rpc : enable async operations

Start a dedicated backend thread in the rpc-server and use message
passing interface for submitting work to it. This will enable backend
async operations and cross-server communication.

ggml-rpc.cpp

@@ -5,8 +5,11 @@
 #include <cinttypes>
 #include <string>
 #include <vector>
+#include <queue>
 #include <memory>
 #include <mutex>
+#include <thread>
+#include <condition_variable>
 #include <unordered_map>
 #include <unordered_set>
 #ifdef _WIN32
@@ -17,6 +20,7 @@
 #  include <windows.h>
 #  include <winsock2.h>
 #else
+#  include <signal.h>
 #  include <arpa/inet.h>
 #  include <sys/socket.h>
 #  include <sys/types.h>
@@ -93,6 +97,7 @@ enum rpc_cmd {
     COPY_TENSOR,
     GRAPH_COMPUTE,
     GET_DEVICE_MEMORY,
+    FREE_ALL_BUFFERS,
 };
 
 // RPC data structures
@@ -739,6 +744,48 @@ GGML_API GGML_CALL void ggml_backend_rpc_get_device_memory(const char * endpoint
 
 // RPC server-side implementation
 
+template <typename T>
+class message_queue {
+    std::queue<T> queue;
+    std::mutex mutex;
+    std::condition_variable cvar;
+
+public:
+    message_queue() {}
+
+    void push(const T &value) {
+        std::unique_lock<std::mutex> lock(mutex);
+        queue.push(value);
+        lock.unlock();
+        cvar.notify_all();
+    }
+
+    void pop(T* out) {
+        std::unique_lock<std::mutex> lock(mutex);
+        cvar.wait(lock, [this] { return queue.size() > 0; });
+        *out = queue.front();
+        queue.pop();
+    }
+};
+
+struct rpc_response {
+    std::vector<uint8_t> output;
+    bool status;
+};
+
+using rpc_response_ptr = std::shared_ptr<rpc_response>;
+using response_queue = message_queue<rpc_response_ptr>;
+using response_queue_ptr = std::shared_ptr<response_queue>;
+
+struct rpc_request {
+    rpc_cmd cmd;
+    std::vector<uint8_t> input;
+    response_queue_ptr response_queue;
+};
+using rpc_request_ptr = std::shared_ptr<rpc_request>;
+using request_queue = message_queue<rpc_request_ptr>;
+using request_queue_ptr = std::shared_ptr<request_queue>;
+
 class rpc_server {
 public:
     rpc_server(ggml_backend_t backend) : backend(backend) {}
@@ -755,6 +802,7 @@ public:
     bool copy_tensor(const std::vector<uint8_t> & input, std::vector<uint8_t> & output);
     bool graph_compute(const std::vector<uint8_t> & input, std::vector<uint8_t> & output);
 
+    void free_all_buffers();
 private:
     ggml_tensor * deserialize_tensor(struct ggml_context * ctx, const rpc_tensor * tensor);
     ggml_tensor * create_node(uint64_t id,
@@ -1051,76 +1099,122 @@ bool rpc_server::graph_compute(const std::vector<uint8_t> & input, std::vector<u
     return true;
 }
 
-rpc_server::~rpc_server() {
+void rpc_server::free_all_buffers() {
     for (auto buffer : buffers) {
         ggml_backend_buffer_free(buffer);
     }
+    buffers.clear();
 }
 
-static void rpc_serve_client(ggml_backend_t backend, sockfd_t sockfd, size_t free_mem, size_t total_mem) {
+rpc_server::~rpc_server() {
+    free_all_buffers();
+}
+
+static void process_requests(ggml_backend_t backend, request_queue_ptr requestq) {
     rpc_server server(backend);
+    while (true) {
+        rpc_request_ptr request;
+        requestq->pop(&request);
+        rpc_response_ptr response = std::make_shared<rpc_response>();
+        bool ok = true;
+        switch (request->cmd) {
+            case ALLOC_BUFFER: {
+                ok = server.alloc_buffer(request->input, response->output);
+                break;
+            }
+            case GET_ALIGNMENT: {
+                server.get_alignment(response->output);
+                break;
+            }
+            case GET_MAX_SIZE: {
+                server.get_max_size(response->output);
+                break;
+            }
+            case BUFFER_GET_BASE: {
+                ok = server.buffer_get_base(request->input, response->output);
+                break;
+            }
+            case FREE_BUFFER: {
+                ok = server.free_buffer(request->input);
+                break;
+            }
+            case BUFFER_CLEAR: {
+                ok = server.buffer_clear(request->input);
+                break;
+            }
+            case SET_TENSOR: {
+                ok = server.set_tensor(request->input);
+                break;
+            }
+            case GET_TENSOR: {
+                ok = server.get_tensor(request->input, response->output);
+                break;
+            }
+            case COPY_TENSOR: {
+                ok = server.copy_tensor(request->input, response->output);
+                break;
+            }
+            case GRAPH_COMPUTE: {
+                ok = server.graph_compute(request->input, response->output);
+                break;
+            }
+            case GET_DEVICE_MEMORY: {
+                break;
+            }
+            case FREE_ALL_BUFFERS: {
+                server.free_all_buffers();
+                continue;
+            }
+            default: {
+                fprintf(stderr, "Unknown command: %d\n", request->cmd);
+                ok = false;
+            }
+        }
+        response->status = ok;
+        request->response_queue->push(response);
+    }
+}
+
+static void rpc_serve_client(request_queue_ptr requestq, sockfd_t sockfd, size_t free_mem, size_t total_mem) {
+    auto responseq = std::make_shared<response_queue>();
     while (true) {
         uint8_t cmd;
         if (!recv_data(sockfd, &cmd, 1)) {
             break;
         }
-        std::vector<uint8_t> input;
+        auto request = std::make_shared<rpc_request>();
-        std::vector<uint8_t> output;
+        request->cmd = (rpc_cmd)cmd;
+        request->response_queue = responseq;
         uint64_t input_size;
         if (!recv_data(sockfd, &input_size, sizeof(input_size))) {
             break;
         }
-        input.resize(input_size);
+        request->input.resize(input_size);
-        if (!recv_data(sockfd, input.data(), input_size)) {
+        if (!recv_data(sockfd, request->input.data(), input_size)) {
             break;
         }
         bool ok = true;
+        auto response = std::make_shared<rpc_response>();
         switch (cmd) {
-            case ALLOC_BUFFER: {
+            case ALLOC_BUFFER:
-                ok = server.alloc_buffer(input, output);
+            case GET_ALIGNMENT:
-                break;
+            case GET_MAX_SIZE:
-            }
+            case BUFFER_GET_BASE:
-            case GET_ALIGNMENT: {
+            case FREE_BUFFER:
-                server.get_alignment(output);
+            case BUFFER_CLEAR:
-                break;
+            case SET_TENSOR:
-            }
+            case GET_TENSOR:
-            case GET_MAX_SIZE: {
+            case COPY_TENSOR:
-                server.get_max_size(output);
-                break;
-            }
-            case BUFFER_GET_BASE: {
-                ok = server.buffer_get_base(input, output);
-                break;
-            }
-            case FREE_BUFFER: {
-                ok = server.free_buffer(input);
-                break;
-            }
-            case BUFFER_CLEAR: {
-                ok = server.buffer_clear(input);
-                break;
-            }
-            case SET_TENSOR: {
-                ok = server.set_tensor(input);
-                break;
-            }
-            case GET_TENSOR: {
-                ok = server.get_tensor(input, output);
-                break;
-            }
-            case COPY_TENSOR: {
-                ok = server.copy_tensor(input, output);
-                break;
-            }
             case GRAPH_COMPUTE: {
-                ok = server.graph_compute(input, output);
+                requestq->push(request);
+                responseq->pop(&response);
                 break;
             }
             case GET_DEVICE_MEMORY: {
                 // output serialization format: | free (8 bytes) | total (8 bytes) |
-                output.resize(2*sizeof(uint64_t), 0);
+                response->output.resize(2*sizeof(uint64_t), 0);
-                memcpy(output.data(), &free_mem, sizeof(free_mem));
+                memcpy(response->output.data(), &free_mem, sizeof(free_mem));
-                memcpy(output.data() + sizeof(uint64_t), &total_mem, sizeof(total_mem));
+                memcpy(response->output.data() + sizeof(uint64_t), &total_mem, sizeof(total_mem));
                 break;
             }
             default: {
@@ -1131,17 +1225,29 @@ static void rpc_serve_client(ggml_backend_t backend, sockfd_t sockfd, size_t fre
         if (!ok) {
             break;
         }
-        uint64_t output_size = output.size();
+        uint64_t output_size = response->output.size();
         if (!send_data(sockfd, &output_size, sizeof(output_size))) {
             break;
         }
-        if (!send_data(sockfd, output.data(), output_size)) {
+        if (!send_data(sockfd, response->output.data(), output_size)) {
             break;
         }
     }
+    auto request = std::make_shared<rpc_request>();
+    request->cmd = FREE_ALL_BUFFERS;
+    requestq->push(request);
 }
 
 void start_rpc_server(ggml_backend_t backend, const char * endpoint, size_t free_mem, size_t total_mem) {
+#ifndef _WIN32
+    // prevent SIGPIPE when writing to closed socket
+    signal(SIGPIPE, SIG_IGN);
+#endif
+    auto requestq = std::make_shared<request_queue>();
+    std::thread backend_thread = std::thread([=] {
+        process_requests(backend, requestq);
+    });
+
     std::string host;
     int port;
     if (!parse_endpoint(endpoint, host, port)) {
@@ -1169,7 +1275,7 @@ void start_rpc_server(ggml_backend_t backend, const char * endpoint, size_t free
             return;
         }
         printf("Accepted client connection, free_mem=%zu, total_mem=%zu\n", free_mem, total_mem);
-        rpc_serve_client(backend, client_socket->fd, free_mem, total_mem);
+        rpc_serve_client(requestq, client_socket->fd, free_mem, total_mem);
         printf("Client connection closed\n");
     }
 #ifdef _WIN32