server: refactor child --> router communication (#24821)

* server: refactor child --> router communication

* fix wakeup case

* add docs

* improve update_status()

* nits

common/arg.cpp

@@ -303,7 +303,6 @@ static handle_model_result common_params_handle_model(struct common_params_model
 
     if (!model.docker_repo.empty()) {
         model.path = common_docker_resolve_model(model.docker_repo);
-        model.name = model.docker_repo;
     } else if (!model.hf_repo.empty()) {
         // If -m was used with -hf, treat the model "path" as the hf_file to download
         if (model.hf_file.empty() && !model.path.empty()) {
@@ -323,7 +322,6 @@ static handle_model_result common_params_handle_model(struct common_params_model
             throw std::runtime_error("failed to download model from Hugging Face");
         }
 
-        model.name = model.hf_repo;
         model.path = download_result.model_path;
 
         if (!download_result.mmproj_path.empty()) {

common/common.h

@@ -295,7 +295,16 @@ struct common_params_model {
     std::string hf_repo     = ""; // HF repo                                                // NOLINT
     std::string hf_file     = ""; // HF file                                                // NOLINT
     std::string docker_repo = ""; // Docker repo                                            // NOLINT
-    std::string name        = ""; // in format <user>/<model>[:<tag>] (tag is optional)     // NOLINT
+
+    std::string get_name() {
+        if (!hf_repo.empty()) {
+            return hf_repo;
+        }
+        if (!docker_repo.empty()) {
+            return docker_repo;
+        }
+        return path;
+    }
 };
 
 // draft-model-based speculative decoding parameters

tools/server/README-dev.md

@@ -180,6 +180,17 @@ That requires `JSON.stringify` when formatted to message content:
 }
 ```
 
+### Router mode: how child <--> router communicates
+
+Upon spawning a new child process using `subprocess`, both child and router listen to the stdout/stderr (combined)
+
+For the direction from child to router:
+- Generic messages are logs, it will be forwarded to router's stdout
+- Special state update messages are prefixed by `cmd_child_to_router:state:`, followed by a JSON. See `server_models::handle_child_state` for more
+
+For the direction from router to child:
+- When server sends `cmd_router_to_child:exit`, the child should exit gracefully --> if after `DEFAULT_STOP_TIMEOUT` and the child is still running, force-kill it
+
 ### Model management API (router mode)
 
 Model management API was added via PR [#23976](https://github.com/ggml-org/llama.cpp/pull/23976)

tools/server/server-context.cpp

@@ -63,11 +63,6 @@ enum slot_state {
     SLOT_STATE_GENERATING,
 };
 
-enum server_state {
-    SERVER_STATE_LOADING_MODEL,  // Server is starting up, model not fully loaded yet
-    SERVER_STATE_READY,          // Server is ready and model is loaded
-};
-
 struct server_slot {
     int id;
 
@@ -773,6 +768,8 @@ public:
     // note: chat_params must not be refreshed upon existing sleeping state
     server_chat_params chat_params;
 
+    server_state_callback_t callback_state = [](server_state, json) -> void {};
+
     server_context_impl() {
         mtmd_helper_log_set(common_log_default_callback, nullptr);
     }
@@ -1244,8 +1241,8 @@ private:
         if (!params_base.model_alias.empty()) {
             // backward compat: use first alias as model name
             model_name = *params_base.model_alias.begin();
-        } else if (!params_base.model.name.empty()) {
+        } else if (!params_base.model.get_name().empty()) {
-            model_name = params_base.model.name;
+            model_name = params_base.model.get_name();
         } else {
             // fallback: derive model name from file name
             auto model_path = std::filesystem::path(params_base.model.path);
@@ -3734,8 +3731,11 @@ struct server_res_generator : server_http_res {
     }
 };
 
-void server_context::on_sleeping_changed(std::function<void(bool)> callback) {
+void server_context::set_state_callback(server_state_callback_t callback) {
-    impl->queue_tasks.on_sleeping_state(std::move(callback));
+    impl->callback_state = std::move(callback);
+    impl->queue_tasks.on_sleeping_state([this](bool sleeping) {
+        impl->callback_state(sleeping ? SERVER_STATE_SLEEPING : SERVER_STATE_READY, {});
+    });
 }
 
 // compute the number of tokens before the last user message in the prompt

tools/server/server-context.h

@@ -52,6 +52,31 @@ struct server_context_meta {
     uint64_t model_size;
 };
 
+enum server_state {
+    // SERVER_STATE_DOWNLOADING,
+    SERVER_STATE_LOADING,
+    SERVER_STATE_READY,
+    SERVER_STATE_SLEEPING,
+};
+
+static std::string server_state_to_str(server_state state) {
+    switch (state) {
+        case SERVER_STATE_LOADING:     return "loading";
+        case SERVER_STATE_READY:       return "ready";
+        case SERVER_STATE_SLEEPING:    return "sleeping";
+        default: GGML_ASSERT(false && "invalid server_state");
+    }
+}
+
+static server_state server_state_from_str(const std::string & str) {
+    if (str == "loading")     return SERVER_STATE_LOADING;
+    if (str == "ready")       return SERVER_STATE_READY;
+    if (str == "sleeping")    return SERVER_STATE_SLEEPING;
+    GGML_ASSERT(false && "invalid server_state string");
+}
+
+using server_state_callback_t = std::function<void(server_state, json /* payload */)>;
+
 struct server_context {
     std::unique_ptr<server_context_impl> impl;
 
@@ -79,9 +104,8 @@ struct server_context {
     // not thread-safe, should only be used from the main thread
     server_context_meta get_meta() const;
 
-    // register a callback to be called when sleeping state changes
+    // note: must be set before load_model() is called
-    // must be set before load_model() is called
+    void set_state_callback(server_state_callback_t callback);
-    void on_sleeping_changed(std::function<void(bool)> callback);
 };
 
 

tools/server/server-models.cpp

@@ -1,5 +1,6 @@
 #include "server-common.h"
 #include "server-models.h"
+#include "server-context.h"
 
 #include "build-info.h"
 #include "preset.h"
@@ -44,9 +45,7 @@ extern char **environ;
 #define DEFAULT_STOP_TIMEOUT 10 // seconds
 
 #define CMD_ROUTER_TO_CHILD_EXIT  "cmd_router_to_child:exit"
-#define CMD_CHILD_TO_ROUTER_READY "cmd_child_to_router:ready" // also sent when waking up from sleep
+#define CMD_CHILD_TO_ROUTER_STATE "cmd_child_to_router:state:" // followed by json string
-#define CMD_CHILD_TO_ROUTER_SLEEP "cmd_child_to_router:sleep"
-#define CMD_CHILD_TO_ROUTER_INFO  "cmd_child_to_router:info:" // followed by json string
 
 // address for child process, this is needed because router may run on 0.0.0.0
 // ref: https://github.com/ggml-org/llama.cpp/issues/17862
@@ -904,12 +903,8 @@ void server_models::load(const std::string & name) {
                 while (fgets(buffer, vec_buf.size(), stdout_file) != nullptr) {
                     LOG("[%5d] %s", port, buffer);
                     std::string str(buffer);
-                    if (string_starts_with(buffer, CMD_CHILD_TO_ROUTER_READY)) {
+                    if (string_starts_with(buffer, CMD_CHILD_TO_ROUTER_STATE)) {
-                        this->update_status(name, SERVER_MODEL_STATUS_LOADED, 0);
+                        this->handle_child_state(name, str);
-                    } else if (string_starts_with(buffer, CMD_CHILD_TO_ROUTER_INFO)) {
-                        this->update_loaded_info(name, str);
-                    } else if (string_starts_with(buffer, CMD_CHILD_TO_ROUTER_SLEEP)) {
-                        this->update_status(name, SERVER_MODEL_STATUS_SLEEPING, 0);
                     }
                 }
             } else {
@@ -976,7 +971,10 @@ void server_models::load(const std::string & name) {
         subprocess_destroy(&child_proc->get());
 
         // update status and exit code
-        this->update_status(name, SERVER_MODEL_STATUS_UNLOADED, exit_code);
+        this->update_status(name, {
+            SERVER_MODEL_STATUS_UNLOADED,
+            exit_code
+        });
         SRV_INF("instance name=%s exited with status %d\n", name.c_str(), exit_code);
     });
 
@@ -1016,7 +1014,8 @@ struct server_models_download_res : public common_download_callback {
             common_download_model(model, opts);
             is_ok = true;
         } catch (const std::exception & e) {
-            SRV_ERR("download failed for model name=%s: %s\n", model.name.c_str(), e.what());
+            auto model_name = model.get_name();
+            SRV_ERR("download failed for model name=%s: %s\n", model_name.c_str(), e.what());
             is_ok = false;
         }
         return is_ok;
@@ -1036,7 +1035,7 @@ struct server_models_download_res : public common_download_callback {
 };
 
 void server_models::download(common_params_model && model, common_download_opts && opts) {
-    std::string name = model.name;
+    std::string name = model.get_name();
     GGML_ASSERT(name == model.hf_repo);
 
     std::unique_lock<std::mutex> lk(mutex);
@@ -1064,9 +1063,10 @@ void server_models::download(common_params_model && model, common_download_opts
     inst.th = std::thread([this, dl = std::move(dl)]() {
         dl->opts.callback = dl.get();
         bool ok = dl->run();
+        auto model_name = dl->model.get_name();
         SRV_INF("download finished for model name=%s with status=%s\n",
-                    dl->model.name.c_str(), ok ? "success" : "failure");
+                    model_name.c_str(), ok ? "success" : "failure");
-        update_download_progress(dl->model.name, {}, true, ok);
+        update_download_progress(model_name, {}, true, ok);
         // need_reload is set inside update_download_progress under the mutex;
         // the next load_models() call will clean up this instance
     });
@@ -1130,21 +1130,27 @@ void server_models::unload_all() {
     }
 }
 
-void server_models::update_status(const std::string & name, server_model_status status, int exit_code) {
+void server_models::update_status(const std::string & name, const update_status_args & args) {
     std::unique_lock<std::mutex> lk(mutex);
     auto it = mapping.find(name);
     if (it != mapping.end()) {
         auto & meta = it->second.meta;
-        meta.status    = status;
+        meta.status      = args.status;
-        meta.exit_code = exit_code;
+        meta.exit_code   = args.exit_code;
+        if (!args.loaded_info.is_null()) {
+            meta.loaded_info = args.loaded_info;
+        }
     }
     // broadcast status change to SSE
     {
         json data = {
-            {"status", server_model_status_to_string(status)},
+            {"status", server_model_status_to_string(args.status)},
         };
-        if (status == SERVER_MODEL_STATUS_UNLOADED) {
+        if (args.status == SERVER_MODEL_STATUS_UNLOADED) {
-            data["exit_code"] = exit_code;
+            data["exit_code"] = args.exit_code;
+        }
+        if (!args.loaded_info.is_null()) {
+            data["info"] = args.loaded_info;
         }
         // note: notify_sse doesn't acquire the lock, so no deadlock here
         notify_sse("status_change", name, data);
@@ -1152,29 +1158,6 @@ void server_models::update_status(const std::string & name, server_model_status
     cv.notify_all();
 }
 
-void server_models::update_loaded_info(const std::string & name, std::string & raw_info) {
-    if (!string_starts_with(raw_info, CMD_CHILD_TO_ROUTER_INFO)) {
-        SRV_WRN("invalid loaded info format from child for model name=%s: %s\n", name.c_str(), raw_info.c_str());
-        return;
-    }
-
-    json info;
-    try {
-        info = json::parse(raw_info.substr(strlen(CMD_CHILD_TO_ROUTER_INFO)));
-    } catch (const std::exception & e) {
-        SRV_WRN("failed to parse loaded info from child for model name=%s: %s\n", name.c_str(), e.what());
-        return;
-    }
-
-    std::unique_lock<std::mutex> lk(mutex);
-    auto it = mapping.find(name);
-    if (it != mapping.end()) {
-        auto & meta = it->second.meta;
-        meta.loaded_info = info;
-    }
-    cv.notify_all();
-}
-
 void server_models::update_download_progress(const std::string & name, const common_download_progress & progress, bool done, bool ok) {
     json curr;
     {
@@ -1323,21 +1306,54 @@ server_http_res_ptr server_models::proxy_request(const server_http_req & req, co
     return proxy;
 }
 
-bool server_models::is_child_server() {
+void server_models::handle_child_state(const std::string & name, const std::string & raw_input) {
+    server_state state;
+    json payload;
+
+    try {
+        json data = json::parse(raw_input.substr(strlen(CMD_CHILD_TO_ROUTER_STATE)));
+        state = server_state_from_str(json_value(data, "state", std::string()));
+        payload = json_value(data, "payload", json{});
+    } catch (const std::exception & e) {
+        SRV_ERR("failed to parse child state update for name=%s: %s\n", name.c_str(), e.what());
+        return;
+    }
+
+    switch (state) {
+        case SERVER_STATE_LOADING:
+            {
+                // do nothing for now
+                // TODO: report loading progress for first load and wakeup from sleep
+            } break;
+        case SERVER_STATE_READY:
+            {
+                update_status(name, {
+                    SERVER_MODEL_STATUS_LOADED,
+                    0,
+                    // note: payload can be empty if this is a wakeup from sleep
+                    payload.size() > 0 ? payload : nullptr
+                });
+            } break;
+        case SERVER_STATE_SLEEPING:
+            {
+                update_status(name, { SERVER_MODEL_STATUS_SLEEPING });
+            } break;
+        default:
+            // should never happen, but just in case
+            GGML_ASSERT(false && "unexpected state from child server");
+    }
+}
+
+//
+// server_child
+//
+
+bool server_child::is_child() {
     const char * router_port = std::getenv("LLAMA_SERVER_ROUTER_PORT");
     return router_port != nullptr;
 }
 
-std::thread server_models::setup_child_server(const std::function<void(int)> & shutdown_handler, const json & model_info) {
+std::thread server_child::setup(const std::function<void(int)> & shutdown_handler) {
-    // send a notification to the router server that a model instance is ready
-    common_log_pause(common_log_main());
-    fflush(stdout);
-    fprintf(stdout, "%s\n", CMD_CHILD_TO_ROUTER_READY);
-    fflush(stdout);
-    fprintf(stdout, "%s%s\n", CMD_CHILD_TO_ROUTER_INFO, safe_json_to_str(model_info).c_str());
-    fflush(stdout);
-    common_log_resume(common_log_main());
-
     // setup thread for monitoring stdin
     return std::thread([shutdown_handler]() {
         // wait for EOF on stdin
@@ -1363,10 +1379,14 @@ std::thread server_models::setup_child_server(const std::function<void(int)> & s
     });
 }
 
-void server_models::notify_router_sleeping_state(bool is_sleeping) {
+void server_child::notify_to_router(const std::string & state, const json & payload) {
+    json data = {
+        {"state", state},
+        {"payload", payload},
+    };
     common_log_pause(common_log_main());
     fflush(stdout);
-    fprintf(stdout, "%s\n", is_sleeping ? CMD_CHILD_TO_ROUTER_SLEEP : CMD_CHILD_TO_ROUTER_READY);
+    fprintf(stdout, "%s%s\n", CMD_CHILD_TO_ROUTER_STATE, safe_json_to_str(data).c_str());
     fflush(stdout);
     common_log_resume(common_log_main());
 }
@@ -1644,7 +1664,6 @@ void server_models_routes::init_routes() {
         common_params_model model;
         common_download_opts opts;
 
-        model.name           = name;
         model.hf_repo        = name;
         opts.bearer_token    = params.hf_token;
         opts.download_mmproj = true;

tools/server/server-models.h

@@ -171,8 +171,12 @@ public:
     void download(common_params_model && model, common_download_opts && opts);
 
     // update the status of a model instance (thread-safe)
-    void update_status(const std::string & name, server_model_status status, int exit_code);
+    struct update_status_args {
-    void update_loaded_info(const std::string & name, std::string & raw_info);
+        server_model_status status;
+        int exit_code = 0; // only valid if status == UNLOADED
+        json loaded_info = nullptr;
+    };
+    void update_status(const std::string & name, const update_status_args & args);
     void update_download_progress(const std::string & name, const common_download_progress & progress, bool done, bool ok = true);
 
     // remove a cache model from disk and update the list (thread-safe)
@@ -193,15 +197,27 @@ public:
     // proxy an HTTP request to the model instance
     server_http_res_ptr proxy_request(const server_http_req & req, const std::string & method, const std::string & name, bool update_last_used);
 
+    // handle message sent from server_child::notify_to_router()
+    // raw input must starts with CMD_CHILD_TO_ROUTER_STATE, followed by a JSON string
+    // this function is not thread-safe, must be called from instance's monitoring thread
+    // payload per state:
+    //     state = loading     -> payload = {} (TODO: add progress info)
+    //     state = ready       -> payload = model_info (json), or {} if wakeup from sleeping
+    //     state = sleeping    -> payload = {}
+    void handle_child_state(const std::string & name, const std::string & raw_input);
+};
+
+struct server_child {
     // return true if the current process is a child server instance
-    static bool is_child_server();
+    bool is_child();
 
-    // notify the router server that a model instance is ready
+    // register the shutdown_handler to be called by the router
     // return the monitoring thread (to be joined by the caller)
-    static std::thread setup_child_server(const std::function<void(int)> & shutdown_handler, const json & model_info);
+    std::thread setup(const std::function<void(int)> & shutdown_handler);
 
-    // notify the router server that the sleeping state has changed
+    // notify router server for status changes (e.g. loading, downloading, sleeping, etc.)
-    static void notify_router_sleeping_state(bool sleeping);
+    // message will be handled by server_models::handle_child_state() on the router side
+    void notify_to_router(const std::string & state_name, const json & payload);
 };
 
 struct server_models_routes {

tools/server/server.cpp

@@ -90,8 +90,10 @@ int llama_server(int argc, char ** argv) {
     llama_numa_init(params.numa);
 
     // router server never loads a model and must not touch the GPU
+    const bool is_router_server = params.model.path.empty()
+                               && params.model.hf_repo.empty();
+
     // skip device enumeration so the CUDA primary context stays uncreated
-    const bool is_router_server = params.model.path.empty();
     common_params_print_info(params, !is_router_server);
 
     if (!is_router_server) {
@@ -113,8 +115,9 @@ int llama_server(int argc, char ** argv) {
     }
 
     // for consistency between server router mode and single-model mode, we set the same model name as alias
-    if (params.model_alias.empty() && !params.model.name.empty()) {
+    auto model_name = params.model.get_name();
-        params.model_alias.insert(params.model.name);
+    if (params.model_alias.empty() && !model_name.empty()) {
+        params.model_alias.insert(model_name);
     }
 
     // struct that contains llama context and inference
@@ -255,6 +258,7 @@ int llama_server(int argc, char ** argv) {
     // Start the server
     //
 
+    server_child child; // only used in non-router mode
     std::function<void()> clean_up;
 
     if (is_router_server) {
@@ -300,15 +304,16 @@ int llama_server(int argc, char ** argv) {
             return 1;
         }
 
-        // load the model
+        // setup communication child --> router if necessary
-        SRV_INF("%s", "loading model\n");
+        if (child.is_child()) {
-
+            ctx_server.set_state_callback([&](server_state state, json payload) {
-        if (server_models::is_child_server()) {
+                child.notify_to_router(server_state_to_str(state), payload);
-            ctx_server.on_sleeping_changed([&](bool sleeping) {
-                server_models::notify_router_sleeping_state(sleeping);
             });
         }
 
+        // load the model
+        SRV_INF("%s", "loading model\n");
+
         if (!ctx_server.load_model(params)) {
             clean_up();
             if (ctx_http.thread.joinable()) {
@@ -365,9 +370,9 @@ int llama_server(int argc, char ** argv) {
 
         // optionally, notify router server that this instance is ready
         std::thread monitor_thread;
-        if (server_models::is_child_server()) {
+        if (child.is_child()) {
-            json model_info = routes.get_model_info();
+            monitor_thread = child.setup(shutdown_handler);
-            monitor_thread = server_models::setup_child_server(shutdown_handler, model_info);
+            child.notify_to_router(server_state_to_str(SERVER_STATE_READY), routes.get_model_info());
         }
 
         // this call blocks the main thread until queue_tasks.terminate() is called