gdb: Coalesce/aggregate (async) vCont packets/actions

Currently, with "maint set target-non-stop on", that is, when gdb
connects with the non-stop/asynchronous variant of the remote
protocol, even with "set non-stop off", GDB always sends one vCont
packet per thread resumed.  This patch makes GDB aggregate and
coalesce vCont packets, so we send vCont packets like "vCont;s:p1.1;c"
in non-stop mode too.

Basically, this is done by:

  - Adding a new target method target_commit_resume that is called
    after calling target_resume one or more times.  When resuming a
    batch of threads, we'll only call target_commit_resume once after
    calling target_resume for all threads.

  - Making the remote target defer sending the actual vCont packet to
    target_commit_resume.

Special care must be taken to avoid sending a vCont action with a
"wildcard" thread-id (all threads of process / all threads) when that
would resume threads/processes that should not be resumed.  See
remote_commit_resume comments for details.

Unlike all-stop's remote_resume implementation, this handles the case
of too many actions resulting in a too-big vCont packet, by flushing
the vCont packet and starting a new one.

E.g., imagining that the "c" action in:

  vCont;s:1;c

overflows the packet buffer, we split the actions like:

  vCont;s:1
  vCont;c

Tested on x86_64 Fedora 20, with and without "maint set
target-non-stop on".

Also tested with a hack that makes remote_commit_resume flush the vCont
packet after every action appended (which caught a few bugs).

gdb/ChangeLog:
2016-10-26  Pedro Alves  <palves@redhat.com>

	* inferior.h (ALL_NON_EXITED_INFERIORS): New macro.
	* infrun.c (do_target_resume): Call target_commit_resume.
	(proceed): Defer target_commit_resume while looping over threads,
	resuming them.  Call target_commit_resume at the end.
	* record-btrace.c (record_btrace_commit_resume): New function.
	(init_record_btrace_ops): Install it as to_commit_resume method.
	* record-full.c (record_full_commit_resume): New function.
	(record_full_wait_1): Call the beneath target's to_commit_resume
	method.
	(init_record_full_ops): Install record_full_commit_resume as
	to_commit_resume method.
	* remote.c (struct private_thread_info) <last_resume_step,
	last_resume_sig, vcont_resumed>: New fields.
	(remote_add_thread): Set the new thread's vcont_resumed flag.
	(demand_private_info): Delete.
	(get_private_info_thread, get_private_info_ptid): New functions.
	(remote_update_thread_list): Adjust.
	(process_initial_stop_replies): Clear the thread's vcont_resumed
	flag.
	(remote_resume): If connected in non-stop mode, record the resume
	request and return early.
	(struct private_inferior): New.
	(struct vcont_builder): New.
	(vcont_builder_restart, vcont_builder_flush)
	(vcont_builder_push_action): New functions.
	(MAX_ACTION_SIZE): New macro.
	(remote_commit_resume): New function.
	(thread_pending_fork_status, is_pending_fork_parent_thread): New
	functions.
	(check_pending_event_prevents_wildcard_vcont_callback)
	(check_pending_events_prevent_wildcard_vcont): New functions.
	(process_stop_reply): Adjust.  Clear the thread's vcont_resumed
	flag.
	(init_remote_ops): Install remote_commit_resume.
	* target-delegates.c: Regenerate.
	* target.c (defer_target_commit_resume): New global.
	(target_commit_resume, make_cleanup_defer_target_commit_resume):
	New functions.
	* target.h (struct target_ops) <to_commit_resume>: New field.
	(target_resume): Update comments.
	(target_commit_resume): New declaration.

1 files changed, 36 insertions, 11 deletions

diff --git a/gdb/target.h b/gdb/target.h
index 176f332..a54b3db 100644
--- a/gdb/target.h
+++ b/gdb/target.h
@@ -461,6 +461,8 @@ struct target_ops
 		       int TARGET_DEBUG_PRINTER (target_debug_print_step),
 		       enum gdb_signal)
       TARGET_DEFAULT_NORETURN (noprocess ());
+    void (*to_commit_resume) (struct target_ops *)
+      TARGET_DEFAULT_IGNORE ();
     ptid_t (*to_wait) (struct target_ops *,
 		       ptid_t, struct target_waitstatus *,
 		       int TARGET_DEBUG_PRINTER (target_debug_print_options))
@@ -1328,19 +1330,42 @@ extern void target_detach (const char *, int);
 
 extern void target_disconnect (const char *, int);
 
-/* Resume execution of the target process PTID (or a group of
-   threads).  STEP says whether to hardware single-step or to run free;
-   SIGGNAL is the signal to be given to the target, or GDB_SIGNAL_0 for no
-   signal.  The caller may not pass GDB_SIGNAL_DEFAULT.  A specific
-   PTID means `step/resume only this process id'.  A wildcard PTID
-   (all threads, or all threads of process) means `step/resume
-   INFERIOR_PTID, and let other threads (for which the wildcard PTID
-   matches) resume with their 'thread->suspend.stop_signal' signal
-   (usually GDB_SIGNAL_0) if it is in "pass" state, or with no signal
-   if in "no pass" state.  */
-
+/* Resume execution (or prepare for execution) of a target thread,
+   process or all processes.  STEP says whether to hardware
+   single-step or to run free; SIGGNAL is the signal to be given to
+   the target, or GDB_SIGNAL_0 for no signal.  The caller may not pass
+   GDB_SIGNAL_DEFAULT.  A specific PTID means `step/resume only this
+   process id'.  A wildcard PTID (all threads, or all threads of
+   process) means `step/resume INFERIOR_PTID, and let other threads
+   (for which the wildcard PTID matches) resume with their
+   'thread->suspend.stop_signal' signal (usually GDB_SIGNAL_0) if it
+   is in "pass" state, or with no signal if in "no pass" state.
+
+   In order to efficiently handle batches of resumption requests,
+   targets may implement this method such that it records the
+   resumption request, but defers the actual resumption to the
+   target_commit_resume method implementation.  See
+   target_commit_resume below.  */
 extern void target_resume (ptid_t ptid, int step, enum gdb_signal signal);
 
+/* Commit a series of resumption requests previously prepared with
+   target_resume calls.
+
+   GDB always calls target_commit_resume after calling target_resume
+   one or more times.  A target may thus use this method in
+   coordination with the target_resume method to batch target-side
+   resumption requests.  In that case, the target doesn't actually
+   resume in its target_resume implementation.  Instead, it prepares
+   the resumption in target_resume, and defers the actual resumption
+   to target_commit_resume.  E.g., the remote target uses this to
+   coalesce multiple resumption requests in a single vCont packet.  */
+extern void target_commit_resume ();
+
+/* Setup to defer target_commit_resume calls, and return a cleanup
+   that reactivates target_commit_resume, if it was previously
+   active.  */
+struct cleanup *make_cleanup_defer_target_commit_resume ();
+
 /* For target_read_memory see target/target.h.  */
 
 /* The default target_ops::to_wait implementation.  */