::Wallet` in a single thread. Failure to keep calls to
`bdk::Wallet` mutually exclusive will result in panics when BDK
internally calls `try_lock().unwrap()` from multiple threads at once.

+If the user intends to use BDK using the async interface, the `Mutex`
that wraps `bdk::Wallet` must additionally be async-aware, such as
`futures::lock::Mutex` or `tokio::sync::Mutex`. This is because
`bdk::Wallet::sync` is async, and the lock on the `bdk::Wallet` needs to
be held across `.await`, and therefore the `MutexGuard` must be `Send` +
`Sync`.

Cargo.toml

@@ -12,7 +12,8 @@ readme = "README.md"
 license = "MIT OR Apache-2.0"
 
 [dependencies]
-bdk-macros = "^0.6"
+# bdk-macros = "^0.6"
+bdk-macros = { path = "macros", version = "^0.6" }
 log = "^0.4"
 miniscript = { version = "8.0", features = ["serde"] }
 bitcoin = { version = "0.29.1", features = ["serde", "base64", "rand"] }
@@ -111,6 +112,7 @@ electrsd = "0.21"
 # Move back to importing from rust-bitcoin once https://github.com/rust-bitcoin/rust-bitcoin/pull/1342 is released
 base64 = "^0.13"
 assert_matches = "1.5.0"
+tokio = "1"
 
 [[example]]
 name = "compact_filters_balance"

examples/utils/mod.rs

@@ -5,7 +5,7 @@ pub(crate) mod tx {
     use bdk::{database::BatchDatabase, SignOptions, Wallet};
     use bitcoin::{Address, Transaction};
 
-    pub fn build_signed_tx<D: BatchDatabase>(
+    pub fn build_signed_tx<D: BatchDatabase + Send>(
         wallet: &Wallet<D>,
         recipient_address: &str,
         amount: u64,

macros/src/lib.rs

@@ -33,7 +33,7 @@ fn add_async_trait(mut parsed: ItemTrait) -> TokenStream {
         #output
 
         #[cfg(any(target_arch = "wasm32", feature = "async-interface"))]
-        #[async_trait(?Send)]
+        #[async_trait]
         #parsed
     };
 
@@ -74,7 +74,7 @@ fn add_async_impl_trait(mut parsed: ItemImpl) -> TokenStream {
         #output
 
         #[cfg(any(target_arch = "wasm32", feature = "async-interface"))]
-        #[async_trait(?Send)]
+        #[async_trait]
         #parsed
     };
 

src/blockchain/any.rs

@@ -129,7 +129,7 @@ impl GetBlockHash for AnyBlockchain {
 
 #[maybe_async]
 impl WalletSync for AnyBlockchain {
-    fn wallet_sync<D: BatchDatabase>(
+    fn wallet_sync<D: BatchDatabase + Send + Sync>(
         &self,
         database: &mut D,
         progress_update: Box<dyn Progress>,
@@ -142,7 +142,7 @@ impl WalletSync for AnyBlockchain {
         ))
     }
 
-    fn wallet_setup<D: BatchDatabase>(
+    fn wallet_setup<D: BatchDatabase + Send + Sync>(
         &self,
         database: &mut D,
         progress_update: Box<dyn Progress>,

src/blockchain/esplora/async.rs

@@ -133,7 +133,7 @@ impl GetBlockHash for EsploraBlockchain {
 
 #[maybe_async]
 impl WalletSync for EsploraBlockchain {
-    fn wallet_setup<D: BatchDatabase>(
+    fn wallet_setup<D: BatchDatabase + Send + Sync>(
         &self,
         database: &mut D,
         _progress_update: Box<dyn Progress>,
@@ -248,3 +248,40 @@ impl ConfigurableBlockchain for EsploraBlockchain {
         Ok(blockchain)
     }
 }
+
+#[cfg(test)]
+mod test {
+    use std::sync::Arc;
+
+    use bitcoin::Network;
+
+    use crate::database::{AnyDatabase, MemoryDatabase};
+    use crate::wallet::test::get_test_wpkh;
+    use crate::SyncOptions;
+    use super::*;
+
+    /// A quick test that doesn't actually do anything, but will throw a compile
+    /// error if bdk::Wallet or EsploraBlockchain are not thread-safe.
+    #[tokio::test]
+    async fn esplora_async_wallet_is_thread_safe() {
+        tokio::task::spawn(async move {
+            let descriptors = testutils!(@descriptors (get_test_wpkh()));
+            let wallet = Wallet::new(
+                &descriptors.0,
+                None,
+                Network::Regtest,
+                AnyDatabase::Memory(MemoryDatabase::new()),
+            )
+            .unwrap();
+            let wrapped_wallet = Arc::new(tokio::sync::Mutex::new(wallet));
+
+            let esplora = EsploraBlockchain::new("localhost:8000", 20);
+            let sync_options = SyncOptions { progress: None };
+            let _ = wrapped_wallet
+                .lock()
+                .await
+                .sync(&esplora, sync_options)
+                .await;
+        });
+    }
+}

src/blockchain/mod.rs

@@ -131,7 +131,7 @@ pub trait WalletSync {
     /// For types that do not have that distinction, only this method can be implemented, since
     /// [`WalletSync::wallet_sync`] defaults to calling this internally if not overridden.
     /// Populate the internal database with transactions and UTXOs
-    fn wallet_setup<D: BatchDatabase>(
+    fn wallet_setup<D: BatchDatabase + Send + Sync>(
         &self,
         database: &mut D,
         progress_update: Box<dyn Progress>,
@@ -154,7 +154,7 @@ pub trait WalletSync {
     /// [`BatchOperations::set_tx`]: crate::database::BatchOperations::set_tx
     /// [`BatchOperations::set_utxo`]: crate::database::BatchOperations::set_utxo
     /// [`BatchOperations::del_utxo`]: crate::database::BatchOperations::del_utxo
-    fn wallet_sync<D: BatchDatabase>(
+    fn wallet_sync<D: BatchDatabase + Send + Sync>(
         &self,
         database: &mut D,
         progress_update: Box<dyn Progress>,
@@ -210,7 +210,7 @@ fn sum_of_balances<B: BlockchainFactory>(blockchain_factory: B, wallets: &[Walle
 )]
 pub trait BlockchainFactory {
     /// The type returned when building a blockchain from this factory
-    type Inner: Blockchain;
+    type Inner: Blockchain + Send + Sync;
 
     /// Build a new blockchain for the given descriptor wallet_name
     ///
@@ -227,7 +227,7 @@ pub trait BlockchainFactory {
     ///
     /// Internally uses [`wallet_name_from_descriptor`] to derive the name, and then calls
     /// [`BlockchainFactory::build`] to create the blockchain instance.
-    fn build_for_wallet<D: BatchDatabase>(
+    fn build_for_wallet<D: BatchDatabase + Send + Sync>(
         &self,
         wallet: &Wallet<D>,
         override_skip_blocks: Option<u32>,
@@ -253,7 +253,7 @@ pub trait BlockchainFactory {
         docsrs,
         doc(cfg(not(any(target_arch = "wasm32", feature = "async-interface"))))
     )]
-    fn sync_wallet<D: BatchDatabase>(
+    fn sync_wallet<D: BatchDatabase + Send>(
         &self,
         wallet: &Wallet<D>,
         override_skip_blocks: Option<u32>,
@@ -264,7 +264,7 @@ pub trait BlockchainFactory {
     }
 }
 
-impl<T: StatelessBlockchain> BlockchainFactory for Arc<T> {
+impl<T: StatelessBlockchain + Send + Sync> BlockchainFactory for Arc<T> {
     type Inner = Self;
 
     fn build(&self, _wallet_name: &str, _override_skip_blocks: Option<u32>) -> Result<Self, Error> {
@@ -338,7 +338,7 @@ impl Progress for LogProgress {
 }
 
 #[maybe_async]
-impl<T: Blockchain> Blockchain for Arc<T> {
+impl<T: Blockchain + Send + Sync> Blockchain for Arc<T> {
     fn get_capabilities(&self) -> HashSet<Capability> {
         maybe_await!(self.deref().get_capabilities())
     }
@@ -353,37 +353,37 @@ impl<T: Blockchain> Blockchain for Arc<T> {
 }
 
 #[maybe_async]
-impl<T: GetTx> GetTx for Arc<T> {
+impl<T: GetTx + Send + Sync> GetTx for Arc<T> {
     fn get_tx(&self, txid: &Txid) -> Result<Option<Transaction>, Error> {
         maybe_await!(self.deref().get_tx(txid))
     }
 }
 
 #[maybe_async]
-impl<T: GetHeight> GetHeight for Arc<T> {
+impl<T: GetHeight + Send + Sync> GetHeight for Arc<T> {
     fn get_height(&self) -> Result<u32, Error> {
         maybe_await!(self.deref().get_height())
     }
 }
 
 #[maybe_async]
-impl<T: GetBlockHash> GetBlockHash for Arc<T> {
+impl<T: GetBlockHash + Send + Sync> GetBlockHash for Arc<T> {
     fn get_block_hash(&self, height: u64) -> Result<BlockHash, Error> {
         maybe_await!(self.deref().get_block_hash(height))
     }
 }
 
 #[maybe_async]
-impl<T: WalletSync> WalletSync for Arc<T> {
-    fn wallet_setup<D: BatchDatabase>(
+impl<T: WalletSync + Send + Sync> WalletSync for Arc<T> {
+    fn wallet_setup<D: BatchDatabase + Send + Sync>(
         &self,
         database: &mut D,
         progress_update: Box<dyn Progress>,
     ) -> Result<(), Error> {
         maybe_await!(self.deref().wallet_setup(database, progress_update))
     }
 
-    fn wallet_sync<D: BatchDatabase>(
+    fn wallet_sync<D: BatchDatabase + Send + Sync>(
         &self,
         database: &mut D,
         progress_update: Box<dyn Progress>,

src/database/mod.rs

@@ -165,7 +165,7 @@ pub trait Database: BatchOperations {
 /// This trait defines the methods to start and apply a batch of operations.
 pub trait BatchDatabase: Database {
     /// Container for the operations
-    type Batch: BatchOperations;
+    type Batch: BatchOperations + Send;
 
     /// Create a new batch container
     fn begin_batch(&self) -> Self::Batch;

src/wallet/export.rs

@@ -116,7 +116,7 @@ impl FullyNodedExport {
     ///
     /// If the database is empty or `include_blockheight` is false, the `blockheight` field
     /// returned will be `0`.
-    pub fn export_wallet<D: BatchDatabase>(
+    pub fn export_wallet<D: BatchDatabase + Send + Sync>(
         wallet: &Wallet<D>,
         label: &str,
         include_blockheight: bool,

src/wallet/mod.rs

@@ -169,7 +169,7 @@ pub struct SyncOptions {
 
 impl<D> Wallet<D>
 where
-    D: BatchDatabase,
+    D: BatchDatabase + Send + Sync,
 {
     #[deprecated = "Just use Wallet::new -- all wallets are offline now!"]
     /// Create a new "offline" wallet
@@ -1687,7 +1687,7 @@ where
 
     /// Sync the internal database with the blockchain
     #[maybe_async]
-    pub fn sync<B: WalletSync + GetHeight>(
+    pub fn sync<B: WalletSync + GetHeight + Send + Sync>(
         &self,
         blockchain: &B,
         sync_opts: SyncOptions,

src/wallet/tx_builder.rs

@@ -179,7 +179,7 @@ impl<'a, Cs: Clone, Ctx, D> Clone for TxBuilder<'a, D, Cs, Ctx> {
 }
 
 // methods supported by both contexts, for any CoinSelectionAlgorithm
-impl<'a, D: BatchDatabase, Cs: CoinSelectionAlgorithm<D>, Ctx: TxBuilderContext>
+impl<'a, D: BatchDatabase + Send + Sync, Cs: CoinSelectionAlgorithm<D>, Ctx: TxBuilderContext>
     TxBuilder<'a, D, Cs, Ctx>
 {
     /// Set a custom fee rate