Refactoring launcher

CMakeLists.txt

@@ -119,6 +119,10 @@ if(MLX_BUILD_METAL)
     COMMAND zsh "-c" "/usr/bin/xcrun -sdk macosx --show-sdk-version"
     OUTPUT_VARIABLE MACOS_SDK_VERSION
     OUTPUT_STRIP_TRAILING_WHITESPACE COMMAND_ERROR_IS_FATAL ANY)
+  execute_process(
+    COMMAND zsh "-c" "/usr/bin/xcrun -sdk macosx --show-sdk-path"
+    OUTPUT_VARIABLE CMAKE_OSX_SYSROOT
+    OUTPUT_STRIP_TRAILING_WHITESPACE COMMAND_ERROR_IS_FATAL ANY)
 
   if(${MACOS_SDK_VERSION} LESS 14.0)
     message(

mlx/distributed/CMakeLists.txt

@@ -4,6 +4,11 @@ target_sources(
           ${CMAKE_CURRENT_SOURCE_DIR}/ops.cpp
           ${CMAKE_CURRENT_SOURCE_DIR}/distributed.cpp)
 
+if(MLX_BUILD_CPU AND NOT WIN32)
+  target_sources(mlx PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/utils.cpp)
+endif()
+
 add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/mpi)
 add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/ring)
 add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/nccl)
+add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/jaccl)

mlx/distributed/distributed.cpp

@@ -5,6 +5,7 @@
 #include "mlx/backend/cuda/cuda.h"
 #include "mlx/distributed/distributed.h"
 #include "mlx/distributed/distributed_impl.h"
+#include "mlx/distributed/jaccl/jaccl.h"
 #include "mlx/distributed/mpi/mpi.h"
 #include "mlx/distributed/nccl/nccl.h"
 #include "mlx/distributed/ring/ring.h"
@@ -102,7 +103,27 @@ class EmptyGroup : public GroupImpl {
 } // namespace detail
 
 bool is_available() {
-  return mpi::is_available() || ring::is_available() || nccl::is_available();
+  return mpi::is_available() || ring::is_available() || nccl::is_available() ||
+      jaccl::is_available();
+}
+
+bool is_available(const std::string& bk) {
+  if (bk == "any") {
+    return is_available();
+  }
+  if (bk == "mpi") {
+    return mpi::is_available();
+  }
+  if (bk == "ring") {
+    return ring::is_available();
+  }
+  if (bk == "nccl") {
+    return nccl::is_available();
+  }
+  if (bk == "jaccl") {
+    return jaccl::is_available();
+  }
+  return false;
 }
 
 int Group::rank() const {
@@ -135,6 +156,8 @@ Group init(bool strict /* = false */, const std::string& bk /* = "any" */) {
     group = ring::init(strict);
   } else if (bk == "nccl") {
     group = nccl::init(strict);
+  } else if (bk == "jaccl") {
+    group = jaccl::init(strict);
   } else if (bk == "any") {
     if (mlx::core::cu::is_available()) {
       group = nccl::init(false);
@@ -148,13 +171,17 @@ Group init(bool strict /* = false */, const std::string& bk /* = "any" */) {
       group = mpi::init(false);
       bk_ = "mpi";
     }
+    if (group == nullptr) {
+      group = jaccl::init(false);
+      bk_ = "jaccl";
+    }
     if (group == nullptr && strict) {
       throw std::runtime_error("[distributed] Couldn't initialize any backend");
     }
   } else {
     std::ostringstream msg;
-    msg << "[distributed] The only valid values for backend are 'any', 'mpi' "
-        << "and 'ring' but '" << bk << "' was provided.";
+    msg << "[distributed] The only valid values for backend are 'any', 'mpi', 'nccl', "
+        << "'jaccl' and 'ring' but '" << bk << "' was provided.";
     throw std::invalid_argument(msg.str());
   }
 

mlx/distributed/distributed.h

@@ -16,6 +16,7 @@ class GroupImpl;
 
 /* Check if a communication backend is available */
 bool is_available();
+bool is_available(const std::string& bk);
 
 /**
  * A distributed::Group represents a group of independent mlx processes that

mlx/distributed/jaccl/CMakeLists.txt

@@ -0,0 +1,8 @@
+if(MLX_BUILD_CPU
+   AND ${CMAKE_SYSTEM_NAME} MATCHES "Darwin"
+   AND MACOS_SDK_VERSION GREATER_EQUAL 26.2)
+  target_sources(mlx PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/jaccl.cpp)
+  target_link_libraries(mlx PRIVATE rdma)
+else()
+  target_sources(mlx PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/no_jaccl.cpp)
+endif()

mlx/distributed/jaccl/jaccl.h

@@ -0,0 +1,12 @@
+// Copyright © 2025 Apple Inc.
+
+#include "mlx/distributed/distributed.h"
+
+namespace mlx::core::distributed::jaccl {
+
+using GroupImpl = mlx::core::distributed::detail::GroupImpl;
+
+bool is_available();
+std::shared_ptr<GroupImpl> init(bool strict = false);
+
+} // namespace mlx::core::distributed::jaccl

mlx/distributed/jaccl/no_jaccl.cpp

@@ -0,0 +1,20 @@
+// Copyright © 2025 Apple Inc.
+
+#include "mlx/distributed/jaccl/jaccl.h"
+
+namespace mlx::core::distributed::jaccl {
+
+using GroupImpl = mlx::core::distributed::detail::GroupImpl;
+
+bool is_available() {
+  return false;
+}
+
+std::shared_ptr<GroupImpl> init(bool strict /* = false */) {
+  if (strict) {
+    throw std::runtime_error("Cannot initialize jaccl distributed backend.");
+  }
+  return nullptr;
+}
+
+} // namespace mlx::core::distributed::jaccl

mlx/distributed/reduction_ops.h

@@ -0,0 +1,38 @@
+// Copyright © 2025 Apple Inc.
+
+namespace mlx::core::distributed::detail {
+
+template <typename T>
+struct SumOp {
+  void operator()(const T* input, T* output, size_t N) const {
+    while (N-- > 0) {
+      *output += *input;
+      input++;
+      output++;
+    }
+  }
+};
+
+template <typename T>
+struct MaxOp {
+  void operator()(const T* input, T* output, size_t N) const {
+    while (N-- > 0) {
+      *output = std::max(*output, *input);
+      input++;
+      output++;
+    }
+  }
+};
+
+template <typename T>
+struct MinOp {
+  void operator()(const T* input, T* output, size_t N) const {
+    while (N-- > 0) {
+      *output = std::min(*output, *input);
+      input++;
+      output++;
+    }
+  }
+};
+
+} // namespace mlx::core::distributed::detail

mlx/distributed/ring/ring.cpp

@@ -1,9 +1,6 @@
 // Copyright © 2024 Apple Inc.
 
-#include <arpa/inet.h>
 #include <fcntl.h>
-#include <netdb.h>
-#include <netinet/in.h>
 #include <netinet/tcp.h>
 #include <sys/socket.h>
 #include <unistd.h>
@@ -22,6 +19,8 @@
 #include "mlx/backend/cpu/encoder.h"
 #include "mlx/distributed/distributed.h"
 #include "mlx/distributed/distributed_impl.h"
+#include "mlx/distributed/reduction_ops.h"
+#include "mlx/distributed/utils.h"
 #include "mlx/threadpool.h"
 
 #ifndef SOL_TCP
@@ -94,6 +93,7 @@ constexpr const size_t ALL_SUM_SIZE = 8 * 1024 * 1024;
 constexpr const size_t ALL_SUM_BUFFERS = 2;
 constexpr const int CONN_ATTEMPTS = 5;
 constexpr const int CONN_WAIT = 1000;
+constexpr const char* RING_TAG = "[ring]";
 
 using GroupImpl = mlx::core::distributed::detail::GroupImpl;
 using json = nlohmann::json;
@@ -296,55 +296,6 @@ class CommunicationThreads {
   std::unordered_map<int, SocketThread> threads_;
 };
 
-struct address_t {
-  sockaddr_storage addr;
-  socklen_t len;
-
-  const sockaddr* get() const {
-    return (struct sockaddr*)&addr;
-  }
-};
-
-/**
- * Parse a sockaddr from an ip and port provided as strings.
- */
-address_t parse_address(const std::string& ip, const std::string& port) {
-  struct addrinfo hints, *res;
-  memset(&hints, 0, sizeof(hints));
-  hints.ai_family = AF_UNSPEC;
-  hints.ai_socktype = SOCK_STREAM;
-
-  int status = getaddrinfo(ip.c_str(), port.c_str(), &hints, &res);
-  if (status != 0) {
-    std::ostringstream msg;
-    msg << "Can't parse address " << ip << ":" << port;
-    throw std::runtime_error(msg.str());
-  }
-
-  address_t result;
-  memcpy(&result.addr, res->ai_addr, res->ai_addrlen);
-  result.len = res->ai_addrlen;
-  freeaddrinfo(res);
-
-  return result;
-}
-
-/**
- * Parse a sockaddr provided as an <ip>:<port> string.
- */
-address_t parse_address(const std::string& ip_port) {
-  auto colon = ip_port.find(":");
-  if (colon == std::string::npos) {
-    std::ostringstream msg;
-    msg << "Can't parse address " << ip_port;
-    throw std::runtime_error(msg.str());
-  }
-  std::string ip(ip_port.begin(), ip_port.begin() + colon);
-  std::string port(ip_port.begin() + colon + 1, ip_port.end());
-
-  return parse_address(ip, port);
-}
-
 /**
  * Load all addresses from the json hostfile. The hostfile is a list of
  * addresses in order of rank. For each rank there can be many addresses so
@@ -357,15 +308,15 @@ address_t parse_address(const std::string& ip_port) {
  *    ["ip3:5000", "ip3:5001"],
  *  ]
  */
-std::vector<std::vector<address_t>> load_nodes(const char* hostfile) {
-  std::vector<std::vector<address_t>> nodes;
+std::vector<std::vector<detail::address_t>> load_nodes(const char* hostfile) {
+  std::vector<std::vector<detail::address_t>> nodes;
   std::ifstream f(hostfile);
 
   json hosts = json::parse(f);
   for (auto& h : hosts) {
-    std::vector<address_t> host;
+    std::vector<detail::address_t> host;
     for (auto& ips : h) {
-      host.push_back(parse_address(ips.get<std::string>()));
+      host.push_back(std::move(detail::parse_address(ips.get<std::string>())));
     }
     nodes.push_back(std::move(host));
   }
@@ -377,73 +328,15 @@ std::vector<std::vector<address_t>> load_nodes(const char* hostfile) {
  * Create a socket and accept one connection for each of the provided
  * addresses.
  */
-std::vector<int> accept_connections(const std::vector<address_t>& addresses) {
+std::vector<int> accept_connections(
+    const std::vector<detail::address_t>& addresses) {
   std::vector<int> sockets;
   int success;
 
   for (auto& address : addresses) {
-    // Create the socket to wait for connections from the peers
-    int sock = socket(AF_INET, SOCK_STREAM, 0);
-    if (sock < 0) {
-      std::ostringstream msg;
-      msg << "[ring] Couldn't create socket (error: " << errno << ")";
-      throw std::runtime_error(msg.str());
-    }
-
-    // Make sure we can launch immediately after shutdown by setting the
-    // reuseaddr option so that we don't get address already in use errors
-    int enable = 1;
-    success = setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &enable, sizeof(int));
-    if (success < 0) {
-      shutdown(sock, 2);
-      close(sock);
-      std::ostringstream msg;
-      msg << "[ring] Couldn't enable reuseaddr (error: " << errno << ")";
-      throw std::runtime_error(msg.str());
-    }
-    success = setsockopt(sock, SOL_SOCKET, SO_REUSEPORT, &enable, sizeof(int));
-    if (success < 0) {
-      shutdown(sock, 2);
-      close(sock);
-      std::ostringstream msg;
-      msg << "[ring] Couldn't enable reuseport (error: " << errno << ")";
-      throw std::runtime_error(msg.str());
-    }
-
-    // Bind the socket to the address and port
-    success = bind(sock, address.get(), address.len);
-    if (success < 0) {
-      shutdown(sock, 2);
-      close(sock);
-      std::ostringstream msg;
-      msg << "[ring] Couldn't bind socket (error: " << errno << ")";
-      throw std::runtime_error(msg.str());
-    }
-
-    // Wait for connections
-    success = listen(sock, 0);
-    if (success < 0) {
-      shutdown(sock, 2);
-      close(sock);
-      std::ostringstream msg;
-      msg << "[ring] Couldn't listen (error: " << errno << ")";
-      throw std::runtime_error(msg.str());
-    }
-
-    int peer_socket = accept(sock, nullptr, nullptr);
-    if (peer_socket < 0) {
-      shutdown(sock, 2);
-      close(sock);
-      std::ostringstream msg;
-      msg << "[ring] Accept failed (error: " << errno << ")";
-      throw std::runtime_error(msg.str());
-    }
-
-    // Close the listening socket
-    shutdown(sock, 2);
-    close(sock);
-
-    sockets.push_back(peer_socket);
+    detail::TCPSocket socket(RING_TAG);
+    socket.listen(RING_TAG, address);
+    sockets.push_back(socket.accept(RING_TAG).detach());
   }
 
   return sockets;
@@ -454,93 +347,42 @@ std::vector<int> accept_connections(const std::vector<address_t>& addresses) {
  * provided addresses.
  */
 std::vector<int> make_connections(
-    const std::vector<address_t>& addresses,
+    const std::vector<detail::address_t>& addresses,
     bool verbose) {
   std::vector<int> sockets;
   int success;
 
   for (auto& address : addresses) {
-    int sock;
-
-    // Attempt to connect to the peer CONN_ATTEMPTS times with exponential
-    // backoff. TODO: Do we need that?
-    for (int attempt = 0; attempt < CONN_ATTEMPTS; attempt++) {
-      // Create the socket
-      sock = socket(AF_INET, SOCK_STREAM, 0);
-      if (sock < 0) {
-        std::ostringstream msg;
-        msg << "[ring] Couldn't create socket (error: " << errno << ")";
-        throw std::runtime_error(msg.str());
-      }
-
-      if (attempt > 0) {
-        int wait = (1 << (attempt - 1)) * CONN_WAIT;
-        log_info(
-            verbose,
-            "Attempt",
-            attempt,
-            "wait",
-            wait,
-            "ms (error:",
-            errno,
-            ")");
-        std::this_thread::sleep_for(std::chrono::milliseconds(wait));
-      }
-
-      success = connect(sock, address.get(), address.len);
-      if (success == 0) {
-        break;
-      }
-    }
-    if (success < 0) {
-      std::ostringstream msg;
-      msg << "[ring] Couldn't connect (error: " << errno << ")";
-      throw std::runtime_error(msg.str());
-    }
-
-    sockets.push_back(sock);
+    sockets.push_back(detail::TCPSocket::connect(
+                          RING_TAG,
+                          address,
+                          CONN_ATTEMPTS,
+                          CONN_WAIT,
+                          [verbose](int attempt, int wait) {
+                            log_info(
+                                verbose,
+                                "Attempt",
+                                attempt,
+                                "waiting",
+                                wait,
+                                "ms (error:",
+                                errno,
+                                ")");
+                          })
+                          .detach());
   }
 
   return sockets;
 }
-template <typename T>
-struct SumOp {
-  void operator()(const T* input, T* output, size_t N) {
-    while (N-- > 0) {
-      *output += *input;
-      input++;
-      output++;
-    }
-  }
-};
-
-template <typename T>
-struct MaxOp {
-  void operator()(const T* input, T* output, size_t N) {
-    while (N-- > 0) {
-      *output = std::max(*output, *input);
-      input++;
-      output++;
-    }
-  }
-};
-
-template <typename T>
-struct MinOp {
-  void operator()(const T* input, T* output, size_t N) {
-    while (N-- > 0) {
-      *output = std::min(*output, *input);
-      input++;
-      output++;
-    }
-  }
-};
 
 } // namespace
 
 class RingGroup : public GroupImpl {
  public:
-  RingGroup(int rank, std::vector<std::vector<address_t>> nodes, bool verbose)
+  RingGroup(
+      int rank,
+      std::vector<std::vector<detail::address_t>> nodes,
+      bool verbose)
       : rank_(rank), verbose_(verbose), pool_(0) {
     if (rank_ > 0 && rank_ >= nodes.size()) {
       throw std::runtime_error(
@@ -633,17 +475,17 @@ class RingGroup : public GroupImpl {
 
   void all_sum(const array& input, array& output, Stream stream) override {
     SWITCH_TYPE(
-        output, all_reduce<T, SumOp<T>>(input, output, stream, SumOp<T>()));
+        output, all_reduce<T>(input, output, stream, detail::SumOp<T>()));
   }
 
   void all_max(const array& input, array& output, Stream stream) override {
     SWITCH_TYPE(
-        output, all_reduce<T, MaxOp<T>>(input, output, stream, MaxOp<T>()));
+        output, all_reduce<T>(input, output, stream, detail::MaxOp<T>()));
   }
 
   void all_min(const array& input, array& output, Stream stream) override {
     SWITCH_TYPE(
-        output, all_reduce<T, MinOp<T>>(input, output, stream, MinOp<T>()));
+        output, all_reduce<T>(input, output, stream, detail::MinOp<T>()));
   }
 
   std::shared_ptr<GroupImpl> split(int color, int key = -1) override {

mlx/distributed/utils.cpp

@@ -0,0 +1,204 @@
+// Copyright © 2025 Apple Inc.
+
+#include <netdb.h>
+#include <unistd.h>
+#include <cstring>
+#include <sstream>
+#include <thread>
+
+#include "mlx/distributed/utils.h"
+
+namespace mlx::core::distributed::detail {
+
+/**
+ * Parse a sockaddr from an ip and port provided as strings.
+ */
+address_t parse_address(const std::string& ip, const std::string& port) {
+  struct addrinfo hints, *res;
+  std::memset(&hints, 0, sizeof(hints));
+  hints.ai_family = AF_UNSPEC;
+  hints.ai_socktype = SOCK_STREAM;
+
+  int status = getaddrinfo(ip.c_str(), port.c_str(), &hints, &res);
+  if (status != 0) {
+    std::ostringstream msg;
+    msg << "Can't parse address " << ip << ":" << port;
+    throw std::runtime_error(msg.str());
+  }
+
+  address_t result;
+  memcpy(&result.addr, res->ai_addr, res->ai_addrlen);
+  result.len = res->ai_addrlen;
+  freeaddrinfo(res);
+
+  return result;
+}
+
+/**
+ * Parse a sockaddr provided as an <ip>:<port> string.
+ */
+address_t parse_address(const std::string& ip_port) {
+  auto colon = ip_port.find(":");
+  if (colon == std::string::npos) {
+    std::ostringstream msg;
+    msg << "Can't parse address " << ip_port;
+    throw std::runtime_error(msg.str());
+  }
+  std::string ip(ip_port.begin(), ip_port.begin() + colon);
+  std::string port(ip_port.begin() + colon + 1, ip_port.end());
+
+  return parse_address(ip, port);
+}
+
+TCPSocket::TCPSocket(const char* tag) {
+  sock_ = socket(AF_INET, SOCK_STREAM, 0);
+  if (sock_ < 0) {
+    std::ostringstream msg;
+    msg << tag << " Couldn't create socket (error: " << errno << ")";
+    throw std::runtime_error(msg.str());
+  }
+}
+
+TCPSocket::TCPSocket(TCPSocket&& s) {
+  sock_ = s.sock_;
+  s.sock_ = -1;
+}
+
+TCPSocket& TCPSocket::operator=(TCPSocket&& s) {
+  if (this != &s) {
+    sock_ = s.sock_;
+    s.sock_ = -1;
+  }
+  return *this;
+}
+
+TCPSocket::TCPSocket(int s) : sock_(s) {}
+
+TCPSocket::~TCPSocket() {
+  if (sock_ > 0) {
+    shutdown(sock_, 2);
+    close(sock_);
+  }
+}
+
+int TCPSocket::detach() {
+  int s = sock_;
+  sock_ = -1;
+  return s;
+}
+
+void TCPSocket::listen(const char* tag, const address_t& addr) {
+  int success;
+
+  // Make sure we can launch immediately after shutdown by setting the
+  // reuseaddr option so that we don't get address already in use errors
+  int enable = 1;
+  success = setsockopt(sock_, SOL_SOCKET, SO_REUSEADDR, &enable, sizeof(int));
+  if (success < 0) {
+    std::ostringstream msg;
+    msg << tag << " Couldn't enable reuseaddr (error: " << errno << ")";
+    throw std::runtime_error(msg.str());
+  }
+  success = setsockopt(sock_, SOL_SOCKET, SO_REUSEPORT, &enable, sizeof(int));
+  if (success < 0) {
+    std::ostringstream msg;
+    msg << tag << " Couldn't enable reuseport (error: " << errno << ")";
+    throw std::runtime_error(msg.str());
+  }
+
+  // Bind the socket to the address and port
+  success = bind(sock_, addr.get(), addr.len);
+  if (success < 0) {
+    std::ostringstream msg;
+    msg << tag << " Couldn't bind socket (error: " << errno << ")";
+    throw std::runtime_error(msg.str());
+  }
+
+  // Prepare waiting for connections
+  success = ::listen(sock_, 0);
+  if (success < 0) {
+    std::ostringstream msg;
+    msg << tag << " Couldn't listen (error: " << errno << ")";
+    throw std::runtime_error(msg.str());
+  }
+}
+
+TCPSocket TCPSocket::accept(const char* tag) {
+  int peer = ::accept(sock_, nullptr, nullptr);
+  if (peer < 0) {
+    std::ostringstream msg;
+    msg << tag << " Accept failed (error: " << errno << ")";
+    throw std::runtime_error(msg.str());
+  }
+
+  return TCPSocket(peer);
+}
+
+void TCPSocket::send(const char* tag, const void* data, size_t len) {
+  while (len > 0) {
+    auto n = ::send(sock_, data, len, 0);
+    if (n <= 0) {
+      std::ostringstream msg;
+      msg << tag << " Send failed with errno=" << errno;
+      throw std::runtime_error(msg.str());
+    }
+    len -= n;
+    data = static_cast<const char*>(data) + n;
+  }
+}
+
+void TCPSocket::recv(const char* tag, void* data, size_t len) {
+  while (len > 0) {
+    auto n = ::recv(sock_, data, len, 0);
+    if (n <= 0) {
+      std::ostringstream msg;
+      msg << tag << " Recv failed with errno=" << errno;
+      throw std::runtime_error(msg.str());
+    }
+    len -= n;
+    data = static_cast<char*>(data) + n;
+  }
+}
+
+TCPSocket TCPSocket::connect(
+    const char* tag,
+    const address_t& addr,
+    int num_retries,
+    int wait,
+    std::function<void(int, int)> cb) {
+  int sock, success;
+
+  // Attempt to connect `num_retries` times with exponential backoff.
+  for (int attempt = 0; attempt < num_retries; attempt++) {
+    // Create the socket
+    sock = socket(AF_INET, SOCK_STREAM, 0);
+    if (sock < 0) {
+      std::ostringstream msg;
+      msg << tag << " Couldn't create socket to connect (error: " << errno
+          << ")";
+      throw std::runtime_error(msg.str());
+    }
+
+    success = ::connect(sock, addr.get(), addr.len);
+    if (success == 0) {
+      break;
+    }
+
+    cb(attempt, wait);
+    if (wait > 0) {
+      std::this_thread::sleep_for(std::chrono::milliseconds(wait));
+    }
+
+    wait <<= 1;
+  }
+
+  if (success < 0) {
+    std::ostringstream msg;
+    msg << tag << " Couldn't connect (error: " << errno << ")";
+    throw std::runtime_error(msg.str());
+  }
+
+  return TCPSocket(sock);
+}
+
+} // namespace mlx::core::distributed::detail

mlx/distributed/utils.h

@@ -0,0 +1,67 @@
+// Copyright © 2025 Apple Inc.
+
+#pragma once
+
+#include <sys/socket.h>
+#include <functional>
+#include <string>
+
+namespace mlx::core::distributed::detail {
+
+struct address_t {
+  sockaddr_storage addr;
+  socklen_t len;
+
+  const sockaddr* get() const {
+    return (struct sockaddr*)&addr;
+  }
+};
+
+/**
+ * Parse a sockaddr from an ip and port provided as strings.
+ */
+address_t parse_address(const std::string& ip, const std::string& port);
+
+/**
+ * Parse a sockaddr provided as an <ip>:<port> string.
+ */
+address_t parse_address(const std::string& ip_port);
+
+/**
+ * Small wrapper over a TCP socket to simplify initiating connections.
+ */
+class TCPSocket {
+ public:
+  TCPSocket(const char* tag);
+  TCPSocket(const TCPSocket&) = delete;
+  TCPSocket& operator=(const TCPSocket&) = delete;
+  TCPSocket(TCPSocket&& s);
+  TCPSocket& operator=(TCPSocket&&);
+  ~TCPSocket();
+
+  void listen(const char* tag, const address_t& addr);
+  TCPSocket accept(const char* tag);
+
+  void send(const char* tag, const void* data, size_t len);
+  void recv(const char* tag, void* data, size_t len);
+
+  int detach();
+
+  operator int() const {
+    return sock_;
+  }
+
+  static TCPSocket connect(
+      const char* tag,
+      const address_t& addr,
+      int num_retries = 1,
+      int wait = 0,
+      std::function<void(int, int)> cb = nullptr);
+
+ private:
+  TCPSocket(int sock);
+
+  int sock_;
+};
+
+} // namespace mlx::core::distributed::detail

python/mlx/_distributed_utils/common.py

@@ -0,0 +1,85 @@
+# Copyright © 2025 Apple Inc.
+
+import ipaddress
+import json
+import sys
+from dataclasses import dataclass
+from pathlib import Path
+from typing import Optional
+
+
+@dataclass
+class Host:
+    rank: int
+    ssh_hostname: str
+    ips: list[str]
+    rdma: list[Optional[str]]
+
+
+def positive_number(x):
+    x = int(x)
+    if x <= 0:
+        raise ValueError("Number should be positive")
+    return x
+
+
+def log(verbose, *args, **kwargs):
+    if not verbose:
+        return
+    print("\033[32m[INFO]", *args, "\033[0m", **kwargs)
+
+
+def log_warning(*args, **kwargs):
+    kwargs["file"] = sys.stderr
+    print("\033[33m[WARN]", *args, "\033[0m", **kwargs)
+
+
+def log_error(*args, **kwargs):
+    kwargs["file"] = sys.stderr
+    print("\033[31m[ERROR]", *args, "\033[0m", **kwargs)
+
+
+def parse_hostlist(parser, hostlist, repeats):
+    hosts = []
+    for i, h in enumerate(hostlist.split(",")):
+        if h == "":
+            raise ValueError("Hostname cannot be empty")
+        try:
+            ipaddress.ip_address(h)
+            ips = [h]
+        except ValueError:
+            ips = []
+        for i in range(repeats):
+            hosts.append(Host(i, h, ips))
+    return hosts
+
+
+def parse_hostfile(parser, hostfile):
+    """Parse the json hostfile that contains both the hostnames to ssh into and
+    the ips to communicate over when using the ring backend.
+
+    Example:
+
+        [
+            {"ssh": "hostname1", "ips": ["123.123.123.1"], "rdma": [null, "rdma_en2", "rdma_en3"]},
+            {"ssh": "hostname2", "ips": ["123.123.123.2"], "rdma": ["rdma_en2", null, "rdma_en3"]},
+            ...
+            {"ssh": "hostnameN", "ips": ["123.123.123.N"], "rdma": ["rdma_en2", "rdma_en3", null]},
+        ]
+
+    Args:
+        hostfile (str): The path to the json file containing the host
+            information
+    """
+    hostfile = Path(hostfile)
+    if not hostfile.exists():
+        parser.error(f"Hostfile {str(hostfile)} doesn't exist")
+
+    try:
+        hosts = []
+        with open(hostfile) as f:
+            for i, h in enumerate(json.load(f)):
+                hosts.append(Host(i, h["ssh"], h.get("ips", []), h.get("rdma", [])))
+        return hosts
+    except Exception as e:
+        parser.error(f"Failed to parse hostfile {str(hostfile)} ({str(e)})")

python/mlx/_distributed_utils/distributed_run.py

@@ -832,7 +832,7 @@ def main():
     parser.add_argument("--hostfile", help="The file containing the hosts")
     parser.add_argument(
         "--backend",
-        choices=["ring", "mpi", "nccl"],
+        choices=["ring", "mpi", "nccl", "jaccl"],
         default="nccl" if mx.cuda.is_available() else "ring",
         help="Which distributed backend to launch",
     )
@@ -903,6 +903,8 @@ def main():
         launch_mpi(parser, hosts, args, rest)
     if args.backend == "nccl":
         launch_nccl(parser, hosts, args, rest)
+    if args.backend == "jaccl":
+        launch_jaccl(parser, hosts, args, rest)
 
 
 if __name__ == "__main__":

python/mlx/_distributed_utils/launch.py

@@ -0,0 +1,540 @@
+# Copyright © 2025 Apple Inc.
+
+import argparse
+import base64
+import json
+import os
+import shlex
+import shutil
+import sys
+import tempfile
+import threading
+from collections import Counter
+from itertools import chain
+from pathlib import Path
+from queue import Empty as QueueEmpty
+from queue import Queue
+from select import select
+from subprocess import PIPE, Popen, run
+
+import mlx.core as mx
+
+from .common import log, log_warning, parse_hostfile, parse_hostlist, positive_number
+
+
+class CommandProcess:
+    @property
+    def process(self):
+        """Return the Popen object that refers to the current command."""
+        raise NotImplementedError()
+
+    @property
+    def exit_status(self):
+        """Return a tuple (returncode, killed) for the command. It should be
+        (None, None) while the command is running normally."""
+        raise NotImplementedError()
+
+    def preprocess_output(self, data: str, is_stdout=False):
+        """Preprocess the output of the command so that extra data can be
+        capture or the format changed on the fly."""
+        raise NotImplementedError()
+
+    def terminate(self):
+        """Terminate or return the exit code."""
+        raise NotImplementedError()
+
+
+class RemoteProcess(CommandProcess):
+    def __init__(self, rank, host, cwd, files, env, command):
+        is_local = host == "127.0.0.1"
+        script = RemoteProcess.make_monitor_script(rank, cwd, files, env, command)
+        script_b64 = base64.b64encode(script.encode()).decode()
+        cmd = f'{sys.executable} -c "import base64; exec(base64.b64decode(\\"{script_b64}\\"));"'
+        if not is_local:
+            cmd = f"ssh {host} '{cmd}'"
+
+        self._host = host
+        self._pidfile = None
+        self._is_local = is_local
+        self._process = Popen(
+            cmd,
+            shell=True,
+            stdin=PIPE,
+            stdout=PIPE,
+            stderr=PIPE,
+        )
+
+        self._killed = False
+
+    @property
+    def process(self):
+        return self._process
+
+    @property
+    def exit_status(self):
+        return self._process.poll(), self._killed
+
+    def preprocess_output(self, data, is_stdout=False):
+        if self._pidfile is None:
+            pidfile, *rest = data.split("\n", maxsplit=1)
+            self._pidfile = pidfile
+            return rest[0] if rest else ""
+
+        return data
+
+    def terminate(self):
+        if self._killed:
+            return
+
+        self._process.terminate()
+        self._process.wait()
+
+        # Kill the remote program if possible
+        cmd = ""
+        cmd += f"pid=$(cat {self._pidfile}); "
+        cmd += "if ps -p $pid >/dev/null; then "
+        cmd += "    kill $pid; "
+        cmd += "    echo 1; "
+        cmd += "else "
+        cmd += "    echo 0; "
+        cmd += "fi; "
+        cmd += f"rm {self._pidfile}"
+        if not self._is_local:
+            cmd = f"ssh {self._host} '{cmd}'"
+        c = run(cmd, check=True, shell=True, capture_output=True, text=True)
+
+        self._killed = c.stdout.strip() == "1"
+
+    @staticmethod
+    def make_monitor_script(rank, cwd, files, env, command):
+        # Imports that are used throughout
+        script = ""
+        script += "import os\n"
+        script += "import sys\n"
+        script += "import tempfile\n"
+        script += "from pathlib import Path\n"
+
+        # Write the PID to a file so we can kill the process if needed
+        script += "_, pidfile = tempfile.mkstemp() \n"
+        script += "open(pidfile, 'w').write(str(os.getpid()))\n"
+        script += "print(pidfile, flush=True)\n"
+
+        # Change the working directory if one was requested. Otherwise attempt to
+        # change to the current one but don't fail if it wasn't possible.
+        d = cwd or os.getcwd()
+        script += f"if Path({repr(d)}).exists():\n"
+        script += f"    os.chdir({repr(d)})\n"
+        if cwd is not None:
+            script += "else:\n"
+            script += f"    print('Failed to change directory to', {repr(d)}, file=sys.stderr)\n"
+            script += f"    sys.exit(1)\n"
+
+        # Add the environment variables that were requested
+        script += "env = dict(os.environ)\n"
+        for e in env:
+            key, *value = e.split("=", maxsplit=1)
+            value = shlex.quote(value[0]) if len(value) > 0 else ""
+            if not all(c.isalnum() or c == "_" for c in key):
+                log_warning(
+                    f"'{e}' is an invalid environment variable so it is ignored"
+                )
+                continue
+            script += f"env[{repr(key)}] = {repr(value)}\n"
+
+        # Make the temporary files
+        for env_name, content in files.items():
+            script += "_, fname = tempfile.mkstemp()\n"
+            script += "with open(fname, 'w') as f:\n"
+            script += f"    f.write({repr(content)})\n"
+            script += f"env[{repr(env_name)}] = fname\n"
+
+        # Finally add the rank
+        script += f"env['MLX_RANK'] = '{rank}'\n"
+        script += "\n"
+
+        # Replace the process with the script
+        script += f"command = [{','.join(map(repr, command))}]\n"
+        script += "os.execve(command[0], command, env)\n"
+
+        return script
+
+
+def _launch_with_io(command_class, arguments, verbose):
+    stop = False
+    exit_codes = [(None, None)] * len(arguments)
+
+    def _thread_fn(rank, *args, **kwargs):
+        stdin_queue = kwargs.pop("stdin_queue")
+        stdout_queue = kwargs.pop("stdout_queue")
+        stderr_queue = kwargs.pop("stderr_queue")
+
+        command = command_class(rank, *args, **kwargs)
+        p = command.process
+        os.set_blocking(p.stdout.fileno(), False)
+        os.set_blocking(p.stderr.fileno(), False)
+        os.set_blocking(p.stdin.fileno(), False)
+
+        to_read = [p.stdout.fileno(), p.stderr.fileno()]
+        to_write = [p.stdin.fileno()]
+
+        stdin_buffer = b""
+        while p.poll() is None:
+            try:
+                stdin_buffer += stdin_queue.get_nowait()
+            except QueueEmpty:
+                pass
+            rlist, wlist, _ = select(to_read, to_write, [], 1.0)
+            for fd in rlist:
+                is_stdout = fd == p.stdout.fileno()
+                msg = os.read(fd, 8192).decode(errors="ignore")
+                msg = command.preprocess_output(msg, is_stdout)
+                if is_stdout:
+                    stdout_queue.put(msg.encode())
+                else:
+                    stderr_queue.put(msg.encode())
+            for fd in wlist:
+                if len(stdin_buffer) > 0:
+                    n = os.write(fd, stdin_buffer)
+                    stdin_buffer = stdin_buffer[n:]
+            if stop:
+                command.terminate()
+                break
+        exit_codes[rank] = command.exit_status
+
+        if exit_codes[rank][1]:
+            log_warning(f"Node with rank {rank} was killed")
+        elif exit_codes[rank][0] != 0:
+            log_warning(f"Node with rank {rank} exited with code {exit_codes[rank][0]}")
+        else:
+            log(verbose, f"Node with rank {rank} completed")
+
+    stdin_queues = []
+    stdout_queues = []
+    stderr_queues = []
+    threads = []
+    for i, (args, kwargs) in enumerate(arguments):
+        stdin_queues.append(Queue())
+        stdout_queues.append(Queue())
+        stderr_queues.append(Queue())
+        t = threading.Thread(
+            target=_thread_fn,
+            args=args,
+            kwargs=kwargs
+            | {
+                "stdin_queue": stdin_queues[-1],
+                "stdout_queue": stdout_queues[-1],
+                "stderr_queue": stderr_queues[-1],
+            },
+        )
+        t.start()
+        threads.append(t)
+
+    os.set_blocking(sys.stdin.fileno(), False)
+    os.set_blocking(sys.stdout.fileno(), True)
+    os.set_blocking(sys.stderr.fileno(), True)
+    while not stop or any(not q.empty() for q in chain(stdout_queues, stderr_queues)):
+        # Broadcast user input to the jobs
+        rlist, _, _ = select([sys.stdin.fileno()], [], [], 0.1)
+        for fd in rlist:
+            stdin_buffer = os.read(fd, 8192)
+            for q in stdin_queues:
+                q.put(stdin_buffer)
+
+        # Gather job output
+        for q in stdout_queues:
+            try:
+                while not q.empty():
+                    sys.stdout.buffer.write(q.get_nowait())
+            except QueueEmpty:
+                pass
+        for q in stderr_queues:
+            try:
+                while not q.empty():
+                    sys.stderr.buffer.write(q.get_nowait())
+            except QueueEmpty:
+                pass
+        sys.stdout.buffer.flush()
+        sys.stderr.buffer.flush()
+
+        # Check if all are running and terminate otherwise
+        if any(t.is_alive() for t in threads):
+            for i, t in enumerate(threads):
+                if not t.is_alive():
+                    if exit_codes[i][0] != 0:
+                        stop = True
+                        break
+        else:
+            break
+
+    # Wait for the jobs to finish
+    for t in threads:
+        t.join()
+
+    # Process any remaining outputs
+    for q in stdout_queues:
+        while not q.empty():
+            sys.stdout.buffer.write(q.get())
+    for q in stderr_queues:
+        while not q.empty():
+            sys.stderr.buffer.write(q.get())
+    sys.stdout.buffer.flush()
+    sys.stderr.buffer.flush()
+
+
+def launch_ring(parser, hosts, args, command):
+    if any(len(h.ips) == 0 for h in hosts):
+        parser.error(
+            "The ring backend requires IPs to be provided instead of hostnames"
+        )
+
+    port = args.starting_port
+    ring_hosts = []
+    for h in hosts:
+        node = []
+        for ip in h.ips:
+            for i in range(args.connections_per_ip):
+                node.append(f"{ip}:{port}")
+                port += 1
+        ring_hosts.append(node)
+    hostfile = json.dumps(ring_hosts) if len(ring_hosts) > 1 else ""
+
+    files = {"MLX_HOSTFILE": hostfile}
+    env = args.env
+    if args.verbose:
+        env.append("MLX_RING_VERBOSE=1")
+    cwd = args.cwd
+
+    log(args.verbose, "Running", shlex.join(command))
+
+    _launch_with_io(
+        RemoteProcess,
+        [
+            ((rank, h.ssh_hostname, cwd, files, env, command), {})
+            for rank, h in enumerate(hosts)
+        ],
+        args.verbose,
+    )
+
+
+def launch_nccl(parser, hosts, args, command):
+    if not hosts[0].ips:
+        raise ValueError("Rank 0 should have an IP reachable from all other ranks")
+
+    master_host = hosts[0].ips[0]
+    master_port = args.nccl_port
+    world_size = len(hosts)
+
+    env = args.env
+    cwd = args.cwd
+    if args.verbose:
+        env.append("NCCL_DEBUG=INFO")
+    env.append(f"NCCL_HOST_IP={master_host}")
+    env.append(f"NCCL_PORT={master_port}")
+    env.append(f"MLX_WORLD_SIZE={world_size}")
+
+    log(args.verbose, "Running", shlex.join(command))
+
+    _launch_with_io(
+        RemoteProcess,
+        [
+            (
+                (
+                    rank,
+                    h.ssh_hostname,
+                    cwd,
+                    {},
+                    env + [f"CUDA_VISIBLE_DEVICES={rank % args.repeat_hosts}"],
+                    command,
+                ),
+                {},
+            )
+            for rank, h in enumerate(hosts)
+        ],
+        args.verbose,
+    )
+
+
+def launch_jaccl(parser, hosts, args, command):
+    if not hosts[0].ips:
+        raise ValueError("Rank 0 should have an IP reachable from all other ranks")
+
+    have_rdmas = all(len(h.rdma) == len(hosts) for h in hosts)
+    have_nulls = all(h.rdma[i] is None for i, h in enumerate(hosts))
+    if not have_rdmas or not have_nulls:
+        raise ValueError("Malformed hostfile for jaccl backend")
+
+    coordinator = hosts[0].ips[0]
+    env = args.env
+    cwd = args.cwd
+    env.append(f"MLX_JACCL_COORDINATOR={coordinator}:{args.starting_port}")
+    files = {"MLX_IBV_DEVICES": json.dumps([h.rdma for h in hosts])}
+
+    log(args.verbose, "Running", shlex.join(command))
+
+    _launch_with_io(
+        RemoteProcess,
+        [
+            ((rank, h.ssh_hostname, cwd, files, env, command), {})
+            for rank, h in enumerate(hosts)
+        ],
+        args.verbose,
+    )
+
+
+def get_mpi_libname():
+    try:
+        ompi_info = run(["which", "ompi_info"], check=True, capture_output=True)
+        ompi_info = ompi_info.stdout.strip().decode()
+
+        if platform.system() == "Darwin":
+            otool_output = run(
+                ["otool", "-L", ompi_info], check=True, capture_output=True
+            )
+        else:
+            otool_output = run(["ldd", ompi_info], check=True, capture_output=True)
+        otool_output = otool_output.stdout.decode()
+
+        # StopIteration if not found
+        libmpi_line = next(
+            filter(lambda line: "libmpi" in line, otool_output.splitlines())
+        )
+        return libmpi_line.strip().split()[0].removeprefix("@rpath/")
+    except:
+        return None
+
+
+def launch_mpi(parser, hosts, args, command):
+    mpirun = run(["which", "mpirun"], check=True, capture_output=True)
+    mpirun = mpirun.stdout.strip().decode()
+
+    # Compatibility with homebrew and pip installs
+    mpi_libname = get_mpi_libname()
+    if mpi_libname is not None:
+        dyld = Path(mpirun).parent.parent / "lib"
+        args.env = [
+            f"DYLD_LIBRARY_PATH={str(dyld)}",
+            f"MLX_MPI_LIBNAME={mpi_libname}",
+        ] + args.env
+
+    log(args.verbose, f"Using '{mpirun}'")
+    with tempfile.NamedTemporaryFile(mode="w") as f:
+        hosts = Counter((h.ssh_hostname for h in hosts))
+        for h, n in hosts.items():
+            print(f"{h} slots={n}", file=f)
+        f.flush()
+
+        cmd = [
+            mpirun,
+            "--output",
+            ":raw",  # do not line buffer output
+            "--hostfile",
+            f.name,
+            *(["-cwd", args.cwd] if args.cwd else []),
+            *sum((["-x", e] for e in args.env), []),
+            *sum([shlex.split(arg) for arg in args.mpi_arg], []),
+            "--",
+            *command,
+        ]
+        log(args.verbose, "Running", " ".join(cmd))
+        try:
+            run(cmd)
+        except KeyboardInterrupt:
+            pass
+
+
+def main():
+    parser = argparse.ArgumentParser(description="Launch an MLX distributed program")
+    parser.add_argument(
+        "--print-python",
+        action="store_true",
+        help="Print the path to the current python executable and exit",
+    )
+    parser.add_argument(
+        "--verbose", action="store_true", help="Print debug messages in stdout"
+    )
+    parser.add_argument(
+        "--hosts", default="127.0.0.1", help="A comma separated list of hosts"
+    )
+    parser.add_argument(
+        "--repeat-hosts",
+        "-n",
+        type=positive_number,
+        default=1,
+        help="Repeat each host a given number of times",
+    )
+    parser.add_argument("--hostfile", help="The file containing the hosts")
+    parser.add_argument(
+        "--backend",
+        choices=["ring", "mpi", "nccl", "jaccl"],
+        default="nccl" if mx.cuda.is_available() else "ring",
+        help="Which distributed backend to launch",
+    )
+    parser.add_argument(
+        "--env",
+        action="append",
+        default=[],
+        help="Set environment variables for the jobs",
+    )
+    parser.add_argument(
+        "--mpi-arg",
+        action="append",
+        default=[],
+        help="Arguments to pass directly to mpirun",
+    )
+    parser.add_argument(
+        "--connections-per-ip",
+        default=1,
+        type=int,
+        help="How many connections per ip to use for the ring backend",
+    )
+    parser.add_argument(
+        "--starting-port",
+        "-p",
+        type=int,
+        default=32323,
+        help="For the ring backend listen on this port increasing by 1 per rank and IP",
+    )
+    parser.add_argument(
+        "--cwd", help="Set the working directory on each node to the provided one"
+    )
+    parser.add_argument(
+        "--nccl-port",
+        type=int,
+        default=12345,
+        help="The port to use for the NCCL communication (only for nccl backend)",
+    )
+
+    args, rest = parser.parse_known_args()
+
+    if args.print_python:
+        print(sys.executable)
+        return
+
+    if len(rest) == 0:
+        parser.error("No script is provided")
+    if rest[0] == "--":
+        rest.pop(0)
+
+    # Try to extract a list of hosts and corresponding ips
+    if args.hostfile is not None:
+        hosts = parse_hostfile(parser, args.hostfile)
+    else:
+        hosts = parse_hostlist(parser, args.hosts, args.repeat_hosts)
+
+    # Check if the script is a file and convert it to a full path
+    if (script := Path(rest[0])).exists() and script.is_file():
+        rest[0:1] = [sys.executable, str(script.resolve())]
+    elif (command := shutil.which(rest[0])) is not None:
+        rest[0] = command
+    else:
+        raise ValueError(f"Invalid script or command {rest[0]}")
+
+    # Launch
+    if args.backend == "ring":
+        launch_ring(parser, hosts, args, rest)
+    if args.backend == "mpi":
+        launch_mpi(parser, hosts, args, rest)
+    if args.backend == "nccl":
+        launch_nccl(parser, hosts, args, rest)
+    if args.backend == "jaccl":
+        launch_jaccl(parser, hosts, args, rest)

python/src/distributed.cpp

@@ -52,9 +52,25 @@ void init_distributed(nb::module_& parent_module) {
 
   m.def(
       "is_available",
-      &mx::distributed::is_available,
+      [](const std::string& backend) {
+        return mx::distributed::is_available(backend);
+      },
+      "backend"_a = "any",
+      nb::sig("def is_available(backend: str = 'any') -> bool"),
       R"pbdoc(
       Check if a communication backend is available.
+
+      Note, this function returns whether MLX has the capability of
+      instantiating that distributed backend not whether it is possible to
+      create a communication group. For that purpose one should use
+      ``init(strict=True)``.
+
+      Args:
+        backend (str, optional): The name of the backend to check for availability.
+          It takes the same values as ``init()``. Default: ``any``.
+
+      Returns:
+        bool: Whether the distributed backend is available.
       )pbdoc");
 
   m.def(
@@ -79,10 +95,10 @@ void init_distributed(nb::module_& parent_module) {
             in case ``mx.distributed.is_available()`` returns False otherwise
             it throws a runtime error. Default: ``False``
           backend (str, optional): Which distributed backend to initialize.
-            Possible values ``mpi``, ``ring``, ``nccl``, ``any``. If set to ``any`` all
-            available backends are tried and the first one that succeeds
-            becomes the global group which will be returned in subsequent
-            calls. Default: ``any``
+            Possible values ``mpi``, ``ring``, ``nccl``, ``jaccl``, ``any``. If
+            set to ``any`` all available backends are tried and the first one
+            that succeeds becomes the global group which will be returned in
+            subsequent calls. Default: ``any``
 
         Returns:
           Group: The group representing all the launched processes.

setup.py

@@ -257,8 +257,8 @@ if __name__ == "__main__":
     }
     entry_points = {
         "console_scripts": [
-            "mlx.launch = mlx.distributed_run:main",
-            "mlx.distributed_config = mlx.distributed_run:distributed_config",
+            "mlx.launch = mlx._distributed_utils.launch:main",
+            # "mlx.distributed_config = mlx.distributed_run:distributed_config",
         ]
     }
     install_requires = []