text: // Copyright 2020 Google LLC
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  //     http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  
  #ifndef SANDBOXED_API_SANDBOX2_FORK_CLIENT_H_
  #define SANDBOXED_API_SANDBOX2_FORK_CLIENT_H_
  
  #include <sys/types.h>
  
  #include "absl/base/attributes.h"
  #include "absl/synchronization/mutex.h"
  
  namespace sandbox2 {
  
  // Envvar indicating that this process should not start the fork-server.
  ABSL_CONST_INIT extern const char kForkServerDisableEnv[];
  
  class Comms;
  class ForkRequest;
  
  class ForkClient {
   public:
    ForkClient(const ForkClient&) = delete;
    ForkClient& operator=(const ForkClient&) = delete;
  
    explicit ForkClient(Comms* comms) : comms_(comms) {}
  
    // Sends the fork request over the supplied Comms channel.
    pid_t SendRequest(const ForkRequest& request, int exec_fd, int comms_fd,
                      int user_ns_fd = -1, pid_t* init_pid = nullptr);
  
   private:
    // Comms channel connecting with the ForkServer. Not owned by the object.
    Comms* comms_;
    // Mutex locking transactions (requests) over the Comms channel.
    absl::Mutex comms_mutex_;
  };
  }  // namespace sandbox2
  
  #endif  // SANDBOXED_API_SANDBOX2_FORK_CLIENT_H_
  