Use Asyncify to process ties in web UI

.gitignore

@@ -1,3 +1,3 @@
 /target
 /html/opentally.js
-/html/opentally_bg.wasm
+/html/opentally_*.wasm

build_wasm.sh

@@ -1,3 +1,19 @@
 #!/bin/sh
+PATH=$PATH:$HOME/.cargo/bin
+
+# Build cargo
 PROFILE=${1:-release}
-cargo build --lib --target wasm32-unknown-unknown --$PROFILE && /home/runassudo/.cargo/bin/wasm-bindgen --target no-modules target/wasm32-unknown-unknown/$PROFILE/opentally.wasm --out-dir html --no-typescript
+if [ $PROFILE == 'debug' ]; then
+	cargo build --lib --target wasm32-unknown-unknown
+else
+	cargo build --lib --target wasm32-unknown-unknown --$PROFILE
+fi
+
+# Apply wasm-bindgen
+wasm-bindgen --target no-modules target/wasm32-unknown-unknown/$PROFILE/opentally.wasm --out-dir html --no-typescript
+
+# Apply Asyncify
+MANGLED=$(wasm-dis html/opentally_bg.wasm | grep '(import "wbg" "__wbg_getuserinput_' | awk '{print $3;}' | tr -d '"')
+wasm-opt -O2 --asyncify --pass-arg asyncify-imports@wbg.$MANGLED html/opentally_bg.wasm -o html/opentally_async.wasm
+
+rm html/opentally_bg.wasm

html/index.html

@@ -295,7 +295,6 @@
 		<div id="printWarning">Printing directly from this page is not supported. Use the ‘Print result’ button to generate a printer-friendly report.</div>
 		
 		<script src="vendor/vanilla-js-dropdown.min.js"></script>
-		<script src="opentally.js?v=GITVERSION"></script>
 		<script src="index.js?v=GITVERSION"></script>
 	</body>
 </html>

html/worker.js

@@ -1,9 +1,18 @@
 importScripts('opentally.js');
 
 var wasm = wasm_bindgen;
+var wasmRaw;
+
+// For asyncify
+const DATA_ADDR = 16;
+const DATA_START = DATA_ADDR + 8;
+const DATA_END = 50 * 1024; // Needs to be increased compared with Asyncify default
 
 async function initWasm() {
-	await wasm_bindgen('opentally_bg.wasm');
+	wasmRaw = await wasm_bindgen('opentally_async.wasm');
+	
+	new Int32Array(wasmRaw.memory.buffer, DATA_ADDR).set([DATA_START, DATA_END]);
+	
 	postMessage({'type': 'init', 'version': wasm.version()});
 }
 initWasm();
@@ -59,27 +68,30 @@ onmessage = function(evt) {
 		
 		stageNum = 2;
 		
-		resume_count();
+		resumeCount();
 		
 	} else if (evt.data.type == 'userInput') {
-		user_input_buffer = evt.data.response;
-		resume_count();
+		userInputBuffer = evt.data.response;
+		
+		// Rewind the stack
+		// Asyncify will retrace the function calls in the stack until again reaching get_user_input
+		wasmRaw.asyncify_start_rewind(DATA_ADDR);
+		resumeCount();
 	}
 }
 
-function resume_count() {
+function resumeCount() {
 	for (;; stageNum++) {
-		try {
-			let isDone = wasm['count_one_stage_' + numbers](state, opts);
-			if (isDone) {
-				break;
-			}
-		} catch (ex) {
-			if (ex === "RequireInput") {
-				return;
-			} else {
-				throw ex;
-			}
+		let isDone = wasm['count_one_stage_' + numbers](state, opts);
+		
+		if (unwindingStack) {
+			// This stage caused a stack unwind in get_user_input so ignore the result
+			// We will resume execution when a userInput message is received
+			return;
+		}
+		
+		if (isDone) {
+			break;
 		}
 		
 		postMessage({'type': 'updateResultsTable', 'result': wasm['update_results_table_' + numbers](stageNum, state, opts)});
@@ -90,15 +102,27 @@ function resume_count() {
 	postMessage({'type': 'finalResultSummary', 'summary': wasm['final_result_summary_' + numbers](state, opts)});
 }
 
-var user_input_buffer = null;
+var unwindingStack = false;
+var userInputBuffer = null;
 
-function read_user_input_buffer(message) {
-	if (user_input_buffer === null) {
+function get_user_input(message) {
+	if (userInputBuffer === null) {
 		postMessage({'type': 'requireInput', 'message': message});
+		
+		// Record the current state of the stack
+		wasmRaw.asyncify_start_unwind(DATA_ADDR);
+		unwindingStack = true;
+		
+		// No further WebAssembly will be executed and control will return to resumeCount
 		return null;
 	} else {
-		let user_input = user_input_buffer;
-		user_input_buffer = null;
-		return user_input;
+		// We have reached the point the stack was originally unwound, so resume normal execution
+		unwindingStack = false;
+		wasmRaw.asyncify_stop_rewind();
+		
+		// Return the correct result to WebAssembly
+		let userInput = userInputBuffer;
+		userInputBuffer = null;
+		return userInput;
 	}
 }

src/ties.rs

@@ -198,7 +198,6 @@ where
 }
 
 /// Prompt the candidate for input, depending on CLI or WebAssembly target
-// FIXME: This may have unexpected behaviour if the tie occurs in the middle of a stage
 #[cfg(not(target_arch = "wasm32"))]
 fn prompt<'c>(candidates: &Vec<&'c Candidate>) -> Result<&'c Candidate, STVError> {
 	println!("Multiple tied candidates:");
@@ -231,7 +230,7 @@ fn prompt<'c>(candidates: &Vec<&'c Candidate>) -> Result<&'c Candidate, STVError
 #[cfg(target_arch = "wasm32")]
 #[wasm_bindgen]
 extern "C" {
-	fn read_user_input_buffer(s: &str) -> Option<String>;
+	fn get_user_input(s: &str) -> Option<String>;
 }
 
 #[cfg(target_arch = "wasm32")]
@@ -242,25 +241,30 @@ fn prompt<'c>(candidates: &Vec<&'c Candidate>) -> Result<&'c Candidate, STVError
 	}
 	message.push_str(&format!("Which candidate to select? [1-{}] ", candidates.len()));
 	
-	match read_user_input_buffer(&message) {
-		Some(response) => {
-			match response.trim().parse::<usize>() {
-				Ok(val) => {
-					if val >= 1 && val <= candidates.len() {
-						return Ok(candidates[val - 1]);
-					} else {
-						let _ = read_user_input_buffer(&message);
-						return Err(STVError::RequireInput);
+	loop {
+		let response = get_user_input(&message);
+		
+		match response {
+			Some(response) => {
+				match response.trim().parse::<usize>() {
+					Ok(val) => {
+						if val >= 1 && val <= candidates.len() {
+							return Ok(candidates[val - 1]);
+						} else {
+							// Invalid selection
+							continue;
+						}
+					}
+					Err(_) => {
+						// Invalid selection
+						continue;
 					}
 				}
-				Err(_) => {
-					let _ = read_user_input_buffer(&message);
-					return Err(STVError::RequireInput);
-				}
 			}
-		}
-		None => {
-			return Err(STVError::RequireInput);
+			None => {
+				// No available user input in buffer - stack will be unwound
+				unreachable!();
+			}
 		}
 	}
 }