Fair reusing of wasm runtime instances (#3011)

* Add test from original bug report

Original is from @pepyakin in 3d7b27f3421818e8d6de568e02fbc2947a06246b.
I adapted it to work with the latest master.

* No longer cleanup module instance

* Replace runtime cache with synchronous clone

* Fix test

* Preserve initial runtime memory and restore it on fetch

* Remove leftover comment

* Fix style

* Improve variable naming

* Replace get_into() with get()

* Handle missing memory export better

* Return earlier when creating runtime first time

* Improve comments

* fmt

* Fix #2967.

* Eradicate `code` from `Error::InvalidCode`

* tidy

* A state snapshot doc.

* Store multiple runtimes by hash.

* Get rid of deref.

* Docs

* Use Self for instantiate_module

* REVERT ME

* Should be ok

* Commit

* Remove dbg

* Use fast-memory's erase

* Clean and undo hacks.

* Introduce a dedicated error for heap_base

* Ban the start function.

* Clean, docs and refactor

* Add rustflags.

* Update Cargo.lock

* Apply Basti's suggestions

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Rename allocates_huge_stack_array

* Extend TestClientBuilder with set_heap_pages

* Update the test.

* Update core/executor/src/wasm_executor.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Update core/executor/src/wasm_runtimes_cache.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Update core/executor/src/error.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Update core/executor/src/error.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Fix tests.

* Update cargo-lock

* Use wasmi master

* Use master wasmi

* Move tests.

* Use wasmi crates.io

* Update Cargo.lock

* Fix build.rs

* Bump runtime version

* Revert initial_heap_pages renaming

* Bump wasmi up to 0.5.0

* Bump runtime version

* Don't restore an instance every now and then

* Update core/executor/src/wasm_runtimes_cache.rs

Co-Authored-By: DemiMarie-parity <48690212+DemiMarie-parity@users.noreply.github.com>

* Propagate error in CacheError

* Clarify the get_heap_base call in instantiation

* Supply --export=__heap_base

See https://reviews.llvm.org/D62744

Co-authored-by: Jim Posen <jim.posen@gmail.com>

* Bump version.

* Use combinators for segments.

* Fix build.rs

* Fix build.rs for runtime-test

substrate/core/test-runtime/src/genesismap.rs

@@ -28,6 +28,7 @@ pub struct GenesisConfig {
 	pub changes_trie_config: Option<ChangesTrieConfiguration>,
 	pub authorities: Vec<AuthorityId>,
 	pub balances: Vec<(AccountId, u64)>,
+	pub heap_pages_override: Option<u64>,
 }
 
 impl GenesisConfig {
@@ -35,7 +36,8 @@ impl GenesisConfig {
 		support_changes_trie: bool,
 		authorities: Vec<AuthorityId>,
 		endowed_accounts: Vec<AccountId>,
-		balance: u64
+		balance: u64,
+		heap_pages_override: Option<u64>,
 	) -> Self {
 		GenesisConfig {
 			changes_trie_config: match support_changes_trie {
@@ -44,6 +46,7 @@ impl GenesisConfig {
 			},
 			authorities: authorities.clone(),
 			balances: endowed_accounts.into_iter().map(|a| (a, balance)).collect(),
+			heap_pages_override,
 		}
 	}
 
@@ -54,7 +57,10 @@ impl GenesisConfig {
 			.map(|(k, v)| (blake2_256(&k[..])[..].to_vec(), v.to_vec()))
 			.chain(vec![
 				(well_known_keys::CODE.into(), wasm_runtime),
-				(well_known_keys::HEAP_PAGES.into(), vec![].and(&(16 as u64))),
+				(
+					well_known_keys::HEAP_PAGES.into(),
+					vec![].and(&(self.heap_pages_override.unwrap_or(16 as u64))),
+				),
 			].into_iter())
 			.collect();
 		if let Some(ref changes_trie_config) = self.changes_trie_config {