/* -*- C++ -*- */
// $Id$

// ============================================================================
//
// = LIBRARY
//    ace
//
// = FILENAME
//    Process_Manager.h
//
// = AUTHOR
//    Douglas C. Schmidt <schmidt@cs.wustl.edu>
//
// ============================================================================

#ifndef ACE_PROCESS_MANAGER_H
#define ACE_PROCESS_MANAGER_H
#include "ace/pre.h"

#include "ace/Synch.h"
#include "ace/Reactor.h"
#include "ace/Event_Handler.h"

#if !defined (ACE_LACKS_PRAGMA_ONCE)
# pragma once
#endif /* ACE_LACKS_PRAGMA_ONCE */

#include "ace/Process.h"

class ACE_Export ACE_Process_Descriptor
{
  // = TITLE
  //    Information describing each process that's controlled by an
  //    <ACE_Process_Manager>.
private:
  friend class ACE_Process_Manager;

  ACE_Process_Descriptor (void);
  ~ACE_Process_Descriptor (void);
  // Default ctor/dtor.

  ACE_Process *process_;
  // Describes the process itself.

  ACE_Event_Handler *exit_notify_;
  // function to call when process exits

  void dump (void) const;
  // Dump the state of an object.
};

class ACE_Export ACE_Process_Manager : protected ACE_Event_Handler
{
  // = TITLE
  //    Manages a group of processes.
  //
  // = DESCRIPTION
  //    This class allows applications to control groups of processes,
  //    similar to how the <ACE_Thread_Manager> controls groups of
  //    threads.  Naturally, it doesn't work at all on platforms, such
  //    as VxWorks or pSoS, that don't support process.
  //
  //    There are two (main) ways of using <ACE_Process_Manager>,
  //    depending on how involved you wish to be with the termination
  //    of managed <ACE_Process>es.  If you just want <Process>es to
  //    go away when they're finished, simply register the
  //    <Process_Manager> with an <ACE_Reactor>:
  //
  //        ACE_Process_Manager mgr( 100, some_reactor )
  //         -or-
  //        ACE_Process_Manager mgr;
  //        ...
  //        mgr.open( 100, some_reactor );
  //
  //    Then, the <Process_Manager> will clean up after any
  //    <Process>es that it spawns.  (On Unix, this means executing a
  //    wait(2) to collect the exit status -- and avoid zombie
  //    processes; on Win32, it means closing the process and thread
  //    HANDLEs that are created when CreateProcess is called.)
  //
  //    If, on the other hand (and for some inexplicable reason) you
  //    want to explicitly invoke the terminated <Process> cleanup
  //    code, then *don't* register the <Process_Manager> with a
  //    Reactor, and be sure to call one of the
  //    <Process_Manager::wait> functions whenever there might be
  //    managed <Process>es that have exited.
  //
  //    Note that in either case, <Process_Manager> allows you to
  //    register "<Event_Handlers>" to be called when a specific
  //    <Process> exits, or when any <Process> without a specific
  //    <Event_Handler> exits.  When a <Process> exits, the
  //    appropriate <Event_Handler>'s <handle_input> is called; the
  //    <ACE_HANDLE> passed is either the Process' HANDLE (on Win32),
  //    or its pid cast to an <ACE_HANDLE> (on unix).
  //
  //    It is also possible to call the <Process_Manager::wait>
  //    functions even though the <Process_Manager> is registered with
  //    a <Reactor>.  I don't know what happens in this case, but it's
  //    probably not *too* bad.
  //
  //    Note also that the wait functions are "sloppy" on Unix,
  //    because there's no good way to wait for a subset of the
  //    children of a process.  The wait functions may end up
  //    collecting the exit status of a process that's not managed by
  //    the <Process_Manager> whose <wait> you invoked.  It's best to
  //    only use a single <Process_Manager>, and to create all
  //    subprocesses by calling that <Process_Manager>'s <spawn>
  //    method.  (I have some ideas for workarounds to improve this
  //    situation, but I consider it fairly low priority because I
  //    think the "single <Process_Manager>" pattern will be
  //    sufficient in most cases.)
  //
  //    Incidentally, when you register your <Process_Manager> with a
  //    <Reactor> its notification pipe is used to help "reap" the
  //    available exit statuses.  Therefore, you must not use a
  //    <Reactor> whose notify pipe has been disabled.  Here's the
  //    sequence of steps used to reap the exit statuses in this case:
  //
  //    * The <Process_Manager> registers a signal handler for
  //      SIGCHLD.
  //
  //    * The SIGCHLD handler, when invoked, uses the <Reactor>'s
  //      <notify> method to inform the <Reactor> to wake up.
  //
  //    * Next, the <Reactor> calls the <Process_Manager>'s
  //      <handle_input>, this happens synchronously, not in
  //      sighandler-space.
  //
  //    * The <handle_input> method collects all available exit
  //      statuses.
public:
  friend class ACE_Process_Control;

  enum
  {
    DEFAULT_SIZE = 100
  };

  // = Initialization and termination methods.
  ACE_Process_Manager (size_t size = ACE_Process_Manager::DEFAULT_SIZE,
                       ACE_Reactor *reactor = 0);
  // Initialize an <ACE_Process_Manager> with a table containing up to
  // <size> processes.  This table resizes itself automatically as
  // needed.  If a non-NULL <reactor> is provided, this
  // <ACE_Process_Manager> uses it to notify an application when a
  // process it controls exits.  By default, however, we don't use an
  // <ACE_Reactor>.

  int open (size_t size = DEFAULT_SIZE,
            ACE_Reactor *r = 0);
  // Initialize an <ACE_Process_Manager> with a table containing up to
  // <size> processes.  This table resizes itself automatically as
  // needed.  If a non-NULL <reactor> is provided, this
  // <ACE_Process_Manager> uses it to notify an application when a
  // process it controls exits.  By default, however, we don't use an
  // <ACE_Reactor>.

  int close (void);
  // Release all resources.  Do not wait for processes to exit.

  virtual ~ACE_Process_Manager (void);
  // Destructor releases all resources and does not wait for processes
  // to exit.

  // = Singleton accessors.
  static ACE_Process_Manager *instance (void);
  // Get pointer to a process-wide <ACE_Process_Manager>.

  static ACE_Process_Manager *instance (ACE_Process_Manager *);
  // Set pointer to a process-wide <ACE_Process_Manager> and return
  // existing pointer.

  static void close_singleton (void);
  // Delete the dynamically allocated singleton.

  // = Process creation methods.

  pid_t spawn (ACE_Process *proc,
               ACE_Process_Options &options);
  // Create a new process by passing <options> to <proc.spawn>.  On
  // success, returns the process id of the child that was created.
  // On failure, returns ACE_INVALID_PID.

  pid_t spawn (ACE_Process_Options &options);
  // Create a new process by passing <options> to
  // <ACE_Process::spawn>.  On success, returns the process id of the
  // child that was created.  On failure, returns ACE_INVALID_PID.

  int spawn_n (size_t n,
               ACE_Process_Options &options,
               pid_t *child_pids = 0);
  // Create <n> new processes by passing <options> to
  // <ACE_Process::spawn>, which is called <n> times.  If <child_pids>
  // is non-0 it is expected to be an array of <n> <pid_t>'s, which
  // are filled in with the process ids of each newly created process.
  // Returns 0 on success and -1 on failure.

  // = Process synchronization operations.

  int wait (const ACE_Time_Value &timeout = ACE_Time_Value::max_time);
  // Block until there are no more child processes running that were
  // <spawn>ed by this <ACE_Process_Manager>.  Unlike the <wait> call
  // below, this method does not require a signal handler or
  // <ACE_OS::sigwait> because it simply blocks synchronously waiting
  // for all the children managed by this <ACE_Process_Manager> to
  // exit.  Note that this does not return any status information
  // about the success or failure of exiting child processes, although
  // any registered exit_handlers are called.  Returns 0 on success
  // (and <remove>s the corresponding <ACE_Process_Descriptor> entries
  // from the <Process_Manager>; otherwise, returns -1 on failure.

  pid_t wait (pid_t pid,
              const ACE_Time_Value &timeout,
              ACE_exitcode *status = 0);
  // Wait up to <timeout> for a single process to terminate.  If
  // pid==0, waits for any of the managed <Process>es (but see the
  // note in DESCRIPTION above for caveats about this -- "sloppy
  // Process cleanup on unix") If pid != 0, waits for that <Process>
  // only.  Returns the pid of the Process whose exit was handled, 0
  // if a timeout occurred, or ACE_INVALID_PID on error.

  pid_t wait (pid_t pid,
              ACE_exitcode *status = 0);
  // Wait indefinitely for a single process to terminate.  If pid==0,
  // waits for any of the managed <Process>es (but see the note in
  // DESCRIPTION above for caveats about this -- "sloppy Process
  // cleanup on unix") If pid != 0, waits for that <Process> only.
  // Returns the pid of the process whose exit was handled, or
  // ACE_INVALID_PID on error.

  int reap (pid_t pid = -1,
            ACE_exitcode *stat_loc = 0,
            int options = WNOHANG);
  // Reap the result of a single process by calling <ACE_OS::waitpid>,
  // therefore, this method is not portable to Win32.  If the child is
  // successfully reaped, <remove> is called automatically.  This
  // method does the same thing that the <wait> method directly above
  // it does -- It's just here for backwards compatibility.

  // = Utility methods.
  int register_handler (ACE_Event_Handler *event_handler,
                        pid_t pid = ACE_INVALID_PID);
  // Register an Event_Handler to be called back when the specified
  // process exits.  If pid == ACE_INVALID_PID this handler is called
  // when any process with no specific handler exits.

  int remove (pid_t pid);
  // Remove process <pid> from the table.  This is called
  // automatically by the <reap> method after it successfully reaped a
  // <SIGCHLD> signal.  It's also possible to call this method
  // directly from a signal handler, but don't call both <reap> and
  // <remove>!

  int terminate (pid_t pid);
  // Abruptly terminate a single process with id <pid> using the
  // <ACE::terminate_process> method.  Note that this call is
  // potentially dangerous to use since the process being terminated
  // may not have a chance to cleanup before it shuts down.  Returns 0
  // on success and -1 on failure.

  int terminate (pid_t pid,
                 int sig);
  // On OSs that support signals, send the signal to the specified
  // process.  Returns 0 on success and -1 on failure.

  size_t managed (void) const;
  // Return the number of managed Processes.

  void dump (void) const;
  // Dump the state of an object.

  ACE_ALLOC_HOOK_DECLARE;
  // Declare the dynamic allocation hooks.

protected:
  // = These methods allow a <Process_Manager> to be an <Event_Handler>.

  // As an <Event_Handler>, the <Process_Manager> automagically
  // detects child Processes exiting and calls notify_proc_handler()
  // and remove().  This means that you don't have to (shouldn't!)
  // call the wait(...)  methods yourself.

  // On Unix, we can't detect individual process termination very
  // well; the best method is to catch SIGCHLD and then call the
  // polling wait() function to collect any available exit statuses.
  // However, we don't want to do this from within a signal handler
  // because of the restrictions associated.  Therefore (following the
  // lead in examples/mumble) we open a bogus handle (to ACE_DEV_NULL)
  // and register that handle with our Reactor.  Then, when our
  // SIGCHLD handler gets invoked, we tell the Reactor that the bogus
  // handle is readable.  That will cause the handle_input() function
  // to be called once we're out of the interrupt context, and
  // handle_input() collects exit statuses.

  // On Win32, we simply register ourself with the Reactor to deal
  // with the Process handle becoming signaled.  No muss, no fuss, no
  // signal handler, and no dummy handle.

#if !defined(ACE_WIN32)
  virtual int handle_input (ACE_HANDLE proc);
  // Collect one (or more, on unix) process exit status.
#endif // !defined(ACE_WIN32)

  virtual int handle_signal (int signum,
                             siginfo_t * = 0,
                             ucontext_t * = 0);
  // On Unix, this routine is called asynchronously when a SIGCHLD is
  // received.  We just tweak the reactor so that it'll call back our
  // <handle_input> function, which allows us to handle Process exits
  // synchronously.
  //
  // On Win32, this routine is called synchronously, and is passed the
  // HANDLE of the Process that exited, so we can do all our work here

private:
  int resize (size_t);
  // Resize the pool of Process_Descriptors.

  ssize_t find_proc (pid_t process_id);
  // Locate the index of the table slot occupied by <process_id>.
  // Returns -1 if <process_id> is not in the <process_table_>

#if defined (ACE_WIN32)
  ssize_t find_proc (ACE_HANDLE process_handle);
  // Locate the index of the table slot occupied by <process_handle>.
  // Returns ~0 if <process_handle> is not in the <process_table_>
#endif /* ACE_WIN32 */

  int insert_proc (ACE_Process *process);
  // Insert a process in the table (checks for duplicates).  Omitting
  // the process handle won't work on Win32...

  int append_proc (ACE_Process *process);
  // Append information about a process, i.e., its <process_id> in the
  // <process_table_>.  Each entry is added at the end, growing the
  // table if necessary.

  int remove_proc (size_t n);
  // Actually removes the process at index <n> from the table.  This method
  // must be called with locks held.

  int notify_proc_handler (size_t n,
                           ACE_exitcode status);
  // If there's a specific handler for the Process at index <n> in the
  // table, or there's a default handler, call it.

  ACE_Process_Descriptor *process_table_;
  // Vector that describes process state within the Process_Manager.

  size_t max_process_table_size_;
  // Maximum number of processes we can manage (should be dynamically
  // allocated).

  size_t current_count_;
  // Current number of processes we are managing.

  ACE_Event_Handler *default_exit_handler_;
  // This event handler is used to notify when a process we control
  // exits.

  static ACE_Process_Manager *instance_;
  // Singleton pointer.

  static int delete_instance_;
  // Controls whether the <Process_Manager> is deleted when we shut
  // down (we can only delete it safely if we created it!)

#if defined (ACE_HAS_THREADS)
  ACE_Recursive_Thread_Mutex lock_;
  // This lock protects access/ops on <process_table_>.
#endif /* ACE_HAS_THREADS */
};

#if defined (__ACE_INLINE__)
#include "ace/Process_Manager.i"
#endif /* __ACE_INLINE__ */

#include "ace/post.h"
#endif /* ACE_PROCESS_MANAGER_H */