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

skelly-energid · 2023-10-17T23:23:39Z

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().

The text was updated successfully, but these errors were encountered:

sbc100 · 2023-10-26T19:10:49Z

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 · 2023-10-27T14:18:44Z

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 · 2023-10-27T15:48:45Z

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 · 2023-10-27T16:38:55Z

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

sbc100 · 2023-10-27T16:51:39Z

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 mentioned this issue Feb 8, 2024

[emval] Move lifecycle mangement from JS to C++. #21300

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

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

skelly-energid commented Oct 17, 2023

sbc100 commented Oct 26, 2023

skelly-energid commented Oct 27, 2023 •

edited

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sbc100 commented Oct 27, 2023

skelly-energid commented Oct 27, 2023 •

edited

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sbc100 commented Oct 27, 2023

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

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

Comments

skelly-energid commented Oct 17, 2023

sbc100 commented Oct 26, 2023

skelly-energid commented Oct 27, 2023 • edited Loading

sbc100 commented Oct 27, 2023

skelly-energid commented Oct 27, 2023 • edited Loading

sbc100 commented Oct 27, 2023

skelly-energid commented Oct 27, 2023 •

edited

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skelly-energid commented Oct 27, 2023 •

edited

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