Prototype implementation of zygotes

base/zygote_manager.h

+// Copyright (c) 2009 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 BASE_ZYGOTE_MANAGER_H_
+#define BASE_ZYGOTE_MANAGER_H_
+
+#include "build/build_config.h"
+
+#if defined(OS_LINUX)
+
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <map>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "base/pickle.h"
+#include "base/time.h"
+#include "base/process_util.h"  // for file_handle_mapping_vector
+
+namespace base {
+
+class ZygoteManager {
+ public:
+  // The normal way to get a ZygoteManager is via this singleton factory.
+  static ZygoteManager* Get();
+
+  ZygoteManager() : server_fd_(-1), client_fd_(-1), canary_fd_(-1),
+      lockfd_(-1) {
+  }
+
+  ~ZygoteManager();
+
+  // Measure round trip time.  Return true on success.
+  // Only used during testing.
+  bool Ping(base::TimeDelta* delta);
+
+  // Start the zygote manager.
+  // Called only once, but returns many times.
+  // Returns once in original process and once in each spawned child.
+  // In original process, returns NULL.
+  // In child processes, returns the argv to use for the child.
+  // In Chromium, called from ChromeMain().
+  std::vector<std::string>* Start();
+
+  // Like longjmp() and base::LaunchApp().
+  // Ask the fork server to spawn a new process with
+  // the given commandline and the given file descriptors.
+  // Returns process id of copy, or -1 on failure.
+  // In Chromium, called from base::ForkApp(), which is
+  // called from BrowserRenderProcessHost::Init().
+  pid_t LongFork(const std::vector<std::string>& argv,
+    const file_handle_mapping_vector& fds_to_remap);
+
+  // Tell ZygoteManager that we expect the given process to
+  // exit on its own soon.  If it doesn't die within a few
+  // seconds, kill it.  Does not block (unless pipe to server full).
+  // In Chromium, called from ProcessWatcher::EnsureProcessTerminated().
+  void EnsureProcessTerminated(pid_t childpid);
+
+  // Open a file, or retrieve a previously cached file descriptor
+  // for this file.  The files are opened for readonly access.
+  // Caution: do not seek file descriptors returned
+  // by this API, as all children share the same file objects, so
+  // a seek on one is a seek on all.
+  // Works even if the file is unlinked after the first call
+  // (e.g. when an app is updated by the linux system autoupdater).
+  // Returns file descriptor, or -1 for error.
+  // In Chromium, called from MemoryMappedFile::MapFileToMemory().
+  // Only allows openeing files named .pak in reasonable looking locations.
+  int OpenFile(const std::string& filename);
+
+ private:
+  int UnpickleHeader(const Pickle& reply, void** iter);
+
+  // Returns false on EOF
+  // Sets *newargv to a new commandline if the remote side requested a fork.
+  bool ReadAndHandleMessage(std::vector<std::string>** newargv);
+
+  void PingHandler(const Pickle& request, void* iter, Pickle* reply,
+                   std::vector<std::string>** newargv);
+
+  bool LongForkHandler(const Pickle& request, void* iter, Pickle* reply,
+                   std::vector<std::string>** newargv,
+                   const int wire_fds[], int num_wire_fds);
+
+  void EnsureProcessTerminatedHandler(const Pickle& request, void* iter);
+
+  bool OpenFileHandler(const Pickle& request, void* iter, Pickle* reply,
+      ::msghdr* msg);
+
+  // The fd used by the server to receive requests
+  int server_fd_;
+
+  // The fd used by the clients to send requests
+  int client_fd_;
+
+  // fd used only to notify server of destruction.
+  int canary_fd_;
+
+  // Temporary file used only for locking.
+  // Each client must do its own open for locking to work;
+  // inherited file descriptors can't lock each other out.
+  // FIXME: locking is lame.
+  std::string lockfile_;
+  int lockfd_;
+
+  enum message_kind_t { ZMPING, ZMPINGED,
+                ZMFORK, ZMFORKED,
+                ZMREAP,
+                ZMOPEN, ZMOPENED,
+                ZMBAD };
+
+  // See common/reserved_file_descriptors.h for who uses the reserved
+  // file descriptors.  kReservedFds is one plus the highest fd mentioned there.
+  // TODO(dkegel): move kReservedFds to reserved_file_descriptors.h
+  static const int kReservedFds = 5;
+
+  static const int kMAX_MSG_LEN = 2000;
+  static const int kMAX_CMSG_LEN = 100;
+
+  static const char kZMagic[];
+
+  char msg_buf_[kMAX_MSG_LEN];
+  char cmsg_buf_[kMAX_CMSG_LEN];
+
+  // Where we remember file descriptors for already-opened files.
+  // Both client and server maintain this table.
+  // Client should check the table before requesting the
+  // server to open a file, as it might have been already
+  // opened before this client was forked.
+  std::map<std::string, int> cached_fds_;
+};
+
+}  // namespace base
+
+#endif  // defined(OS_LINUX)
+
+#endif  // BASE_ZYGOTE_MANAGER_H_