Open
Description
openedon Aug 19, 2024
Reduced from JuliaGPU/CUDA.jl#2449 filed by @miniskar:
- create a pthread on which we call back into Julia and
runa command - have the main thread block on
pthread_join - the foreign thread cannot make progress because of some lock being held
#include <julia.h>
#include <pthread.h>
typedef void (*julia_callback)();
void *thread_function(void* callback) {
printf("Calling Julia from thread\n");
((julia_callback)callback)();
return NULL;
}
void call_on_thread(julia_callback callback) {
printf("Creating thread\n");
pthread_t thread;
pthread_create(&thread, NULL, thread_function, callback);
pthread_join(thread, NULL);
}
// alternative version that doesn't use a foreign thread,
// and as a result doesn't deadlock
void call_directly(julia_callback callback) {
printf("Calling Julia directly\n");
callback();
}function callback()::Cvoid
println("Running a command")
run(`echo 42`)
return
end
function main()
callback_ptr = @cfunction(callback, Cvoid, ())
gc_state = @ccall(jl_gc_safe_enter()::Int8)
ccall((:call_on_thread, "./wip.so"), Cvoid, (Ptr{Cvoid},), callback_ptr)
@ccall(jl_gc_safe_leave(gc_state::Int8)::Cvoid)
println("Done")
end
main()❯ gcc -fPIC -shared -o wip.so wip.c -isystem $JULIA/include/julia -isystem /opt/cuda/include -L$JULIA/lib -ljulia -lpthread && \
julia --project wip.jl
Creating thread
Calling Julia from thread
Running a command^C
[41055] signal 2: Interrupt
in expression starting at /home/tim/Julia/pkg/CUDA/wip.jl:16
unknown function (ip: 0x7b4dd01ada17)
pthread_cond_wait at /usr/lib/libc.so.6 (unknown line)
uv_cond_wait at /workspace/srcdir/libuv/src/unix/thread.c:822
ijl_task_get_next at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-11/src/scheduler.c:584
poptask at ./task.jl:1012
wait at ./task.jl:1021
uv_write at ./stream.jl:1072
unsafe_write at ./stream.jl:1145
write at ./strings/io.jl:248 [inlined]
print at ./strings/io.jl:250 [inlined]
print at ./strings/io.jl:46
jl_apply at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-11/src/julia.h:2156 [inlined]
do_apply at /cache/build/builder-amdci4-0/julialang/julia-release-1-dot-11/src/builtins.c:831
println at ./strings/io.jl:75
println at ./coreio.jl:4
callback at /home/tim/Julia/pkg/CUDA/wip.jl:3
I wasn't even sure if this is guaranteed to work, but @vchuravy mentioned that marking the blocking ccall @gc_safe ought to be enough to not have Julia hold any locks when entering C, so filing this as an issue here.
cc @vtjnash
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment