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Fences must exit #1940

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Fences must exit #1940

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3ad9031
fences must exit
awni Mar 7, 2025
127de88
Fix the sig_handler check
angeloskath Mar 8, 2025
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30 changes: 29 additions & 1 deletion mlx/backend/metal/fence.cpp
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Original file line number Diff line number Diff line change
@@ -1,12 +1,39 @@
// Copyright © 2024 Apple Inc.
#include "mlx/fence.h"
#include <csignal>

#include "mlx/backend/metal/device.h"
#include "mlx/backend/metal/metal_impl.h"
#include "mlx/fence.h"
#include "mlx/scheduler.h"
#include "mlx/utils.h"

namespace mlx::core {

void signal_handler(int signum);

MTL::Buffer* signal_buffer() {
auto init = []() {
signal(SIGTERM, signal_handler);
auto dtor = [](void* buf) {
allocator::free(static_cast<MTL::Buffer*>(buf));
};
auto buf = std::shared_ptr<void>(
allocator::malloc_or_wait(sizeof(uint32_t)).ptr(), dtor);
static_cast<uint32_t*>(
static_cast<MTL::Buffer*>(buf.get())->contents())[0] = 0;
return buf;
};
static std::shared_ptr<void> buf = init();
return static_cast<MTL::Buffer*>(buf.get());
}

void signal_handler(int signum) {
auto buf = signal_buffer();
static_cast<std::atomic_uint*>(buf->contents())[0] = 1;
signal(signum, SIG_DFL);
raise(signum);
}

struct FenceImpl {
FenceImpl() {
auto d = metal::device(Device::gpu).mtl_device();
Expand Down Expand Up @@ -94,6 +121,7 @@ void Fence::wait(Stream stream, const array& x) {
auto buf = static_cast<MTL::Buffer*>(f.fence);
compute_encoder.set_buffer(buf, 0);
compute_encoder.set_bytes(f.count, 1);
compute_encoder.set_buffer(signal_buffer(), 2);
compute_encoder.dispatch_threads(kernel_dims, kernel_dims);

d.get_command_buffer(idx)->addCompletedHandler(
Expand Down
5 changes: 3 additions & 2 deletions mlx/backend/metal/kernels/fence.metal
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Original file line number Diff line number Diff line change
Expand Up @@ -39,13 +39,14 @@ constexpr constant metal::thread_scope thread_scope_system =
// single thread kernel to spin wait for timestamp value
[[kernel]] void fence_wait(
volatile coherent(system) device uint* timestamp [[buffer(0)]],
constant uint& value [[buffer(1)]]) {
constant uint& value [[buffer(1)]],
volatile coherent(system) device uint* sig_handler [[buffer(2)]]) {
while (1) {
metal::atomic_thread_fence(
metal::mem_flags::mem_device,
metal::memory_order_seq_cst,
metal::thread_scope_system);
if (timestamp[0] >= value) {
if (timestamp[0] >= value || sig_handler[0] > 0) {
break;
}
}
Expand Down