add endpoint /v1/cancel

README.md

@@ -364,6 +364,16 @@ Not yet. Now prima.cpp supports only CUDA-based GPUs. Vulkan is in our roadmap,
 
 No worries, this is expected. Prima.cpp found that this device was too slow, and dropping it could speed up inference, so it was removed.
 
+**8. How to cancel a running task?**
+
+Besides closing the HTTP/SSE connection, prima.cpp offers a handy `/v1/cancel` endpoint to cancel a running task by its `task_id`.
+
+```shell
+curl -X POST http://localhost:8080/v1/cancel \
+     -H "Content-Type: application/json" \
+     -d '{"task_id": 0}'
+```
+
 ## ❤️ Acknowledgment
 This project builds upon the incredible work from the open-source community, especially [ggml, gguf](https://github.com/ggml-org/ggml), and [llama.cpp](https://github.com/ggml-org/llama.cpp). We gratefully acknowledge their contributions.
 

examples/server/server.cpp

@@ -1532,11 +1532,22 @@ struct server_context {
         cancel_tasks.reserve(id_tasks.size());
         for (const auto & id_task : id_tasks) {
             SRV_WRN("cancel task, id_task = %d\n", id_task);
-
+            
+            // create a cancel task for id_task
             server_task task;
             task.type      = SERVER_TASK_TYPE_CANCEL;
             task.id_target = id_task;
             cancel_tasks.push_back(task);
+
+            // notify the results queue that the task is cancelled
+            server_task_result cancel_res;
+            cancel_res.id    = id_task;
+            cancel_res.stop  = true;      
+            cancel_res.error = false;     
+            cancel_res.data  = {{"cancelled", true}};
+            queue_results.send(cancel_res);
+
+            // remove the task from the waiting queue
             queue_results.remove_waiting_task_id(id_task);
         }
         // push to beginning of the queue, so it has highest priority
@@ -2632,6 +2643,25 @@ int main(int argc, char ** argv) {
         res_ok(res, health);
     };
 
+    const auto handle_cancel_tasks = [&](const httplib::Request & req, httplib::Response & res) {
+        json request_data = json::parse(req.body);
+        if (!request_data.contains("task_id") || !request_data["task_id"].is_number_integer()) {
+            res.status = 400;
+            res_error(res, format_error_response(
+                "Invalid request: 'task_id' field is required and must be integer",
+                ERROR_TYPE_INVALID_REQUEST
+            ));
+            return;
+        }
+        int task_id = request_data["task_id"].get<int>();
+        ctx_server.cancel_tasks({task_id});
+        json reply = {
+            {"task_id", task_id},
+            {"status", "cancelled"}
+        };
+        res_ok(res, reply);
+    };
+
     const auto handle_slots = [&](const httplib::Request & req, httplib::Response & res) {
         if (!params.endpoint_slots) {
             res_error(res, format_error_response("This server does not support slots endpoint. Start it without `--no-slots`", ERROR_TYPE_NOT_SUPPORTED));
@@ -3324,6 +3354,8 @@ int main(int argc, char ** argv) {
     // Save & load slots
     svr->Get ("/slots",               handle_slots);
     svr->Post("/slots/:id_slot",      handle_slots_action);
+    // Stop tasks
+    svr->Post("/v1/cancel",           handle_cancel_tasks);
 
     //
     // Start the server