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SONARPY-2914 Rule S7484: Events should be used instead of sleep in asynchronous loops (#273)
GitOrigin-RevId: b5c372d48e236888efdee408fdbb8d9bd6cf4943
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‎python-checks/src/main/java/org/sonar/python/checks/BusyWaitingInAsyncCheck.java‎

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/*
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* SonarQube Python Plugin
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* Copyright (C) 2011-2025 SonarSource SA
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* mailto:info AT sonarsource DOT com
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the Sonar Source-Available License Version 1, as published by SonarSource SA.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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* See the Sonar Source-Available License for more details.
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*
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* You should have received a copy of the Sonar Source-Available License
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* along with this program; if not, see https://sonarsource.com/license/ssal/
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*/
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package org.sonar.python.checks;
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import java.util.Optional;
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import javax.annotation.Nullable;
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import org.sonar.check.Rule;
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import org.sonar.plugins.python.api.PythonSubscriptionCheck;
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import org.sonar.plugins.python.api.SubscriptionContext;
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import org.sonar.plugins.python.api.symbols.Symbol;
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import org.sonar.plugins.python.api.symbols.Usage;
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import org.sonar.plugins.python.api.tree.AwaitExpression;
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import org.sonar.plugins.python.api.tree.BaseTreeVisitor;
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import org.sonar.plugins.python.api.tree.CallExpression;
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import org.sonar.plugins.python.api.tree.Expression;
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import org.sonar.plugins.python.api.tree.FileInput;
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import org.sonar.plugins.python.api.tree.FunctionDef;
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import org.sonar.plugins.python.api.tree.Name;
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import org.sonar.plugins.python.api.tree.Tree;
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import org.sonar.plugins.python.api.tree.Tree.Kind;
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import org.sonar.plugins.python.api.tree.WhileStatement;
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import org.sonar.python.tree.TreeUtils;
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import org.sonar.python.types.v2.TypeCheckMap;
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@Rule(key = "S7484")
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public class BusyWaitingInAsyncCheck extends PythonSubscriptionCheck {
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private static final String MESSAGE = "Refactor this loop to use an `Event` instead of polling with `sleep`.";
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private static final String SECONDARY_MESSAGE = "This function is async.";
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private static final String POLLING_MESSAGE = "Polling happens here.";
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private TypeCheckMap<Object> asyncSleepTypeChecks;
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@Override
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public void initialize(Context context) {
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context.registerSyntaxNodeConsumer(Kind.FILE_INPUT, this::initializeTypeCheckMap);
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context.registerSyntaxNodeConsumer(Kind.WHILE_STMT, this::checkWhileStatement);
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}
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private void initializeTypeCheckMap(SubscriptionContext ctx) {
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var object = new Object();
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asyncSleepTypeChecks = new TypeCheckMap<>();
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asyncSleepTypeChecks.put(ctx.typeChecker().typeCheckBuilder().isTypeOrInstanceWithName("asyncio.sleep"), object);
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asyncSleepTypeChecks.put(ctx.typeChecker().typeCheckBuilder().isTypeWithFqn("trio.sleep"), object);
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asyncSleepTypeChecks.put(ctx.typeChecker().typeCheckBuilder().isTypeOrInstanceWithName("anyio.sleep"), object);
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}
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private void checkWhileStatement(SubscriptionContext ctx) {
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var whileStmt = (WhileStatement) ctx.syntaxNode();
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var enclosingFuncDef = (FunctionDef) TreeUtils.firstAncestorOfKind(whileStmt, Kind.FUNCDEF);
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var asyncToken = Optional.ofNullable(enclosingFuncDef).map(FunctionDef::asyncKeyword);
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if (asyncToken.isEmpty()) {
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return;
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}
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var sleepFinder = new SleepCallFinder(asyncSleepTypeChecks);
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whileStmt.body().accept(sleepFinder);
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if (sleepFinder.sleepAwait == null) {
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return;
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}
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var conditionChecker = new GlobalOrNonLocalNameFinder(enclosingFuncDef);
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whileStmt.condition().accept(conditionChecker);
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if (conditionChecker.foundGlobalOrNonLocal) {
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ctx.addIssue(whileStmt.condition(), MESSAGE)
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.secondary(sleepFinder.sleepAwait, POLLING_MESSAGE)
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.secondary(asyncToken.get(), SECONDARY_MESSAGE);
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}
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}
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private static class GlobalOrNonLocalNameFinder extends BaseTreeVisitor {
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boolean foundGlobalOrNonLocal = false;
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private final FunctionDef whileLoopFunction;
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GlobalOrNonLocalNameFinder(FunctionDef whileLoopFunction) {
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this.whileLoopFunction = whileLoopFunction;
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}
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@Override
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public void visitName(Name name) {
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if (foundGlobalOrNonLocal) {
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return;
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}
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var symbol = name.symbol();
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if (symbol != null && isSymbolDeclaredInOuterScope(symbol, whileLoopFunction)) {
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foundGlobalOrNonLocal = true;
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}
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super.visitName(name);
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}
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// Use of Symbol V1 instead of SymbolV2 because of SONARPY-2974
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private static boolean isSymbolDeclaredInOuterScope(Symbol symbol, FunctionDef currentFunctionContext) {
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var fileInput = (FileInput) TreeUtils.firstAncestorOfKind(currentFunctionContext, Kind.FILE_INPUT);
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for (var usage : symbol.usages()) {
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if (usage.kind() == Usage.Kind.ASSIGNMENT_LHS) {
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if (fileInput.globalVariables().contains(symbol)) {
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return true;
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}
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var currentFunction = (FunctionDef) TreeUtils.firstAncestorOfKind(currentFunctionContext, Kind.FUNCDEF);
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while (currentFunction != null) {
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if (currentFunction.localVariables().contains(symbol)) {
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return true;
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}
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currentFunction = (FunctionDef) TreeUtils.firstAncestorOfKind(currentFunction, Kind.FUNCDEF);
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}
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}
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}
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return false;
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}
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}
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private static class SleepCallFinder extends BaseTreeVisitor {
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Tree sleepAwait = null;
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private final TypeCheckMap<Object> asyncSleepTypeChecks;
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SleepCallFinder(TypeCheckMap<Object> asyncSleepTypeChecks) {
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this.asyncSleepTypeChecks = asyncSleepTypeChecks;
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}
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@Override
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public void visitAwaitExpression(AwaitExpression awaitExpr) {
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var expr = awaitExpr.expression();
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if (expr instanceof CallExpression callExpr && isAsyncSleepCall(callExpr.callee())) {
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sleepAwait = awaitExpr.awaitToken();
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}
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super.visitAwaitExpression(awaitExpr);
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}
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@Override
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protected void scan(@Nullable Tree tree) {
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if (sleepAwait != null) {
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return;
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}
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super.scan(tree);
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}
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private boolean isAsyncSleepCall(Expression call) {
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return asyncSleepTypeChecks.getOptionalForType(call.typeV2()).isPresent();
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}
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}
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}

‎python-checks/src/main/java/org/sonar/python/checks/OpenSourceCheckList.java‎

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BreakContinueOutsideLoopCheck.class,
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BuiltinShadowingAssignmentCheck.class,
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BuiltinGenericsOverTypingModuleCheck.class,
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BusyWaitingInAsyncCheck.class,
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CancellationScopeNoCheckpointCheck.class,
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CaughtExceptionsCheck.class,
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ChangeMethodContractCheck.class,

‎python-checks/src/main/resources/org/sonar/l10n/py/rules/python/S7484.html‎

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<p>This rule raises an issue when the <code>sleep</code> function is used in an asynchronous loop instead of an Event object.</p>
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<h2>Why is this an issue?</h2>
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<p>Asynchronous tasks often need to wait for a condition to change or an event to occur. A simple-looking but inefficient way to achieve this is by
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polling the condition within a loop, using <code>sleep</code> to pause between checks:</p>
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<pre>
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while not condition_is_met:
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await asyncio.sleep(0.1) # Noncompliant
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# Condition is met, we can proceed
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</pre>
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<p>This busy-waiting approach is problematic in asynchronous code because it introduces increased latency. The task only notices the condition change
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after the <code>sleep</code> interval expires. If the condition becomes true just after the task starts sleeping, the reaction is delayed.</p>
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<p>Instead of polling with <code>sleep</code>, use dedicated synchronization primitives like <code>asyncio.Event</code>, <code>trio.Event</code> or
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<code>anyio.Event</code>. Using an <code>Event</code> allows a task to efficiently pause (<code>await event.wait()</code>) until another part of the
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program signals the event (<code>event.set()</code>). The waiting task consumes almost no resources while paused and reacts immediately when the event
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is set.</p>
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<h2>How to fix it in Asyncio</h2>
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<h3>Code examples</h3>
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<h4>Noncompliant code example</h4>
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<pre data-diff-id="2" data-diff-type="noncompliant">
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import asyncio
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SHARED_CONDITION = False
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async def worker():
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while not SHARED_CONDITION: # Noncompliant
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await asyncio.sleep(0.01)
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print("Condition is now true")
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asyncio.run(worker)
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</pre>
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<h4>Compliant solution</h4>
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<pre data-diff-id="2" data-diff-type="compliant">
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import asyncio
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SHARED_CONDITION = asyncio.Event()
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async def worker():
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await SHARED_CONDITION.wait() # Compliant
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print("Condition is now true")
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asyncio.run(worker)
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</pre>
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<h2>How to fix it in Trio</h2>
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<h3>Code examples</h3>
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<h4>Noncompliant code example</h4>
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<pre data-diff-id="1" data-diff-type="noncompliant">
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import trio
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SHARED_CONDITION = False
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async def worker():
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while not SHARED_CONDITION: # Noncompliant
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await trio.sleep(0.01)
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print("Condition is now true")
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trio.run(worker)
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</pre>
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<h4>Compliant solution</h4>
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<pre data-diff-id="1" data-diff-type="compliant">
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import trio
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SHARED_CONDITION = trio.Event()
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async def worker():
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await SHARED_CONDITION.wait() # Compliant
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print("Condition is now true")
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trio.run(worker)
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</pre>
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<h2>How to fix it in AnyIO</h2>
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<h3>Code examples</h3>
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<h4>Noncompliant code example</h4>
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<pre data-diff-id="3" data-diff-type="noncompliant">
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import anyio
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SHARED_CONDITION = False
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async def worker():
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while not SHARED_CONDITION: # Noncompliant
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await anyio.sleep(0.01)
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print("Condition is now true")
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anyio.run(worker)
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</pre>
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<h4>Compliant solution</h4>
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<pre data-diff-id="3" data-diff-type="compliant">
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import anyio
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SHARED_CONDITION = anyio.Event()
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async def worker():
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await SHARED_CONDITION.wait() # Compliant
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print("Condition is now true")
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anyio.run(worker)
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</pre>
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<h2>Resources</h2>
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<h3>Documentation</h3>
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<ul>
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<li> Asyncio documentation - <a href="https://docs.python.org/3/library/asyncio-sync.html#asyncio.Event">Event</a> </li>
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<li> Trio documentation - <a href="https://trio.readthedocs.io/en/stable/reference-core.html#broadcasting-an-event-with-event">Broadcasting an event
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with Event</a> </li>
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<li> AnyIO documentation - <a href="https://anyio.readthedocs.io/en/stable/synchronization.html#events">Events</a> </li>
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</ul>
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‎python-checks/src/main/resources/org/sonar/l10n/py/rules/python/S7484.json‎

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{
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"title": "Events should be used instead of `sleep` in asynchronous loops",
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"type": "CODE_SMELL",
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"status": "ready",
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"remediation": {
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"func": "Constant\/Issue",
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"constantCost": "10min"
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},
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"tags": [
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"async",
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"asyncio",
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"anyio",
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"trio"
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],
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"defaultSeverity": "Major",
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"ruleSpecification": "RSPEC-7484",
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"sqKey": "S7484",
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"scope": "All",
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"quickfix": "infeasible",
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"code": {
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"impacts": {
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"MAINTAINABILITY": "MEDIUM",
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"RELIABILITY": "MEDIUM"
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},
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"attribute": "EFFICIENT"
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}
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}

‎python-checks/src/main/resources/org/sonar/l10n/py/rules/python/Sonar_way_profile.json‎

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"S6984",
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"S6985",
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"S7483",
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"S7484",
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"S7486",
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"S7487",
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"S7488",

‎python-checks/src/test/java/org/sonar/python/checks/BusyWaitingInAsyncCheckTest.java‎

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/*
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* SonarQube Python Plugin
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* Copyright (C) 2011-2025 SonarSource SA
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* mailto:info AT sonarsource DOT com
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the Sonar Source-Available License Version 1, as published by SonarSource SA.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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* See the Sonar Source-Available License for more details.
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*
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* You should have received a copy of the Sonar Source-Available License
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* along with this program; if not, see https://sonarsource.com/license/ssal/
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*/
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package org.sonar.python.checks;
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import org.junit.jupiter.api.Test;
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import org.sonar.python.checks.utils.PythonCheckVerifier;
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class BusyWaitingInAsyncCheckTest {
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@Test
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void test() {
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PythonCheckVerifier.verify("src/test/resources/checks/busyWaitingInAsync.py", new BusyWaitingInAsyncCheck());
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}
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}

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