Fix a crash in FAISS benchmark wrapper introduced in #2021 (#2062)

With the changes introduced by #2021, the copied FAISS benchmark wrapper contains a cuda event that is used for synchronizing between streams during search. The lifetime of the event is the same as of the wrapper, but the event handle itself is copied between the wrappers; this leads to illegal memory accesses and crashes.
This PR fixes the bug by creating a new cuda event on each wrapper copy, so that the wrappers do not share their synchronization events.

Authors:
  - Artem M. Chirkin (https://github.com/achirkin)

Approvers:
  - Corey J. Nolet (https://github.com/cjnolet)

URL: #2062

cpp/bench/ann/src/faiss/faiss_gpu_wrapper.h

@@ -80,6 +80,19 @@ class OmpSingleThreadScope {
 
 namespace raft::bench::ann {
 
+struct copyable_event {
+  copyable_event() { RAFT_CUDA_TRY(cudaEventCreate(&value_, cudaEventDisableTiming)); }
+  ~copyable_event() { RAFT_CUDA_TRY_NO_THROW(cudaEventDestroy(value_)); }
+  copyable_event(copyable_event&&)            = default;
+  copyable_event& operator=(copyable_event&&) = default;
+  copyable_event(const copyable_event& res) : copyable_event{} {}
+  copyable_event& operator=(const copyable_event& other) = delete;
+  operator cudaEvent_t() const noexcept { return value_; }
+
+ private:
+  cudaEvent_t value_{nullptr};
+};
+
 template <typename T>
 class FaissGpu : public ANN<T> {
  public:
@@ -97,18 +110,15 @@ class FaissGpu : public ANN<T> {
 
   FaissGpu(Metric metric, int dim, const BuildParam& param)
     : ANN<T>(metric, dim),
+      gpu_resource_{std::make_shared<faiss::gpu::StandardGpuResources>()},
       metric_type_(parse_metric_type(metric)),
       nlist_{param.nlist},
       training_sample_fraction_{1.0 / double(param.ratio)}
   {
     static_assert(std::is_same_v<T, float>, "faiss support only float type");
     RAFT_CUDA_TRY(cudaGetDevice(&device_));
-    RAFT_CUDA_TRY(cudaEventCreate(&sync_, cudaEventDisableTiming));
-    faiss_default_stream_ = gpu_resource_.getDefaultStream(device_);
   }
 
-  virtual ~FaissGpu() noexcept { RAFT_CUDA_TRY_NO_THROW(cudaEventDestroy(sync_)); }
-
   void build(const T* dataset, size_t nrow, cudaStream_t stream = 0) final;
 
   virtual void set_search_param(const FaissGpu<T>::AnnSearchParam& param) {}
@@ -142,7 +152,7 @@ class FaissGpu : public ANN<T> {
 
   void stream_wait(cudaStream_t stream) const
   {
-    RAFT_CUDA_TRY(cudaEventRecord(sync_, faiss_default_stream_));
+    RAFT_CUDA_TRY(cudaEventRecord(sync_, gpu_resource_->getDefaultStream(device_)));
     RAFT_CUDA_TRY(cudaStreamWaitEvent(stream, sync_));
   }
 
@@ -162,14 +172,13 @@ class FaissGpu : public ANN<T> {
    * faiss::gpu::StandardGpuResources are thread-safe.
    *
    */
-  mutable faiss::gpu::StandardGpuResources gpu_resource_;
+  mutable std::shared_ptr<faiss::gpu::StandardGpuResources> gpu_resource_;
   std::shared_ptr<faiss::gpu::GpuIndex> index_;
   std::shared_ptr<faiss::IndexRefineFlat> index_refine_{nullptr};
   faiss::MetricType metric_type_;
   int nlist_;
   int device_;
-  cudaEvent_t sync_{nullptr};
-  cudaStream_t faiss_default_stream_{nullptr};
+  copyable_event sync_{};
   double training_sample_fraction_;
   std::shared_ptr<faiss::SearchParameters> search_params_;
   const T* dataset_;
@@ -278,7 +287,7 @@ class FaissGpuIVFFlat : public FaissGpu<T> {
     faiss::gpu::GpuIndexIVFFlatConfig config;
     config.device = this->device_;
     this->index_  = std::make_shared<faiss::gpu::GpuIndexIVFFlat>(
-      &(this->gpu_resource_), dim, param.nlist, this->metric_type_, config);
+      this->gpu_resource_.get(), dim, param.nlist, this->metric_type_, config);
   }
 
   void set_search_param(const typename FaissGpu<T>::AnnSearchParam& param) override
@@ -321,7 +330,7 @@ class FaissGpuIVFPQ : public FaissGpu<T> {
     config.device                 = this->device_;
 
     this->index_ =
-      std::make_shared<faiss::gpu::GpuIndexIVFPQ>(&(this->gpu_resource_),
+      std::make_shared<faiss::gpu::GpuIndexIVFPQ>(this->gpu_resource_.get(),
                                                   dim,
                                                   param.nlist,
                                                   param.M,
@@ -383,7 +392,7 @@ class FaissGpuIVFSQ : public FaissGpu<T> {
     faiss::gpu::GpuIndexIVFScalarQuantizerConfig config;
     config.device = this->device_;
     this->index_  = std::make_shared<faiss::gpu::GpuIndexIVFScalarQuantizer>(
-      &(this->gpu_resource_), dim, param.nlist, qtype, this->metric_type_, true, config);
+      this->gpu_resource_.get(), dim, param.nlist, qtype, this->metric_type_, true, config);
   }
 
   void set_search_param(const typename FaissGpu<T>::AnnSearchParam& param) override
@@ -426,7 +435,7 @@ class FaissGpuFlat : public FaissGpu<T> {
     faiss::gpu::GpuIndexFlatConfig config;
     config.device = this->device_;
     this->index_  = std::make_shared<faiss::gpu::GpuIndexFlat>(
-      &(this->gpu_resource_), dim, this->metric_type_, config);
+      this->gpu_resource_.get(), dim, this->metric_type_, config);
   }
   void set_search_param(const typename FaissGpu<T>::AnnSearchParam& param) override
   {