[UR][L0] Free the active-barrier wait list when all barrier events have completed

[uditagarwal97]

ur_queue_handle_t_::insertActiveBarriers() builds a ur_ze_event_list_t from the
queue's active barriers and then, if the resulting length is zero, returns early:

    if (ActiveBarriersWaitList.Length == 0) {
      return UR_RESULT_SUCCESS;
    }

createAndRetainUrZeEventList() allocates its ZeEventList and UrEventList arrays up
front, before filtering, so a zero length does not mean nothing was allocated - it
means every barrier event had already completed by the time the list was built.
ur_ze_event_list_t has no destructor, and the only thing that frees those arrays is
the ownership transfer further down the function, which this early return skips.
So both arrays leak, every time.

Found by LeakSanitizer on level_zero:gpu.

Reproduction

#include <sycl/detail/core.hpp>
#include <vector>

int main() {
  sycl::queue Q;
  std::vector<int> Data(1024, 0);
  sycl::buffer<int> Buf(Data.data(), sycl::range<1>(1024));
  Q.submit([&](sycl::handler &CGH) {
    auto Acc = Buf.get_access<sycl::access_mode::write>(CGH);
    CGH.parallel_for(sycl::range<1>(1024), [=](sycl::id<1> I) { Acc[I] = 5; });
  });
  Q.ext_oneapi_submit_barrier().wait();
  auto HostAcc = Buf.get_host_access();
  return HostAcc[0] == 5 ? 0 : 1;
}

The .wait() is what makes it fire: the barrier event is complete by the time the host-accessor
read-back asks for a command list, so the wait list comes back with Length == 0.

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Co-Authored-By: Claude Opus 5 (1M context) noreply@anthropic.com

[Copilot]

🟢 Approval recommended

The cleanup correctly releases both allocated arrays without affecting retained events or control flow.

Pull request overview

Fixes a Level Zero queue memory leak when all active barrier events have completed.

Changes:

• Frees allocated wait-list arrays before the zero-length early return.
• Documents why cleanup remains necessary for an empty filtered list.

File summaries

File	Description
unified-runtime/source/adapters/level_zero/queue.cpp	Cleans up empty active-barrier wait lists.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Balanced

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