llama-context : sync pending async copies before clearing embd_seq (#25676)

src/llama-context.cpp

@@ -474,6 +474,9 @@ llama_context::llama_context(
 }
 
 llama_context::~llama_context() {
+    // wait for any pending asynchronous copies into the output buffers before they are freed
+    synchronize();
+
     if (!model.hparams.no_alloc) {
         for (size_t i = 0; i < backend_ptrs.size(); ++i) {
             ggml_backend_t             backend = backend_ptrs[i];
@@ -1417,13 +1420,17 @@ int llama_context::encode(const llama_batch & batch_inp) {
     // micro-batching is not possible for non-causal encoding, so we process the batch in a single shot
     GGML_ASSERT(cparams.n_ubatch >= n_tokens && "encoder requires n_ubatch >= n_tokens");
 
+    // TODO: this clear of the buffer can easily be forgotten - need something better
+    // sync first so any in-flight async copies into embd_seq complete before it is freed
+    if (!embd_seq.empty()) {
+        synchronize();
+    }
+    embd_seq.clear();
+
     if (t_compute_start_us == 0) {
         t_compute_start_us = ggml_time_us();
     }
 
-    // TODO: this clear of the buffer can easily be forgotten - need something better
-    embd_seq.clear();
-
     sched_reserve();
 
     n_queued_tokens += n_tokens;
@@ -1762,13 +1769,18 @@ int llama_context::decode(const llama_batch & batch_inp) {
 
     GGML_ASSERT((cparams.causal_attn || cparams.n_ubatch >= n_tokens_all) && "non-causal attention requires n_ubatch >= n_tokens");
 
+    // TODO: this clear of the buffer can easily be forgotten - need something better
+    // sync first so any in-flight async copies into embd_seq complete before it is freed
+    if (!embd_seq.empty()) {
+        synchronize();
+    }
+    embd_seq.clear();
+
     if (t_compute_start_us == 0) {
         t_compute_start_us = ggml_time_us();
     }
     n_queued_tokens += n_tokens_all;
 
-    // TODO: this clear of the buffer can easily be forgotten - need something better
-    embd_seq.clear();
     output_swaps.clear();
 
     sched_reserve();