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skelly-energid opened this issue Oct 17, 2023 · 8 comments
Open

Namespace-level thread can cause other threads to not start sometimes #20477

skelly-energid opened this issue Oct 17, 2023 · 8 comments

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@skelly-energid
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Version of emscripten/emsdk:

 3.1.46

Failing command line in full:

The script will build and run the page, refreshing until the thread fails to start for some time. Due to the namespace-level object, it is random whether runThread() runs successfully. When it breaks, it seems to deadlock when attempting to execute the cout line.

#!/bin/sh

set -e
set -v

cat << EOF > mywrapper.cpp

#include <atomic>
#include <memory>
#include <thread>

class MyWrapper
{
public:
    explicit MyWrapper();
    ~MyWrapper();
    bool isThreadReady() const;

private:
    void runThread();

    std::unique_ptr<std::thread> m_ThreadPtr;

    std::atomic_bool m_IsThreadReady;
};

#include <emscripten/bind.h>

#include <iostream>

struct StaticInitStruct
{
  StaticInitStruct() : m_thread_id(0)
  {
    pthread_attr_t attr;
    pthread_attr_init(&attr);
    pthread_attr_setstacksize(&attr, 1024 * 1024);

    const int thread_created = pthread_create(&m_thread_id, &attr, _start, this);
    pthread_attr_destroy(&attr);

  }

  static void* _start(void* context)
  {
    std::cout << "STARTED\n";
    return nullptr;
  }

  pthread_t m_thread_id;
};

int i1;
std::string s1;
std::string s2;
int i2;
std::string s3;
std::string s4;
unsigned int s5;
StaticInitStruct statInit;

int main(int argc, char** argv)
{
    return 0;
}

MyWrapper::MyWrapper() :
    m_IsThreadReady(false)
{
    m_ThreadPtr.reset(
        new std::thread(&MyWrapper::runThread, this));
}

MyWrapper::~MyWrapper()
{
    if (m_ThreadPtr)
    {
        m_ThreadPtr->join();
        m_ThreadPtr.reset();
    }
}

void MyWrapper::runThread()
{
    std::cout << "runThread\n";

    m_IsThreadReady.store(true);
}


bool MyWrapper::isThreadReady() const
{
    return m_IsThreadReady.load();
}

// clang-format off
EMSCRIPTEN_BINDINGS(my_wrapper)
{
    emscripten::class_<MyWrapper>("MyWrapper")
        .constructor()
        .function("isThreadReady", &MyWrapper::isThreadReady)
        ;
}
// clang-format on
EOF

cat << EOF > index.html
<head>

    <script type='text/javascript' src=./myWrapperModule.js />
</head>

<body>
  <script>

    console.log("Get started");
</script>

  <script>

    MyWrapperModule().then(module => {
        var wrapper = new module.MyWrapper();

        var refreshPageNow = false;

        setTimeout(() => {
            refreshPageNow = true;
        }, 1750);

        var threadCheckInterval = setInterval(() => {
            if (wrapper.isThreadReady())
            {
                console.trace("READY");
                clearInterval(threadCheckInterval);
                location.reload();
            } else if (refreshPageNow) {
                console.log("BROKEN");
                clearInterval(threadCheckInterval);
                document.getElementById("result").innerHTML = "BROKEN";
            } else {
                console.log("WAIT");
            }
        }, 500);
    });
  </script>

    <p>TESTING</p>
    <p id="result"></p>
</body>
EOF

cat << EOF > pre.js
Module['mainScriptUrlOrBlob'] = self.location.origin + '/myWrapperModule.js';
EOF

em++ -sUSE_PTHREADS -fwasm-exceptions  -O2 -g -o mywrapper.cpp.o -c mywrapper.cpp
em++ -sUSE_PTHREADS -fwasm-exceptions  -O2 -g -sWASM=1 \
        -sPROXY_TO_PTHREAD -sINITIAL_MEMORY=128MB -sPTHREAD_POOL_SIZE=1 -sMODULARIZE=1 \
        -sEXPORT_NAME=MyWrapperModule --pre-js=pre.js --minify=0 --bind \
        -sENVIRONMENT=web,worker mywrapper.cpp.o -o myWrapperModule.js

emrun index.html

This likely can't be made to work, so it should maybe be documented, diagnosed and possibly fail-early if pthread_create is called before main().
@sbc100
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sbc100 commented Oct 26, 2023

I don't see any reason why pthread_create wouldn't work in a static constructor (i.e. before main) . That should work fine.

@skelly-energid
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skelly-energid commented Oct 27, 2023 •
edited
Loading

I don't see any reason why pthread_create wouldn't work in a static constructor (i.e. before main) . That should work fine.

Ok, then ignore my speculating :). The testcase fails nevertheless.

@sbc100
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sbc100 commented Oct 27, 2023

Anything you can do to narrow down the test case would be great. For example, can you remove the StaticInitStruct completely now?

Can s1 - s5 removed? Can i1 and i2 be removed?

Can main be removed?

@skelly-energid
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skelly-energid commented Oct 27, 2023 •
edited
Loading

As a sanity check - can you try my repro and confirm you can reproduce the issue?

@sbc100
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sbc100 commented Oct 27, 2023

I don't think I'll have time to look at this today, but maybe next week. The smaller you can make the repro the easier it will be for whoever does look at it.

@mrolig5267319 mrolig5267319 mentioned this issue Feb 8, 2024
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@skelly-energid
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This still fails with emscripten sdk 3.1.69.

Can you run the testcase? Then you can remove any lines you like.

@sbc100
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sbc100 commented Nov 20, 2024

I tried to reproduce using the script above and that page seems to keep reloading just fine and doesn't reach "BROKEN". I tried both with and without devtools enabled.

How many times does it normally take to fail for you? What browser are you using? Can you try the very latest version 3.1.72?

@skelly-energid
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I've reproduced it with 3.1.72.

I'm using "Chromium Version 131.0.6778.85 (Official Build) snap (64-bit)" on Ubuntu 24.04.1 LTS.

It takes about 30 seconds until the Broken message comes up.

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@sbc100 @skelly-energid