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[SR-13383] Windows, Dispatch crashes after network request timeout #609

lxbndr opened this issue Aug 12, 2020 · 1 comment

[SR-13383] Windows, Dispatch crashes after network request timeout #609

lxbndr opened this issue Aug 12, 2020 · 1 comment


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@lxbndr lxbndr commented Aug 12, 2020

Previous ID SR-13383
Radar None
Original Reporter @lxbndr
Type Bug

Attachment: Download


Swift version 5.3-dev (LLVM 8cbcb68709, Swift df007a4f27)

Target: x86_64-unknown-windows-msvc

libdispatch and Foundation: swift-DEVELOPMENT-SNAPSHOT-2020-08-11-a,

Additional Detail from JIRA
Votes 0
Component/s Foundation, libdispatch
Labels Bug, Dispatch, Foundation, Windows
Assignee None
Priority Medium

md5: 49101804f13730f8eb31fad5750c4923

Issue Description:

Foundation uses CURL for processing network requests, and DispatchSource for listening to socket read/write availability events.

When network request from Foundation times out, DispatchSource is invalidated implicitly (by releasing and deallocating it).

libdispatch then performs cleanup for dispatch source in background thread. The cleanup includes disarming all pending events on a socket. But socket is already invalidated at that moment, and operation fails (WSAEventSelect returns error 10038 - WSAENOTSOCK).

Such error is considered fatal, and libdispatch intentionally crashes.

Sample code

import Foundation
import FoundationNetworking
import XCTest

class TestURLDataTask: XCTestCase {
    func test_timeout() {
        let config = URLSessionConfiguration.default
        config.timeoutIntervalForRequest = 8 // Value doesn't matter, 8 is just to wait less
        let session = URLSession(configuration: config, delegate: nil, delegateQueue: nil)
        let request = URLRequest(url: URL(string: "")!) // use any host that would time out

        let callbackCalled = expectation(description: "Task callback called")
        session.dataTask(with: request, completionHandler: { data, response, error in
        waitForExpectations(timeout: 10)
        Thread.sleep(forTimeInterval: 5)  // as Dispatch crashes asynchronously, give it some time

    static var allTests: [(String, (TestURLDataTask) -> () throws -> Void)] {
        return [("test_timeout", test_timeout),]


Crash location

The crash is in event_windows.c:222

Other dispatch sources

Other dispatch_source implementations (epoll, kevent) also has failable API calls in cleanup code, but intentionally ignore any errors.

It seems to me that socket cleanup have to be more indifferent to WSAEventSelect errors. Or we could ignore WSAENOTSOCK error at least.

Another solution would be somehow do dispatch source cleanup synchronously before socket invalidation in Foundation. Looks like this location in MultiHandle.swift would be a good place to do that. But I don't see any possibility to do it. Available Dispatch API would just mark Source as pending for asynchronous cleanup.

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@theblixguy theblixguy commented Aug 12, 2020

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
@shahmishal shahmishal transferred this issue from apple/swift May 5, 2022
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