USE_PTHREADS=1 fails with LLVM ERROR: Cannot select ...

[chrisber]

After the latest merge of the pull request Initial support for pthreads with wasm #5710.
I was curious about thread support in webassembly and tried to compile the the following example cppreference storage duration , but compiling and executing with thread support only succeeded with asm as target.
Is thread support with the native webassembly backend currently limited or did I make a mistake?

emsdk sdk-incoming-64bit compiled from source (emscripten-core/emsdk@d3a5609)
emscripten/incoming (1754e32)
clang/fastcomp/src (emscripten-core/emscripten-fastcomp@7153769)
Firefox nightly Version 59.0a1

Example.cc:

#include <iostream>
#include <string>
#include <thread>
#include <mutex>
 
thread_local unsigned int rage = 1; 
std::mutex cout_mutex;
 
void increase_rage(const std::string& thread_name)
{
    ++rage; // modifying outside a lock is okay; this is a thread-local variable
    std::lock_guard<std::mutex> lock(cout_mutex);
    std::cout << "Rage counter for " << thread_name << ": " << rage << '\n';
}
 
int main()
{
    std::thread a(increase_rage, "a"), b(increase_rage, "b");
 
    {
        std::lock_guard<std::mutex> lock(cout_mutex);
        std::cout << "Rage counter for main: " << rage << '\n';
    }
 
    a.join();
    b.join();
}

Build from source for asm :

 git clone https://github.com/juj/emsdk.git
 cd emsdk
./emsdk install sdk-incoming-64bit binaryen-master-64bit
./emsdk activate sdk-incoming-64bit binaryen-master-64bit
. ./emsdk_env.sh
emcc -v -std=c++11  -01 \
-s USE_PTHREADS=1 \
-s PROXY_TO_PTHREAD=1 \
-s VERBOSE=1 \
example.cc -o example.html

Compiles and runs successfull when optimization is set to-01 or above (fails with -O0).

Program output:

Preallocating 1 workers for a pthread spawn pool.
Preallocating 1 workers for a pthread spawn pool.
Preallocating 1 workers for a pthread spawn pool.
Rage counter for main: 1
Rage counter for a: 2
Rage counter for b: 3

Build from source with asm2wasm backend:

 git clone https://github.com/juj/emsdk.git
 cd emsdk
 ./emsdk install sdk-incoming-64bit binaryen-master-64bit
 ./emsdk activate sdk-incoming-64bit binaryen-master-64bit
 . ./emsdk_env.sh
 DEBUG=1 emcc -v -std=c++11   \
-s USE_PTHREADS=1 \
-s PROXY_TO_PTHREAD=1 \
-s WASM=1 \
-s VERBOSE=1 \
example.cc -o example.html

Compiles but the program is not executable.

Build from source with native wasm backend:

 git clone https://github.com/juj/emsdk.git
 cd emsdk
./emsdk install --enable-wasm sdk-incoming-64bit binaryen-master-64bit
./emsdk activate --enable-wasm sdk-incoming-64bit binaryen-master-64bit
. ./emsdk_env.sh
DEBUG=1 EMCC_WASM_BACKEND=1 emcc -v -std=c++11   \
-s USE_PTHREADS=1 \
-s PROXY_TO_PTHREAD=1 \
-s WASM=1 \
-s VERBOSE=1 \
example.cc -o example.html

Compilation fails with error:

LLVM ERROR: Cannot select: 0x55d8f3285d00: i32 = GlobalTLSAddress<i32* @rage> 0 In function: _ZTW4rage

It seems like an issue with the statement thread_local unsigned int rage = 1;

[juj]

The missing piece here is the thread_local keyword, which is not yet supported in our multithreading work. This is on the TODO list though, since it's quite an important one. Thanks for the test case!

[trailcode]

I am having the same problem. If I compile with -s WASM=1 it does not work.

[stale]

This issue has been automatically marked as stale because there has been no activity in the past year. It will be closed automatically if no further activity occurs in the next 7 days. Feel free to re-open at any time if this issue is still relevant.

[tlively]

Actually, this should be fixed now that we support thread_locals.