Have each SandboxedProcessLauncherDelegate maintain a zygote.

content/browser/zygote_host/zygote_communication_linux.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_COMMON_ZYGOTE_COMMUNICATION_H_
+#define CONTENT_COMMON_ZYGOTE_COMMUNICATION_H_
+
+#include <set>
+#include <vector>
+
+#include "base/process/kill.h"
+#include "base/synchronization/lock.h"
+#include "content/common/content_export.h"
+#include "content/public/browser/file_descriptor_info.h"
+
+namespace content {
+
+class CONTENT_EXPORT ZygoteCommunication {
+ public:
+  ZygoteCommunication();
+  ~ZygoteCommunication();
+
+  void Init();
+
+  // Tries to start a process of type indicated by process_type.
+  // Returns its pid on success, otherwise
+  // base::kNullProcessHandle;
+  pid_t ForkRequest(const std::vector<std::string>& command_line,
+                    scoped_ptr<FileDescriptorInfo> mapping,
+                    const std::string& process_type);
+
+  void EnsureProcessTerminated(pid_t process);
+
+  // Should be called every time a Zygote child died.
+  void ZygoteChildDied(pid_t process);
+
+  // Get the termination status (and, optionally, the exit code) of
+  // the process. |exit_code| is set to the exit code of the child
+  // process. (|exit_code| may be NULL.)
+  // Unfortunately the Zygote can not accurately figure out if a process
+  // is already dead without waiting synchronously for it.
+  // |known_dead| should be set to true when we already know that the process
+  // is dead. When |known_dead| is false, processes could be seen as
+  // still running, even when they're not. When |known_dead| is true, the
+  // process will be SIGKILL-ed first (which should have no effect if it was
+  // really dead). This is to prevent a waiting waitpid() from blocking in
+  // a single-threaded Zygote. See crbug.com/157458.
+  base::TerminationStatus GetTerminationStatus(base::ProcessHandle handle,
+                                               bool known_dead,
+                                               int* exit_code);
+
+  // Returns the sandbox status of this zygote.
+  int GetSandboxStatus();
+
+ private:
+  // Whether we should use the namespace sandbox instead of the setuid sandbox.
+  bool ShouldUseNamespaceSandbox();
+
+  // Should be called every time a Zygote child is born.
+  void ZygoteChildBorn(pid_t process);
+
+  // Read the reply from the zygote.
+  ssize_t ReadReply(void* buf, size_t buf_len);
+
+  // Sends |data| to the zygote via |control_fd_|.  If |fds| is non-NULL, the
+  // included file descriptors will also be passed.  The caller is responsible
+  // for acquiring |control_lock_|.
+  bool SendMessage(const base::Pickle& data, const std::vector<int>* fds);
+
+  // Get the sandbox status from the zygote.
+  ssize_t ReadSandboxStatus();
+
+  // Set to true when this is initialiazed successfuly.

[mdempsky, 2016/01/05 22:41:57]

Typo: "initialized" and "successfully"

[Greg K, 2016/01/06 18:20:41]

Done.

+  bool init_;

[mdempsky, 2016/01/05 22:41:57]

I'd put this next to the other bools below so we have less wasted space from
alignment padding of the member variables.

[Greg K, 2016/01/06 18:20:41]

Done.

+  int control_fd_;  // the socket to the zygote.
+  // A lock protecting all communication with the zygote. This lock must be
+  // acquired before sending a command and released after the result has been
+  // received.
+  base::Lock control_lock_;
+  // The pid of the zygote.
+  pid_t pid_;
+  // The listen of running zygote children.

[mdempsky, 2016/01/05 22:41:57]

Typo: "list"

[Greg K, 2016/01/06 18:20:41]

Done.

+  std::set<pid_t> list_of_running_zygote_children_;
+  // The lock to guard the list of running zygote children.
+  base::Lock child_tracking_lock_;
+  bool have_read_sandbox_status_word_;
+  bool use_suid_sandbox_for_adj_oom_score_;
+  int sandbox_status_;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_COMMON_ZYGOTE_COMMUNICATION_H_