rpc: Use the blocks pinning API for chainHead methods (#13233)

* rpc/chain_head: Add backend to subscription management

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* rpc/chain_head: Pin blocks internally and adjust testing

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* client/in_mem: Reference for the number of pinned blocks

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* rpc/tests: Check in-memory references to pinned blocks

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* rpc/chain_head: Fix clippy

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* rpc/chain_head: Remove unused comment

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* rpc/chain_head: Place subscription handle under `Arc` and unpin blocks on drop

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* rpc/tests: Check all pinned blocks are unpinned on drop

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <git@kchr.de>

* Update client/rpc-spec-v2/src/chain_head/subscription.rs

Co-authored-by: Bastian Köcher <git@kchr.de>

* rpc/tests: Retry fetching the pinned references for CI correctness

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* client/service: Use 512 as maximum number of pinned blocks

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* chain_head: Fix merging conflicts

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* rpc/chain_head: Adjust subscriptions to use pinning API

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* rpc/chain_head/tests: Test subscription management

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* rpc/chain_head: Adjust chain_head follow to the new API

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* rpc/chain_head: Adjust chain_head.rs to the new API

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* rpc/chain_head/tests: Adjust test.rs to the new API

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* client/builder: Use new chainHead API

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* rpc/chain_head: Fix documentation

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* rpc/chain_head: Fix clippy

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* client/in_mem: ChainHead no longer uses `in_mem::children`

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Update client/rpc-spec-v2/src/chain_head/subscription.rs

Co-authored-by: Sebastian Kunert <skunert49@gmail.com>

* Update client/rpc-spec-v2/src/chain_head/subscription.rs

Co-authored-by: Sebastian Kunert <skunert49@gmail.com>

* Update client/rpc-spec-v2/src/chain_head/subscription.rs

Co-authored-by: Sebastian Kunert <skunert49@gmail.com>

* Update client/rpc-spec-v2/src/chain_head/subscription.rs

Co-authored-by: Sebastian Kunert <skunert49@gmail.com>

* chain_head: Add block state machine

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Address feedback

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Use new_native_or_wasm_executor

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* chain_head: Remove 'static on Backend

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* chain_head: Add documentation

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* chain_head: Lock blocks before async blocks

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* chain_head_follower: Remove static on backend

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Update client/service/src/builder.rs

Co-authored-by: Davide Galassi <davxy@datawok.net>

* Update client/service/src/builder.rs

Co-authored-by: Davide Galassi <davxy@datawok.net>

* chain_head: Add BlockHeaderAbsent to the PartialEq impl

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* client: Add better documentation around pinning constants

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* chain_head: Move subscription to dedicated module

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* subscription: Rename global pin / unpin functions

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

---------

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>
Co-authored-by: Bastian Köcher <git@kchr.de>
Co-authored-by: parity-processbot <>
Co-authored-by: Sebastian Kunert <skunert49@gmail.com>
Co-authored-by: Davide Galassi <davxy@datawok.net>

substrate/client/api/src/in_mem.rs

@@ -618,6 +618,7 @@ where
 	states: RwLock<HashMap<Block::Hash, InMemoryBackend<HashFor<Block>>>>,
 	blockchain: Blockchain<Block>,
 	import_lock: RwLock<()>,
+	pinned_blocks: RwLock<HashMap<Block::Hash, i64>>,
 }
 
 impl<Block: BlockT> Backend<Block>
@@ -625,13 +626,28 @@ where
 	Block::Hash: Ord,
 {
 	/// Create a new instance of in-mem backend.
+	///
+	/// # Warning
+	///
+	/// For testing purposes only!
 	pub fn new() -> Self {
 		Backend {
 			states: RwLock::new(HashMap::new()),
 			blockchain: Blockchain::new(),
 			import_lock: Default::default(),
+			pinned_blocks: Default::default(),
 		}
 	}
+
+	/// Return the number of references active for a pinned block.
+	///
+	/// # Warning
+	///
+	/// For testing purposes only!
+	pub fn pin_refs(&self, hash: &<Block as BlockT>::Hash) -> Option<i64> {
+		let blocks = self.pinned_blocks.read();
+		blocks.get(hash).map(|value| *value)
+	}
 }
 
 impl<Block: BlockT> backend::AuxStore for Backend<Block>
@@ -781,11 +797,16 @@ where
 		false
 	}
 
-	fn pin_block(&self, _: <Block as BlockT>::Hash) -> blockchain::Result<()> {
+	fn pin_block(&self, hash: <Block as BlockT>::Hash) -> blockchain::Result<()> {
+		let mut blocks = self.pinned_blocks.write();
+		*blocks.entry(hash).or_default() += 1;
 		Ok(())
 	}
 
-	fn unpin_block(&self, _: <Block as BlockT>::Hash) {}
+	fn unpin_block(&self, hash: <Block as BlockT>::Hash) {
+		let mut blocks = self.pinned_blocks.write();
+		blocks.entry(hash).and_modify(|counter| *counter -= 1).or_insert(-1);
+	}
 }
 
 impl<Block: BlockT> backend::LocalBackend<Block> for Backend<Block> where Block::Hash: Ord {}