ggml-rpc.cpp

#include "ggml-rpc.h"
#include "ggml.h"
#include "ggml-backend-impl.h"

#include <cinttypes>
#include <string>
#include <vector>
#include <memory>
#include <mutex>
#include <unordered_map>
#include <unordered_set>
#ifdef _WIN32
# define WIN32_LEAN_AND_MEAN
# ifndef NOMINMAX
# define NOMINMAX
# endif
# include <windows.h>
# include <winsock2.h>
#else
# include <arpa/inet.h>
# include <sys/socket.h>
# include <sys/types.h>
# include <netinet/in.h>
# include <netinet/tcp.h>
# include <netdb.h>
# include <unistd.h>
#endif
#include <string.h>

#define UNUSED GGML_UNUSED

#define GGML_DEBUG 0
#if (GGML_DEBUG >= 1)
#define GGML_PRINT_DEBUG(...) printf(__VA_ARGS__)
#else
#define GGML_PRINT_DEBUG(...)
#endif

#ifdef _WIN32
typedef SOCKET sockfd_t;
using ssize_t = __int64;
#else
typedef int sockfd_t;
#endif

// cross-platform socket
struct socket_t {
 sockfd_t fd;
 socket_t(sockfd_t fd) : fd(fd) {}
 ~socket_t() {
 GGML_PRINT_DEBUG("[%s] closing socket %d\n", __func__, this->fd);
#ifdef _WIN32
 closesocket(this->fd);
#else
 close(this->fd);
#endif
 }
};

// ggml_tensor is serialized into rpc_tensor
#pragma pack(push, 1)
struct rpc_tensor {
 uint64_t id;
 uint32_t type;
 uint64_t buffer;
 uint32_t ne[GGML_MAX_DIMS];
 uint32_t nb[GGML_MAX_DIMS];
 uint32_t op;
 int32_t op_params[GGML_MAX_OP_PARAMS / sizeof(int32_t)];
 int32_t flags;
 uint64_t src[GGML_MAX_SRC];
 uint64_t view_src;
 uint64_t view_offs;
 uint64_t data;
 char name[GGML_MAX_NAME];
};
#pragma pack(pop)

// RPC commands
enum rpc_cmd {
 ALLOC_BUFFER = 0,
 GET_ALIGNMENT,
 GET_MAX_SIZE,
 BUFFER_GET_BASE,
 FREE_BUFFER,
 BUFFER_CLEAR,
 SET_TENSOR,
 GET_TENSOR,
 COPY_TENSOR,
 GRAPH_COMPUTE,
 GET_DEVICE_MEMORY,
};

// RPC data structures

static ggml_guid_t ggml_backend_rpc_guid() {
 static ggml_guid guid = {0x99, 0x68, 0x5b, 0x6c, 0xd2, 0x83, 0x3d, 0x24, 0x25, 0x36, 0x72, 0xe1, 0x5b, 0x0e, 0x14, 0x03};
 return &guid;
}

struct ggml_backend_rpc_buffer_type_context {
 std::string endpoint;
 std::string name;
 size_t alignment;
 size_t max_size;
};

struct ggml_backend_rpc_context {
 std::string endpoint;
 std::string name;
};

struct ggml_backend_rpc_buffer_context {
 std::shared_ptr<socket_t> sock;
 std::unordered_map<ggml_backend_buffer_t, void *> base_cache;
 uint64_t remote_ptr;
 std::string name;
};

// RPC helper functions

static std::shared_ptr<socket_t> make_socket(sockfd_t fd) {
#ifdef _WIN32
 if (fd == INVALID_SOCKET) {
 return nullptr;
 }
#else
 if (fd < 0) {
 return nullptr;
 }
#endif
 return std::make_shared<socket_t>(fd);
}

static bool set_no_delay(sockfd_t sockfd) {
 int flag = 1;
 // set TCP_NODELAY to disable Nagle's algorithm
 int ret = setsockopt(sockfd, IPPROTO_TCP, TCP_NODELAY, (char *)&flag, sizeof(int));
 return ret == 0;
}

static bool set_reuse_addr(sockfd_t sockfd) {
 int flag = 1;
 int ret = setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, (char *)&flag, sizeof(int));
 return ret == 0;
}

static std::shared_ptr<socket_t> socket_connect(const char * host, int port) {
 struct sockaddr_in addr;
 auto sockfd = socket(AF_INET, SOCK_STREAM, 0);
 auto sock_ptr = make_socket(sockfd);
 if (sock_ptr == nullptr) {
 return nullptr;
 }
 if (!set_no_delay(sockfd)) {
 fprintf(stderr, "Failed to set TCP_NODELAY\n");
 return nullptr;
 }
 addr.sin_family = AF_INET;
 addr.sin_port = htons(port);
 struct hostent * server = gethostbyname(host);
 if (server == NULL) {
 fprintf(stderr, "Cannot resolve host '%s'\n", host);
 return nullptr;
 }
 memcpy(&addr.sin_addr.s_addr, server->h_addr, server->h_length);
 if (connect(sock_ptr->fd, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
 return nullptr;
 }
 return sock_ptr;
}

static std::shared_ptr<socket_t> socket_accept(sockfd_t srv_sockfd) {
 auto client_socket_fd = accept(srv_sockfd, NULL, NULL);
 auto client_socket = make_socket(client_socket_fd);
 if (client_socket == nullptr) {
 return nullptr;
 }
 if (!set_no_delay(client_socket_fd)) {
 fprintf(stderr, "Failed to set TCP_NODELAY\n");
 return nullptr;
 }
 return client_socket;
}

static std::shared_ptr<socket_t> create_server_socket(const char * host, int port) {
 auto sockfd = socket(AF_INET, SOCK_STREAM, 0);
 auto sock = make_socket(sockfd);
 if (sock == nullptr) {
 return nullptr;
 }
 if (!set_reuse_addr(sockfd)) {
 fprintf(stderr, "Failed to set SO_REUSEADDR\n");
 return nullptr;
 }
 struct sockaddr_in serv_addr;
 serv_addr.sin_family = AF_INET;
 serv_addr.sin_addr.s_addr = inet_addr(host);
 serv_addr.sin_port = htons(port);

 if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0) {
 return nullptr;
 }
 if (listen(sockfd, 1) < 0) {
 return nullptr;
 }
 return sock;
}

static bool send_data(sockfd_t sockfd, const void * data, size_t size) {
 size_t bytes_sent = 0;
 while (bytes_sent < size) {
 ssize_t n = send(sockfd, (const char *)data + bytes_sent, size - bytes_sent, 0);
 if (n < 0) {
 return false;
 }
 bytes_sent += n;
 }
 return true;
}

static bool recv_data(sockfd_t sockfd, void * data, size_t size) {
 size_t bytes_recv = 0;
 while (bytes_recv < size) {
 ssize_t n = recv(sockfd, (char *)data + bytes_recv, size - bytes_recv, 0);
 if (n <= 0) {
 return false;
 }
 bytes_recv += n;
 }
 return true;
}

static bool parse_endpoint(const std::string & endpoint, std::string & host, int & port) {
 size_t pos = endpoint.find(':');
 if (pos == std::string::npos) {
 return false;
 }
 host = endpoint.substr(0, pos);
 port = std::stoi(endpoint.substr(pos + 1));
 return true;
}

// RPC request : | rpc_cmd (1 byte) | request_size (8 bytes) | request_data (request_size bytes) |
// RPC response: | response_size (8 bytes) | response_data (response_size bytes) |
static bool send_rpc_cmd(const std::shared_ptr<socket_t> & sock, enum rpc_cmd cmd, const std::vector<uint8_t> & input, std::vector<uint8_t> & output) {
 uint8_t cmd_byte = cmd;
 if (!send_data(sock->fd, &cmd_byte, sizeof(cmd_byte))) {
 return false;
 }
 uint64_t input_size = input.size();
 if (!send_data(sock->fd, &input_size, sizeof(input_size))) {
 return false;
 }
 if (!send_data(sock->fd, input.data(), input.size())) {
 return false;
 }
 uint64_t output_size;
 if (!recv_data(sock->fd, &output_size, sizeof(output_size))) {
 return false;
 }
 if (output_size == 0) {
 output.clear();
 return true;
 }
 output.resize(output_size);
 if (!recv_data(sock->fd, output.data(), output_size)) {
 return false;
 }
 return true;
}

// RPC client-side implementation

static std::shared_ptr<socket_t> get_socket(const std::string & endpoint) {
 static std::mutex mutex;
 std::lock_guard<std::mutex> lock(mutex);
 static std::unordered_map<std::string, std::weak_ptr<socket_t>> sockets;
 static bool initialized = false;

 auto it = sockets.find(endpoint);
 if (it != sockets.end()) {
 if (auto sock = it->second.lock()) {
 return sock;
 }
 }
 std::string host;
 int port;
 if (!parse_endpoint(endpoint, host, port)) {
 return nullptr;
 }
#ifdef _WIN32
 if (!initialized) {
 WSADATA wsaData;
 int res = WSAStartup(MAKEWORD(2, 2), &wsaData);
 if (res != 0) {
 return nullptr;
 }
 initialized = true;
 }
#else
 UNUSED(initialized);
#endif
 auto sock = socket_connect(host.c_str(), port);
 if (sock == nullptr) {
 return nullptr;
 }
 GGML_PRINT_DEBUG("[%s] connected to %s, sockfd=%d\n", __func__, endpoint.c_str(), sock->fd);
 sockets[endpoint] = sock;
 return sock;
}

GGML_CALL static const char * ggml_backend_rpc_buffer_get_name(ggml_backend_buffer_t buffer) {
 ggml_backend_rpc_buffer_context * ctx = (ggml_backend_rpc_buffer_context *)buffer->context;
 return ctx->name.c_str();
}

GGML_CALL static void ggml_backend_rpc_buffer_free_buffer(ggml_backend_buffer_t buffer) {
 ggml_backend_rpc_buffer_context * ctx = (ggml_backend_rpc_buffer_context *)buffer->context;
 // input serialization format: | remote_ptr (8 bytes) |
 std::vector<uint8_t> input(sizeof(uint64_t), 0);
 uint64_t remote_ptr = ctx->remote_ptr;
 memcpy(input.data(), &remote_ptr, sizeof(remote_ptr));
 std::vector<uint8_t> output;
 bool status = send_rpc_cmd(ctx->sock, FREE_BUFFER, input, output);
 GGML_ASSERT(status);
 GGML_ASSERT(output.empty());
 delete ctx;
}

GGML_CALL static void * ggml_backend_rpc_buffer_get_base(ggml_backend_buffer_t buffer) {
 ggml_backend_rpc_buffer_context * ctx = (ggml_backend_rpc_buffer_context *)buffer->context;
 if (ctx->base_cache.find(buffer) != ctx->base_cache.end()) {
 return ctx->base_cache[buffer];
 }
 // input serialization format: | remote_ptr (8 bytes) |
 std::vector<uint8_t> input(sizeof(uint64_t), 0);
 uint64_t remote_ptr = ctx->remote_ptr;
 memcpy(input.data(), &remote_ptr, sizeof(remote_ptr));
 std::vector<uint8_t> output;
 bool status = send_rpc_cmd(ctx->sock, BUFFER_GET_BASE, input, output);
 GGML_ASSERT(status);
 GGML_ASSERT(output.size() == sizeof(uint64_t));
 // output serialization format: | base_ptr (8 bytes) |
 uint64_t base_ptr;
 memcpy(&base_ptr, output.data(), sizeof(base_ptr));
 void * base = reinterpret_cast<void *>(base_ptr);
 ctx->base_cache[buffer] = base;
 return base;
}

static rpc_tensor serialize_tensor(const ggml_tensor * tensor) {
 rpc_tensor result;
 result.id = reinterpret_cast<uint64_t>(tensor);
 result.type = tensor->type;
 if (tensor->buffer) {
 ggml_backend_buffer_t buffer = tensor->buffer;
 ggml_backend_rpc_buffer_context * ctx = (ggml_backend_rpc_buffer_context *)buffer->context;
 result.buffer = ctx->remote_ptr;
 } else {
 result.buffer = 0;
 }
 for (uint32_t i = 0; i < GGML_MAX_DIMS; i++) {
 result.ne[i] = tensor->ne[i];
 result.nb[i] = tensor->nb[i];
 }
 result.op = tensor->op;
 for (uint32_t i = 0; i < GGML_MAX_OP_PARAMS / sizeof(int32_t); i++) {
 result.op_params[i] = tensor->op_params[i];
 }
 result.flags = tensor->flags;
 for (uint32_t i = 0; i < GGML_MAX_SRC; i++) {
 result.src[i] = reinterpret_cast<uint64_t>(tensor->src[i]);
 }
 result.view_src = reinterpret_cast<uint64_t>(tensor->view_src);
 result.view_offs = tensor->view_offs;
 result.data = reinterpret_cast<uint64_t>(tensor->data);
 snprintf(result.name, GGML_MAX_NAME, "%s", tensor->name);
 return result;
}

GGML_CALL static void ggml_backend_rpc_buffer_init_tensor(ggml_backend_buffer_t buffer, ggml_tensor * tensor) {
 UNUSED(buffer);
 if (ggml_is_quantized(tensor->type)) {
 // TODO: this check is due to MATRIX_ROW_PADDING in CUDA and should be generalized
 GGML_ASSERT(tensor->ne[0] % 512 == 0 && "unsupported quantized tensor");
 }
}

GGML_CALL static void ggml_backend_rpc_buffer_set_tensor(ggml_backend_buffer_t buffer, ggml_tensor * tensor, const void * data, size_t offset, size_t size) {
 ggml_backend_rpc_buffer_context * ctx = (ggml_backend_rpc_buffer_context *)buffer->context;
 // input serialization format: | rpc_tensor | offset (8 bytes) | data (size bytes) |
 size_t input_size = sizeof(rpc_tensor) + sizeof(uint64_t) + size;
 std::vector<uint8_t> input(input_size, 0);
 rpc_tensor rpc_tensor = serialize_tensor(tensor);
 memcpy(input.data(), &rpc_tensor, sizeof(rpc_tensor));
 memcpy(input.data() + sizeof(rpc_tensor), &offset, sizeof(offset));
 memcpy(input.data() + sizeof(rpc_tensor) + sizeof(offset), data, size);
 std::vector<uint8_t> output;
 bool status = send_rpc_cmd(ctx->sock, SET_TENSOR, input, output);
 GGML_ASSERT(status);
}

GGML_CALL static void ggml_backend_rpc_buffer_get_tensor(ggml_backend_buffer_t buffer, const ggml_tensor * tensor, void * data, size_t offset, size_t size) {
 ggml_backend_rpc_buffer_context * ctx = (ggml_backend_rpc_buffer_context *)buffer->context;
 // input serialization format: | rpc_tensor | offset (8 bytes) | size (8 bytes) |
 int input_size = sizeof(rpc_tensor) + 2*sizeof(uint64_t);
 std::vector<uint8_t> input(input_size, 0);
 rpc_tensor rpc_tensor = serialize_tensor(tensor);
 memcpy(input.data(), &rpc_tensor, sizeof(rpc_tensor));
 memcpy(input.data() + sizeof(rpc_tensor), &offset, sizeof(offset));
 memcpy(input.data() + sizeof(rpc_tensor) + sizeof(offset), &size, sizeof(size));
 std::vector<uint8_t> output;
 bool status = send_rpc_cmd(ctx->sock, GET_TENSOR, input, output);
 GGML_ASSERT(status);
 GGML_ASSERT(output.size() == size);
 // output serialization format: | data (size bytes) |
 memcpy(data, output.data(), size);
}

GGML_CALL static bool ggml_backend_rpc_buffer_cpy_tensor(ggml_backend_buffer_t buffer, const ggml_tensor * src, ggml_tensor * dst) {
 // check if src and dst are on the same server
 ggml_backend_buffer_t src_buffer = src->buffer;
 ggml_backend_rpc_buffer_context * src_ctx = (ggml_backend_rpc_buffer_context *)src_buffer->context;
 ggml_backend_buffer_t dst_buffer = dst->buffer;
 ggml_backend_rpc_buffer_context * dst_ctx = (ggml_backend_rpc_buffer_context *)dst_buffer->context;
 if (src_ctx->sock != dst_ctx->sock) {
 return false;
 }
 ggml_backend_rpc_buffer_context * ctx = (ggml_backend_rpc_buffer_context *)buffer->context;
 // input serialization format: | rpc_tensor src | rpc_tensor dst |
 int input_size = 2*sizeof(rpc_tensor);
 std::vector<uint8_t> input(input_size, 0);
 rpc_tensor rpc_src = serialize_tensor(src);
 rpc_tensor rpc_dst = serialize_tensor(dst);
 memcpy(input.data(), &rpc_src, sizeof(rpc_src));
 memcpy(input.data() + sizeof(rpc_src), &rpc_dst, sizeof(rpc_dst));
 std::vector<uint8_t> output;
 bool status = send_rpc_cmd(ctx->sock, COPY_TENSOR, input, output);
 GGML_ASSERT(status);
 // output serialization format: | result (1 byte) |
 GGML_ASSERT(output.size() == 1);
 return output[0];
}

GGML_CALL static void ggml_backend_rpc_buffer_clear(ggml_backend_buffer_t buffer, uint8_t value) {
 ggml_backend_rpc_buffer_context * ctx = (ggml_backend_rpc_buffer_context *)buffer->context;
 // serialization format: | bufptr (8 bytes) | value (1 byte) |
 int input_size = sizeof(uint64_t) + sizeof(uint8_t);
 std::vector<uint8_t> input(input_size, 0);
 memcpy(input.data(), &ctx->remote_ptr, sizeof(ctx->remote_ptr));
 memcpy(input.data() + sizeof(ctx->remote_ptr), &value, sizeof(value));
 std::vector<uint8_t> output;
 bool status = send_rpc_cmd(ctx->sock, BUFFER_CLEAR, input, output);
 GGML_ASSERT(status);
}

static ggml_backend_buffer_i ggml_backend_rpc_buffer_interface = {
 /* .get_name = */ ggml_backend_rpc_buffer_get_name,
 /* .free_buffer = */ ggml_backend_rpc_buffer_free_buffer,
 /* .get_base = */ ggml_backend_rpc_buffer_get_base,
 /* .init_tensor = */ ggml_backend_rpc_buffer_init_tensor,
 /* .set_tensor = */ ggml_backend_rpc_buffer_set_tensor,
 /* .get_tensor = */ ggml_backend_rpc_buffer_get_tensor,
 /* .cpy_tensor = */ ggml_backend_rpc_buffer_cpy_tensor,
 /* .clear = */ ggml_backend_rpc_buffer_clear,
 /* .reset = */ NULL,
};

GGML_CALL static const char * ggml_backend_rpc_buffer_type_name(ggml_backend_buffer_type_t buft) {
 ggml_backend_rpc_buffer_type_context * buft_ctx = (ggml_backend_rpc_buffer_type_context *)buft->context;
 return buft_ctx->name.c_str();
}

GGML_CALL static ggml_backend_buffer_t ggml_backend_rpc_buffer_type_alloc_buffer(ggml_backend_buffer_type_t buft, size_t size) {
 ggml_backend_rpc_buffer_type_context * buft_ctx = (ggml_backend_rpc_buffer_type_context *)buft->context;
 // input serialization format: | size (8 bytes) |
 int input_size = sizeof(uint64_t);
 std::vector<uint8_t> input(input_size, 0);
 memcpy(input.data(), &size, sizeof(size));
 std::vector<uint8_t> output;
 auto sock = get_socket(buft_ctx->endpoint);
 bool status = send_rpc_cmd(sock, ALLOC_BUFFER, input, output);
 GGML_ASSERT(status);
 GGML_ASSERT(output.size() == 2*sizeof(uint64_t));
 // output serialization format: | remote_ptr (8 bytes) | remote_size (8 bytes) |
 uint64_t remote_ptr;
 memcpy(&remote_ptr, output.data(), sizeof(remote_ptr));
 size_t remote_size;
 memcpy(&remote_size, output.data() + sizeof(uint64_t), sizeof(remote_size));
 if (remote_ptr != 0) {
 ggml_backend_buffer_t buffer = ggml_backend_buffer_init(buft,
 ggml_backend_rpc_buffer_interface,
 new ggml_backend_rpc_buffer_context{sock, {}, remote_ptr, "RPC[" + std::string(buft_ctx->endpoint) + "]"},
 remote_size);
 return buffer;
 } else {
 return nullptr;
 }
}

static size_t get_alignment(const std::shared_ptr<socket_t> & sock) {
 // input serialization format: | 0 bytes |
 std::vector<uint8_t> input;
 std::vector<uint8_t> output;
 bool status = send_rpc_cmd(sock, GET_ALIGNMENT, input, output);
 GGML_ASSERT(status);
 GGML_ASSERT(output.size() == sizeof(uint64_t));
 // output serialization format: | alignment (8 bytes) |
 uint64_t alignment;
 memcpy(&alignment, output.data(), sizeof(alignment));
 return alignment;
}

GGML_CALL static size_t ggml_backend_rpc_buffer_type_get_alignment(ggml_backend_buffer_type_t buft) {
 ggml_backend_rpc_buffer_type_context * buft_ctx = (ggml_backend_rpc_buffer_type_context *)buft->context;
 return buft_ctx->alignment;
}

static size_t get_max_size(const std::shared_ptr<socket_t> & sock) {
 // input serialization format: | 0 bytes |
 std::vector<uint8_t> input;
 std::vector<uint8_t> output;
 bool status = send_rpc_cmd(sock, GET_MAX_SIZE, input, output);
 GGML_ASSERT(status);
 GGML_ASSERT(output.size() == sizeof(uint64_t));
 // output serialization format: | max_size (8 bytes) |
 uint64_t max_size;
 memcpy(&max_size, output.data(), sizeof(max_size));
 return max_size;
}

GGML_CALL static size_t ggml_backend_rpc_get_max_size(ggml_backend_buffer_type_t buft) {
 ggml_backend_rpc_buffer_type_context * buft_ctx = (ggml_backend_rpc_buffer_type_context *)buft->context;
 return buft_ctx->max_size;
}

GGML_CALL static size_t ggml_backend_rpc_buffer_type_get_alloc_size(ggml_backend_buffer_type_t buft, const ggml_tensor * tensor) {
 UNUSED(buft);
 return ggml_nbytes(tensor);
}

static ggml_backend_buffer_type_i ggml_backend_rpc_buffer_type_interface = {
 /* .get_name = */ ggml_backend_rpc_buffer_type_name,
 /* .alloc_buffer = */ ggml_backend_rpc_buffer_type_alloc_buffer,
 /* .get_alignment = */ ggml_backend_rpc_buffer_type_get_alignment,
 /* .get_max_size = */ ggml_backend_rpc_get_max_size,
 /* .get_alloc_size = */ ggml_backend_rpc_buffer_type_get_alloc_size,
 /* .is_host = */ NULL,
};

GGML_CALL static const char * ggml_backend_rpc_name(ggml_backend_t backend) {
 ggml_backend_rpc_context * rpc_ctx = (ggml_backend_rpc_context *)backend->context;

 return rpc_ctx->name.c_str();
}

GGML_CALL static void ggml_backend_rpc_free(ggml_backend_t backend) {
 ggml_backend_rpc_context * rpc_ctx = (ggml_backend_rpc_context *)backend->context;
 delete rpc_ctx;
 delete backend;
}

GGML_CALL static ggml_backend_buffer_type_t ggml_backend_rpc_get_default_buffer_type(ggml_backend_t backend) {
 ggml_backend_rpc_context * ctx = (ggml_backend_rpc_context *)backend->context;
 return ggml_backend_rpc_buffer_type(ctx->endpoint.c_str());
}

GGML_CALL static void ggml_backend_rpc_synchronize(ggml_backend_t backend) {
 UNUSED(backend);
 // this is no-op because we don't have any async operations
}

static void add_tensor(ggml_tensor * tensor, std::vector<rpc_tensor> & tensors, std::unordered_set<ggml_tensor*> & visited) {
 if (tensor == nullptr) {
 return;
 }
 if (visited.find(tensor) != visited.end()) {
 return;
 }
 visited.insert(tensor);
 for (int i = 0; i < GGML_MAX_SRC; i++) {
 add_tensor(tensor->src[i], tensors, visited);
 }
 add_tensor(tensor->view_src, tensors, visited);
 tensors.push_back(serialize_tensor(tensor));
}

static void serialize_graph(const ggml_cgraph * cgraph, std::vector<uint8_t> & output) {
 uint32_t n_nodes = cgraph->n_nodes;
 std::vector<rpc_tensor> tensors;
 std::unordered_set<ggml_tensor*> visited;
 for (uint32_t i = 0; i < n_nodes; i++) {
 add_tensor(cgraph->nodes[i], tensors, visited);
 }
 // serialization format:
 // | n_nodes (4 bytes) | nodes (n_nodes * sizeof(uint64_t) | n_tensors (4 bytes) | tensors (n_tensors * sizeof(rpc_tensor)) |
 uint32_t n_tensors = tensors.size();
 int output_size = sizeof(uint32_t) + n_nodes * sizeof(uint64_t) + sizeof(uint32_t) + n_tensors * sizeof(rpc_tensor);
 output.resize(output_size, 0);
 memcpy(output.data(), &n_nodes, sizeof(n_nodes));
 uint64_t * out_nodes = (uint64_t *)(output.data() + sizeof(n_nodes));
 for (uint32_t i = 0; i < n_nodes; i++) {
 out_nodes[i] = reinterpret_cast<uint64_t>(cgraph->nodes[i]);
 }
 uint32_t * out_ntensors = (uint32_t *)(output.data() + sizeof(n_nodes) + n_nodes * sizeof(uint64_t));
 *out_ntensors = n_tensors;
 rpc_tensor * out_tensors = (rpc_tensor *)(output.data() + sizeof(n_nodes) + n_nodes * sizeof(uint64_t) + sizeof(uint32_t));
 memcpy(out_tensors, tensors.data(), n_tensors * sizeof(rpc_tensor));
}

GGML_CALL static enum ggml_status ggml_backend_rpc_graph_compute(ggml_backend_t backend, ggml_cgraph * cgraph) {
 ggml_backend_rpc_context * rpc_ctx = (ggml_backend_rpc_context *)backend->context;
 std::vector<uint8_t> input;
 serialize_graph(cgraph, input);
 std::vector<uint8_t> output;
 auto sock = get_socket(rpc_ctx->endpoint);
 bool status = send_rpc_cmd(sock, GRAPH_COMPUTE, input, output);
 GGML_ASSERT(status);
 GGML_ASSERT(output.size() == 1);
 return (enum ggml_status)output[0];
}

GGML_CALL static bool ggml_backend_rpc_supports_op(ggml_backend_t backend, const ggml_tensor * op) {
 UNUSED(backend);
 UNUSED(op);
 //TODO: call the remote backend and cache the results
 return true;
}

GGML_CALL static bool ggml_backend_rpc_supports_buft(ggml_backend_t backend, ggml_backend_buffer_type_t buft) {
 if (buft->iface.get_name != ggml_backend_rpc_buffer_type_name) {
 return false;
 }
 ggml_backend_rpc_buffer_type_context * buft_ctx = (ggml_backend_rpc_buffer_type_context *)buft->context;
 ggml_backend_rpc_context * rpc_ctx = (ggml_backend_rpc_context *)backend->context;
 return buft_ctx->endpoint == rpc_ctx->endpoint;
}

static ggml_backend_i ggml_backend_rpc_interface = {
 /* .get_name = */ ggml_backend_rpc_name,
 /* .free = */ ggml_backend_rpc_free,
 /* .get_default_buffer_type = */ ggml_backend_rpc_get_default_buffer_type,
 /* .set_tensor_async = */ NULL,
 /* .get_tensor_async = */ NULL,
 /* .cpy_tensor_async = */ NULL,
 /* .synchronize = */ ggml_backend_rpc_synchronize,
 /* .graph_plan_create = */ NULL,
 /* .graph_plan_free = */ NULL,
 /* .graph_plan_update = */ NULL,
 /* .graph_plan_compute = */ NULL,
 /* .graph_compute = */ ggml_backend_rpc_graph_compute,
 /* .supports_op = */ ggml_backend_rpc_supports_op,
 /* .supports_buft = */ ggml_backend_rpc_supports_buft,
 /* .offload_op = */ NULL,
 /* .event_new = */ NULL,
 /* .event_free = */ NULL,
 /* .event_record = */ NULL,
 /* .event_wait = */ NULL,
 /* .event_synchronize = */ NULL,
};

GGML_API GGML_CALL ggml_backend_buffer_type_t ggml_backend_rpc_buffer_type(const char * endpoint) {
 static std::mutex mutex;
 std::lock_guard<std::mutex> lock(mutex);
 // NOTE: buffer types are allocated and never freed; this is by design
 static std::unordered_map<std::string, ggml_backend_buffer_type_t> buft_map;
 auto it = buft_map.find(endpoint);
 if (it != buft_map.end()) {
 return it->second;
 }
 auto sock = get_socket(endpoint);
 if (sock == nullptr) {
 return nullptr;
 }
 size_t alignment = get_alignment(sock);
 size_t max_size = get_max_size(sock);
 ggml_backend_rpc_buffer_type_context * buft_ctx = new ggml_backend_rpc_buffer_type_context {
 /* .endpoint = */ endpoint,
 /* .name = */ "RPC[" + std::string(endpoint) + "]",
 /* .alignment = */ alignment,
 /* .max_size = */ max_size
 };

 ggml_backend_buffer_type_t buft = new ggml_backend_buffer_type {
 /* .iface = */ ggml_backend_rpc_buffer_type_interface,
 /* .context = */ buft_ctx
 };
 buft_map[endpoint] = buft;
 return buft;
}

GGML_CALL ggml_backend_t ggml_backend_rpc_init(const char * endpoint) {
 ggml_backend_rpc_context * ctx = new ggml_backend_rpc_context {
 /* .endpoint = */ endpoint,
 /* .name = */ "RPC[" + std::string(endpoint) + "]",
 };

 ggml_backend_t backend = new ggml_backend {
 /* .guid = */ ggml_backend_rpc_guid(),
 /* .interface = */ ggml_backend_rpc_interface,
 /* .context = */ ctx
 };
 return backend;
}

GGML_API GGML_CALL bool ggml_backend_is_rpc(ggml_backend_t backend) {
 return backend != NULL && ggml_guid_matches(backend->guid, ggml_backend_rpc_guid());
}

static void get_device_memory(const std::shared_ptr<socket_t> & sock, size_t * free, size_t * total) {
 // input serialization format: | 0 bytes |
 std::vector<uint8_t> input;
 std::vector<uint8_t> output;
 bool status = send_rpc_cmd(sock, GET_DEVICE_MEMORY, input, output);
 GGML_ASSERT(status);
 GGML_ASSERT(output.size() == 2*sizeof(uint64_t));
 // output serialization format: | free (8 bytes) | total (8 bytes) |
 uint64_t free_mem;
 memcpy(&free_mem, output.data(), sizeof(free_mem));
 uint64_t total_mem;
 memcpy(&total_mem, output.data() + sizeof(uint64_t), sizeof(total_mem));
 *free = free_mem;
 *total = total_mem;
}

GGML_API GGML_CALL void ggml_backend_rpc_get_device_memory(const char * endpoint, size_t * free, size_t * total) {
 auto sock = get_socket(endpoint);
 if (sock == nullptr) {
 *free = 0;
 *total = 0;
 return;
 }
 get_device_memory(sock, free, total);
}

// RPC server-side implementation

class rpc_server {
public:
 rpc_server(ggml_backend_t backend) : backend(backend) {}
 ~rpc_server();

 bool alloc_buffer(const std::vector<uint8_t> & input, std::vector<uint8_t> & output);
 void get_alignment(std::vector<uint8_t> & output);
 void get_max_size(std::vector<uint8_t> & output);
 bool buffer_get_base(const std::vector<uint8_t> & input, std::vector<uint8_t> & output);
 bool free_buffer(const std::vector<uint8_t> & input);
 bool buffer_clear(const std::vector<uint8_t> & input);
 bool set_tensor(const std::vector<uint8_t> & input);
 bool get_tensor(const std::vector<uint8_t> & input, std::vector<uint8_t> & output);
 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);

private:
 ggml_tensor * deserialize_tensor(struct ggml_context * ctx, const rpc_tensor * tensor);
 ggml_tensor * create_node(uint64_t id,
 struct ggml_context * ctx,
 const std::unordered_map<uint64_t, const rpc_tensor*> & tensor_ptrs,
 std::unordered_map<uint64_t, struct ggml_tensor*> & tensor_map);


 ggml_backend_t backend;
 std::unordered_set<ggml_backend_buffer_t> buffers;
};

bool rpc_server::alloc_buffer(const std::vector<uint8_t> & input, std::vector<uint8_t> & output) {
 // input serialization format: | size (8 bytes) |
 if (input.size() != sizeof(uint64_t)) {
 return false;
 }
 uint64_t size;
 memcpy(&size, input.data(), sizeof(size));
 ggml_backend_buffer_type_t buft = ggml_backend_get_default_buffer_type(backend);
 ggml_backend_buffer_t buffer = ggml_backend_buft_alloc_buffer(buft, size);
 uint64_t remote_ptr = 0;
 uint64_t remote_size = 0;
 if (buffer != nullptr) {
 remote_ptr = reinterpret_cast<uint64_t>(buffer);
 remote_size = buffer->size;
 GGML_PRINT_DEBUG("[%s] size: %" PRIu64 " -> remote_ptr: %" PRIx64 ", remote_size: %" PRIu64 "\n", __func__, size, remote_ptr, remote_size);
 buffers.insert(buffer);
 } else {
 GGML_PRINT_DEBUG("[%s] size: %" PRIu64 " -> failed\n", __func__, size);
 }
 // output serialization format: | remote_ptr (8 bytes) | remote_size (8 bytes) |
 output.resize(2*sizeof(uint64_t), 0);
 memcpy(output.data(), &remote_ptr, sizeof(remote_ptr));
 memcpy(output.data() + sizeof(uint64_t), &remote_size, sizeof(remote_size));
 return true;
}

void rpc_server::get_alignment(std::vector<uint8_t> & output) {
 ggml_backend_buffer_type_t buft = ggml_backend_get_default_buffer_type(backend);
 size_t alignment = ggml_backend_buft_get_alignment(buft);
 GGML_PRINT_DEBUG("[%s] alignment: %lu\n", __func__, alignment);
 // output serialization format: | alignment (8 bytes) |
 output.resize(sizeof(uint64_t), 0);
 memcpy(output.data(), &alignment, sizeof(alignment));
}

void rpc_server::get_max_size(std::vector<uint8_t> & output) {
 ggml_backend_buffer_type_t buft = ggml_backend_get_default_buffer_type(backend);
 size_t max_size = ggml_backend_buft_get_max_size(buft);
 GGML_PRINT_DEBUG("[%s] max_size: %lu\n", __func__, max_size);
 // output serialization format: | max_size (8 bytes) |
 output.resize(sizeof(uint64_t), 0);
 memcpy(output.data(), &max_size, sizeof(max_size));
}

bool rpc_server::buffer_get_base(const std::vector<uint8_t> & input, std::vector<uint8_t> & output) {
 // input serialization format: | remote_ptr (8 bytes) |
 if (input.size() != sizeof(uint64_t)) {
 return false;
 }
 uint64_t remote_ptr;
 memcpy(&remote_ptr, input.data(), sizeof(remote_ptr));
 GGML_PRINT_DEBUG("[%s] remote_ptr: %" PRIx64 "\n", __func__, remote_ptr);
 ggml_backend_buffer_t buffer = reinterpret_cast<ggml_backend_buffer_t>(remote_ptr);
 if (buffers.find(buffer) == buffers.end()) {
 GGML_PRINT_DEBUG("[%s] buffer not found\n", __func__);
 return false;
 }
 void * base = ggml_backend_buffer_get_base(buffer);
 // output serialization format: | base_ptr (8 bytes) |
 uint64_t base_ptr = reinterpret_cast<uint64_t>(base);
 output.resize(sizeof(uint64_t), 0);
 memcpy(output.data(), &base_ptr, sizeof(base_ptr));
 return true;
}

bool rpc_server::free_buffer(const std::vector<uint8_t> & input) {
 // input serialization format: | remote_ptr (8 bytes) |
 if (input.size() != sizeof(uint64_t)) {
 return false;
 }
 uint64_t remote_ptr;
 memcpy(&remote_ptr, input.data(), sizeof(remote_ptr));
 GGML_PRINT_DEBUG("[%s] remote_ptr: %" PRIx64 "\n", __func__, remote_ptr);
 ggml_backend_buffer_t buffer = reinterpret_cast<ggml_backend_buffer_t>(remote_ptr);
 if (buffers.find(buffer) == buffers.end()) {
 GGML_PRINT_DEBUG("[%s] buffer not found\n", __func__);
 return false;
 }
 ggml_backend_buffer_free(buffer);
 buffers.erase(buffer);
 return true;
}

bool rpc_server::buffer_clear(const std::vector<uint8_t> & input) {
 // input serialization format: | remote_ptr (8 bytes) | value (1 byte) |
 if (input.size() != sizeof(uint64_t) + sizeof(uint8_t)) {
 return false;
 }
 uint64_t remote_ptr;
 memcpy(&remote_ptr, input.data(), sizeof(remote_ptr));
 uint8_t value;
 memcpy(&value, input.data() + sizeof(uint64_t), sizeof(value));
 GGML_PRINT_DEBUG("[%s] remote_ptr: %" PRIx64 ", value: %u\n", __func__, remote_ptr, value);
 ggml_backend_buffer_t buffer = reinterpret_cast<ggml_backend_buffer_t>(remote_ptr);
 if (buffers.find(buffer) == buffers.end()) {
 GGML_PRINT_DEBUG("[%s] buffer not found\n", __func__);
 return false;
 }
 ggml_backend_buffer_clear(buffer, value);
 return true;
}

ggml_tensor * rpc_server::deserialize_tensor(struct ggml_context * ctx, const rpc_tensor * tensor) {
 ggml_tensor * result = ggml_new_tensor_4d(ctx, (ggml_type) tensor->type,
 tensor->ne[0], tensor->ne[1], tensor->ne[2], tensor->ne[3]);
 for (uint32_t i = 0; i < GGML_MAX_DIMS; i++) {
 result->nb[i] = tensor->nb[i];
 }
 result->buffer = reinterpret_cast<ggml_backend_buffer_t>(tensor->buffer);
 if (result->buffer && buffers.find(result->buffer) == buffers.end()) {
 return nullptr;
 }
 result->op = (ggml_op) tensor->op;
 for (uint32_t i = 0; i < GGML_MAX_OP_PARAMS / sizeof(int32_t); i++) {
 result->op_params[i] = tensor->op_params[i];
 }
 result->flags = tensor->flags;
 result->data = reinterpret_cast<void *>(tensor->data);
 ggml_set_name(result, tensor->name);
 return result;
}


bool rpc_server::set_tensor(const std::vector<uint8_t> & input) {
 // serialization format: | rpc_tensor | offset (8 bytes) | data (size bytes) |
 if (input.size() < sizeof(rpc_tensor) + sizeof(uint64_t)) {
 return false;
 }
 const rpc_tensor * in_tensor = (const rpc_tensor *)input.data();
 uint64_t offset;
 memcpy(&offset, input.data() + sizeof(rpc_tensor), sizeof(offset));
 size_t size = input.size() - sizeof(rpc_tensor) - sizeof(offset);

 struct ggml_init_params params {
 /*.mem_size =*/ ggml_tensor_overhead(),
 /*.mem_buffer =*/ NULL,
 /*.no_alloc =*/ true,
 };
 struct ggml_context * ctx = ggml_init(params);
 ggml_tensor * tensor = deserialize_tensor(ctx, in_tensor);
 if (tensor == nullptr) {
 GGML_PRINT_DEBUG("[%s] error deserializing tensor\n", __func__);
 ggml_free(ctx);
 return false;
 }
 GGML_PRINT_DEBUG("[%s] buffer: %p, data: %p, offset: %" PRIu64 ", size: %zu\n", __func__, (void*)tensor->buffer, tensor->data, offset, size);
 const void * data = input.data() + sizeof(rpc_tensor) + sizeof(offset);
 ggml_backend_tensor_set(tensor, data, offset, size);
 ggml_free(ctx);
 return true;
}

bool rpc_server::get_tensor(const std::vector<uint8_t> & input, std::vector<uint8_t> & output) {
 // serialization format: | rpc_tensor | offset (8 bytes) | size (8 bytes) |
 if (input.size() != sizeof(rpc_tensor) + 2*sizeof(uint64_t)) {
 return false;
 }
 const rpc_tensor * in_tensor = (const rpc_tensor *)input.data();
 uint64_t offset;
 memcpy(&offset, input.data() + sizeof(rpc_tensor), sizeof(offset));
 uint64_t size;
 memcpy(&size, input.data() + sizeof(rpc_tensor) + sizeof(offset), sizeof(size));

 struct ggml_init_params params {
 /*.mem_size =*/ ggml_tensor_overhead(),
 /*.mem_buffer =*/ NULL,
 /*.no_alloc =*/ true,
 };
 struct ggml_context * ctx = ggml_init(params);
 ggml_tensor * tensor = deserialize_tensor(ctx, in_tensor);
 if (tensor == nullptr) {
 GGML_PRINT_DEBUG("[%s] error deserializing tensor\n", __func__);
 ggml_free(ctx);
 return false;
 }
 GGML_PRINT_DEBUG("[%s] buffer: %p, data: %p, offset: %" PRIu64 ", size: %" PRIu64 "\n", __func__, (void*)tensor->buffer, tensor->data, offset, size);
 // output serialization format: | data (size bytes) |
 output.resize(size, 0);
 ggml_backend_tensor_get(tensor, output.data(), offset, size);
 ggml_free(ctx);
 return true;
}

bool rpc_server::copy_tensor(const std::vector<uint8_t> & input, std::vector<uint8_t> & output) {
 // serialization format: | rpc_tensor src | rpc_tensor dst |
 if (input.size() != 2*sizeof(rpc_tensor)) {
 return false;
 }
 const rpc_tensor * rpc_src = (const rpc_tensor *)input.data();
 const rpc_tensor * rpc_dst = (const rpc_tensor *)(input.data() + sizeof(rpc_src));

 struct ggml_init_params params {
 /*.mem_size =*/ 2*ggml_tensor_overhead(),
 /*.mem_buffer =*/ NULL,
 /*.no_alloc =*/ true,
 };
 struct ggml_context * ctx = ggml_init(params);
 ggml_tensor * src = deserialize_tensor(ctx, rpc_src);
 ggml_tensor * dst = deserialize_tensor(ctx, rpc_dst);
 if (src == nullptr || dst == nullptr) {
 GGML_PRINT_DEBUG("[%s] error deserializing tensors\n", __func__);
 ggml_free(ctx);
 return false;
 }
 GGML_PRINT_DEBUG("[%s] src->buffer: %p, dst->buffer: %p\n", __func__, (void*)src->buffer, (void*)dst->buffer);
 bool result = ggml_backend_buffer_copy_tensor(src, dst);
 // output serialization format: | result (1 byte) |
 output.resize(1, 0);
 output[0] = result;
 ggml_free(ctx);
 return true;
}

ggml_tensor * rpc_server::create_node(uint64_t id,
 struct ggml_context * ctx,
 const std::unordered_map<uint64_t, const rpc_tensor*> & tensor_ptrs,
 std::unordered_map<uint64_t, struct ggml_tensor*> & tensor_map) {
 if (id == 0) {
 return nullptr;
 }
 if (tensor_map.find(id) != tensor_map.end()) {
 return tensor_map[id];
 }
 const rpc_tensor * tensor = tensor_ptrs.at(id);
 struct ggml_tensor * result = deserialize_tensor(ctx, tensor);
 if (result == nullptr) {
 return nullptr;
 }
 tensor_map[id] = result;
 for (int i = 0; i < GGML_MAX_SRC; i++) {
 result->src[i] = create_node(tensor->src[i], ctx, tensor_ptrs, tensor_map);
 }
 result->view_src = create_node(tensor->view_src, ctx, tensor_ptrs, tensor_map);
 result->view_offs = tensor->view_offs;
 return result;
}

bool rpc_server::graph_compute(const std::vector<uint8_t> & input, std::vector<uint8_t> & output) {
 // serialization format:
 // | n_nodes (4 bytes) | nodes (n_nodes * sizeof(uint64_t) | n_tensors (4 bytes) | tensors (n_tensors * sizeof(rpc_tensor)) |
 if (input.size() < sizeof(uint32_t)) {
 return false;
 }
 uint32_t n_nodes;
 memcpy(&n_nodes, input.data(), sizeof(n_nodes));
 if (input.size() < sizeof(uint32_t) + n_nodes*sizeof(uint64_t) + sizeof(uint32_t)) {
 return false;
 }
 const uint64_t * nodes = (const uint64_t *)(input.data() + sizeof(n_nodes));
 uint32_t n_tensors;
 memcpy(&n_tensors, input.data() + sizeof(n_nodes) + n_nodes*sizeof(uint64_t), sizeof(n_tensors));
 if (input.size() < sizeof(uint32_t) + n_nodes*sizeof(uint64_t) + sizeof(uint32_t) + n_tensors*sizeof(rpc_tensor)) {
 return false;
 }
 const rpc_tensor * tensors = (const rpc_tensor *)(input.data() + sizeof(n_nodes) + n_nodes*sizeof(uint64_t) + sizeof(n_tensors));
 GGML_PRINT_DEBUG("[%s] n_nodes: %u, n_tensors: %u\n", __func__, n_nodes, n_tensors);

 static size_t buf_size = ggml_tensor_overhead()*(n_nodes + n_tensors) + ggml_graph_overhead_custom(n_nodes, false);
 struct ggml_init_params params = {
 /*.mem_size =*/ buf_size,
 /*.mem_buffer =*/ NULL,
 /*.no_alloc =*/ true,
 };
 struct ggml_context * ctx = ggml_init(params);
 struct ggml_cgraph * graph = ggml_new_graph_custom(ctx, n_nodes, false);
 graph->n_nodes = n_nodes;
 std::unordered_map<uint64_t, const rpc_tensor*> tensor_ptrs;
 for (uint32_t i = 0; i < n_tensors; i++) {
 tensor_ptrs[tensors[i].id] = &tensors[i];
 }
 std::unordered_map<uint64_t, ggml_tensor*> tensor_map;
 for (uint32_t i = 0; i < n_nodes; i++) {
 graph->nodes[i] = create_node(nodes[i], ctx, tensor_ptrs, tensor_map);
 }
 ggml_status status = ggml_backend_graph_compute(backend, graph);
 // output serialization format: | status (1 byte) |
 output.resize(1, 0);
 output[0] = status;
 ggml_free(ctx);
 return true;
}

rpc_server::~rpc_server() {
 for (auto buffer : buffers) {
 ggml_backend_buffer_free(buffer);
 }
}

static void rpc_serve_client(ggml_backend_t backend, sockfd_t sockfd, size_t free_mem, size_t total_mem) {
 rpc_server server(backend);
 while (true) {
 uint8_t cmd;
 if (!recv_data(sockfd, &cmd, 1)) {
 break;
 }
 std::vector<uint8_t> input;
 std::vector<uint8_t> output;
 uint64_t input_size;
 if (!recv_data(sockfd, &input_size, sizeof(input_size))) {
 break;
 }
 input.resize(input_size);
 if (!recv_data(sockfd, input.data(), input_size)) {
 break;
 }
 bool ok = true;
 switch (cmd) {
 case ALLOC_BUFFER: {
 ok = server.alloc_buffer(input, output);
 break;
 }
 case GET_ALIGNMENT: {
 server.get_alignment(output);
 break;
 }
 case GET_MAX_SIZE: {
 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);
 break;
 }
 case GET_DEVICE_MEMORY: {
 // output serialization format: | free (8 bytes) | total (8 bytes) |
 output.resize(2*sizeof(uint64_t), 0);
 memcpy(output.data(), &free_mem, sizeof(free_mem));
 memcpy(output.data() + sizeof(uint64_t), &total_mem, sizeof(total_mem));
 break;
 }
 default: {
 fprintf(stderr, "Unknown command: %d\n", cmd);
 ok = false;
 }
 }
 if (!ok) {
 break;
 }
 uint64_t output_size = output.size();
 if (!send_data(sockfd, &output_size, sizeof(output_size))) {
 break;
 }
 if (!send_data(sockfd, output.data(), output_size)) {
 break;
 }
 }
}

void start_rpc_server(ggml_backend_t backend, const char * endpoint, size_t free_mem, size_t total_mem) {
 std::string host;
 int port;
 if (!parse_endpoint(endpoint, host, port)) {
 return;
 }
#ifdef _WIN32
 {
 WSADATA wsaData;
 int res = WSAStartup(MAKEWORD(2, 2), &wsaData);
 if (res != 0) {
 fprintf(stderr, "WSAStartup failed: %d\n", res);
 return;
 }
 }
#endif
 auto server_socket = create_server_socket(host.c_str(), port);
 if (server_socket == nullptr) {
 fprintf(stderr, "Failed to create server socket\n");
 return;
 }
 while (true) {
 auto client_socket = socket_accept(server_socket->fd);
 if (client_socket == nullptr) {
 fprintf(stderr, "Failed to accept client connection\n");
 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);
 printf("Client connection closed\n");
 }
#ifdef _WIN32
 WSACleanup();
#endif
}