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authorLukas Larsson <[email protected]>2014-10-20 17:48:09 +0200
committerLukas Larsson <[email protected]>2014-10-20 17:48:09 +0200
commit70baef6ba7582ab1ea85de40b5c45bed8d14f0b7 (patch)
tree5076d5cf71ae58f03ff628c24b62c9aaf2ff4eed /lib/kernel/src
parentc36765a19f48701c5216bc9eeb305aefe5031c71 (diff)
parent2d3a39b5729a295d4e0ac416ff0280e3edca44c6 (diff)
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Merge branch 'lukas/erts/non-blocking-shell'
* lukas/erts/non-blocking-shell: Fix io:columns/0 timeout when invoked via user kernel,ssh: Add synchronous user_drv protocol erts: Make writing to non-tty fds non-blocking erts: Make tty driver non-blocking
Diffstat (limited to 'lib/kernel/src')
-rw-r--r--lib/kernel/src/group.erl148
-rw-r--r--lib/kernel/src/user_drv.erl131
2 files changed, 180 insertions, 99 deletions
diff --git a/lib/kernel/src/group.erl b/lib/kernel/src/group.erl
index b36dbf33dd..046885f885 100644
--- a/lib/kernel/src/group.erl
+++ b/lib/kernel/src/group.erl
@@ -111,8 +111,13 @@ start_shell1(Fun) ->
server_loop(Drv, Shell, Buf0) ->
receive
{io_request,From,ReplyAs,Req} when is_pid(From) ->
- Buf = io_request(Req, From, ReplyAs, Drv, Buf0),
- server_loop(Drv, Shell, Buf);
+ %% This io_request may cause a transition to a couple of
+ %% selective receive loops elsewhere in this module.
+ Buf = io_request(Req, From, ReplyAs, Drv, Buf0),
+ server_loop(Drv, Shell, Buf);
+ {reply,{{From,ReplyAs},Reply}} ->
+ io_reply(From, ReplyAs, Reply),
+ server_loop(Drv, Shell, Buf0);
{driver_id,ReplyTo} ->
ReplyTo ! {self(),driver_id,Drv},
server_loop(Drv, Shell, Buf0);
@@ -172,10 +177,13 @@ set_unicode_state(Drv,Bool) ->
io_request(Req, From, ReplyAs, Drv, Buf0) ->
- case io_request(Req, Drv, Buf0) of
+ case io_request(Req, Drv, {From,ReplyAs}, Buf0) of
{ok,Reply,Buf} ->
io_reply(From, ReplyAs, Reply),
Buf;
+ {noreply,Buf} ->
+ %% We expect a {reply,_} message from the Drv when request is done
+ Buf;
{error,Reply,Buf} ->
io_reply(From, ReplyAs, Reply),
Buf;
@@ -196,78 +204,85 @@ io_request(Req, From, ReplyAs, Drv, Buf0) ->
%% io_request({put_chars,unicode,Binary}, Drv, Buf) when is_binary(Binary) ->
%% send_drv(Drv, {put_chars,Binary}),
%% {ok,ok,Buf};
-io_request({put_chars,unicode,Chars}, Drv, Buf) ->
+%%
+%% These put requests have to be synchronous to the driver as otherwise
+%% there is no guarantee that the data has actually been printed.
+io_request({put_chars,unicode,Chars}, Drv, From, Buf) ->
case catch unicode:characters_to_binary(Chars,utf8) of
Binary when is_binary(Binary) ->
- send_drv(Drv, {put_chars, unicode, Binary}),
- {ok,ok,Buf};
+ send_drv(Drv, {put_chars_sync, unicode, Binary, {From,ok}}),
+ {noreply,Buf};
_ ->
{error,{error,{put_chars, unicode,Chars}},Buf}
end;
-io_request({put_chars,unicode,M,F,As}, Drv, Buf) ->
+io_request({put_chars,unicode,M,F,As}, Drv, From, Buf) ->
case catch apply(M, F, As) of
Binary when is_binary(Binary) ->
- send_drv(Drv, {put_chars, unicode,Binary}),
- {ok,ok,Buf};
+ send_drv(Drv, {put_chars_sync, unicode, Binary, {From,ok}}),
+ {noreply,Buf};
Chars ->
case catch unicode:characters_to_binary(Chars,utf8) of
B when is_binary(B) ->
- send_drv(Drv, {put_chars, unicode,B}),
- {ok,ok,Buf};
+ send_drv(Drv, {put_chars_sync, unicode, B, {From,ok}}),
+ {noreply,Buf};
_ ->
{error,{error,F},Buf}
end
end;
-io_request({put_chars,latin1,Binary}, Drv, Buf) when is_binary(Binary) ->
- send_drv(Drv, {put_chars, unicode,unicode:characters_to_binary(Binary,latin1)}),
- {ok,ok,Buf};
-io_request({put_chars,latin1,Chars}, Drv, Buf) ->
+io_request({put_chars,latin1,Binary}, Drv, From, Buf) when is_binary(Binary) ->
+ send_drv(Drv, {put_chars_sync, unicode,
+ unicode:characters_to_binary(Binary,latin1),
+ {From,ok}}),
+ {noreply,Buf};
+io_request({put_chars,latin1,Chars}, Drv, From, Buf) ->
case catch unicode:characters_to_binary(Chars,latin1) of
Binary when is_binary(Binary) ->
- send_drv(Drv, {put_chars, unicode,Binary}),
- {ok,ok,Buf};
+ send_drv(Drv, {put_chars_sync, unicode, Binary, {From,ok}}),
+ {noreply,Buf};
_ ->
{error,{error,{put_chars,latin1,Chars}},Buf}
end;
-io_request({put_chars,latin1,M,F,As}, Drv, Buf) ->
+io_request({put_chars,latin1,M,F,As}, Drv, From, Buf) ->
case catch apply(M, F, As) of
Binary when is_binary(Binary) ->
- send_drv(Drv, {put_chars, unicode,unicode:characters_to_binary(Binary,latin1)}),
- {ok,ok,Buf};
+ send_drv(Drv, {put_chars_sync, unicode,
+ unicode:characters_to_binary(Binary,latin1),
+ {From,ok}}),
+ {noreply,Buf};
Chars ->
case catch unicode:characters_to_binary(Chars,latin1) of
B when is_binary(B) ->
- send_drv(Drv, {put_chars, unicode,B}),
- {ok,ok,Buf};
+ send_drv(Drv, {put_chars_sync, unicode, B, {From,ok}}),
+ {noreply,Buf};
_ ->
{error,{error,F},Buf}
end
end;
-io_request({get_chars,Encoding,Prompt,N}, Drv, Buf) ->
+io_request({get_chars,Encoding,Prompt,N}, Drv, _From, Buf) ->
get_chars(Prompt, io_lib, collect_chars, N, Drv, Buf, Encoding);
-io_request({get_line,Encoding,Prompt}, Drv, Buf) ->
+io_request({get_line,Encoding,Prompt}, Drv, _From, Buf) ->
get_chars(Prompt, io_lib, collect_line, [], Drv, Buf, Encoding);
-io_request({get_until,Encoding, Prompt,M,F,As}, Drv, Buf) ->
+io_request({get_until,Encoding, Prompt,M,F,As}, Drv, _From, Buf) ->
get_chars(Prompt, io_lib, get_until, {M,F,As}, Drv, Buf, Encoding);
-io_request({get_password,_Encoding},Drv,Buf) ->
+io_request({get_password,_Encoding},Drv,_From,Buf) ->
get_password_chars(Drv, Buf);
-io_request({setopts,Opts}, Drv, Buf) when is_list(Opts) ->
+io_request({setopts,Opts}, Drv, _From, Buf) when is_list(Opts) ->
setopts(Opts, Drv, Buf);
-io_request(getopts, Drv, Buf) ->
+io_request(getopts, Drv, _From, Buf) ->
getopts(Drv, Buf);
-io_request({requests,Reqs}, Drv, Buf) ->
- io_requests(Reqs, {ok,ok,Buf}, Drv);
+io_request({requests,Reqs}, Drv, From, Buf) ->
+ io_requests(Reqs, {ok,ok,Buf}, From, Drv);
%% New in R12
-io_request({get_geometry,columns},Drv,Buf) ->
+io_request({get_geometry,columns},Drv,_From,Buf) ->
case get_tty_geometry(Drv) of
{W,_H} ->
{ok,W,Buf};
_ ->
{error,{error,enotsup},Buf}
end;
-io_request({get_geometry,rows},Drv,Buf) ->
+io_request({get_geometry,rows},Drv,_From,Buf) ->
case get_tty_geometry(Drv) of
{_W,H} ->
{ok,H,Buf};
@@ -276,38 +291,49 @@ io_request({get_geometry,rows},Drv,Buf) ->
end;
%% BC with pre-R13
-io_request({put_chars,Chars}, Drv, Buf) ->
- io_request({put_chars,latin1,Chars}, Drv, Buf);
-io_request({put_chars,M,F,As}, Drv, Buf) ->
- io_request({put_chars,latin1,M,F,As}, Drv, Buf);
-io_request({get_chars,Prompt,N}, Drv, Buf) ->
- io_request({get_chars,latin1,Prompt,N}, Drv, Buf);
-io_request({get_line,Prompt}, Drv, Buf) ->
- io_request({get_line,latin1,Prompt}, Drv, Buf);
-io_request({get_until, Prompt,M,F,As}, Drv, Buf) ->
- io_request({get_until,latin1, Prompt,M,F,As}, Drv, Buf);
-io_request(get_password,Drv,Buf) ->
- io_request({get_password,latin1},Drv,Buf);
-
-
-
-io_request(_, _Drv, Buf) ->
+io_request({put_chars,Chars}, Drv, From, Buf) ->
+ io_request({put_chars,latin1,Chars}, Drv, From, Buf);
+io_request({put_chars,M,F,As}, Drv, From, Buf) ->
+ io_request({put_chars,latin1,M,F,As}, Drv, From, Buf);
+io_request({get_chars,Prompt,N}, Drv, From, Buf) ->
+ io_request({get_chars,latin1,Prompt,N}, Drv, From, Buf);
+io_request({get_line,Prompt}, Drv, From, Buf) ->
+ io_request({get_line,latin1,Prompt}, Drv, From, Buf);
+io_request({get_until, Prompt,M,F,As}, Drv, From, Buf) ->
+ io_request({get_until,latin1, Prompt,M,F,As}, Drv, From, Buf);
+io_request(get_password,Drv,From,Buf) ->
+ io_request({get_password,latin1},Drv,From,Buf);
+
+
+
+io_request(_, _Drv, _From, Buf) ->
{error,{error,request},Buf}.
-%% Status = io_requests(RequestList, PrevStat, Drv)
-%% Process a list of output requests as long as the previous status is 'ok'.
-
-io_requests([R|Rs], {ok,ok,Buf}, Drv) ->
- io_requests(Rs, io_request(R, Drv, Buf), Drv);
-io_requests([_|_], Error, _Drv) ->
+%% Status = io_requests(RequestList, PrevStat, From, Drv)
+%% Process a list of output requests as long as
+%% the previous status is 'ok' or noreply.
+%%
+%% We use undefined as the From for all but the last request
+%% in order to discards acknowledgements from those requests.
+%%
+io_requests([R|Rs], {noreply,Buf}, From, Drv) ->
+ ReqFrom = if Rs =:= [] -> From; true -> undefined end,
+ io_requests(Rs, io_request(R, Drv, ReqFrom, Buf), From, Drv);
+io_requests([R|Rs], {ok,ok,Buf}, From, Drv) ->
+ ReqFrom = if Rs =:= [] -> From; true -> undefined end,
+ io_requests(Rs, io_request(R, Drv, ReqFrom, Buf), From, Drv);
+io_requests([_|_], Error, _From, _Drv) ->
Error;
-io_requests([], Stat, _) ->
+io_requests([], Stat, _From, _) ->
Stat.
%% io_reply(From, ReplyAs, Reply)
%% The function for sending i/o command acknowledgement.
%% The ACK contains the return value.
+io_reply(undefined, _ReplyAs, _Reply) ->
+ %% Ignore these replies as they are generated from io_requests/4.
+ ok;
io_reply(From, ReplyAs, Reply) ->
From ! {io_reply,ReplyAs,Reply},
ok.
@@ -619,6 +645,10 @@ more_data(What, Cont0, Drv, Ls, Encoding) ->
io_request(Req, From, ReplyAs, Drv, []), %WRONG!!!
send_drv_reqs(Drv, edlin:redraw_line(Cont)),
get_line1({more_chars,Cont,[]}, Drv, Ls, Encoding);
+ {reply,{{From,ReplyAs},Reply}} ->
+ %% We take care of replies from puts here as well
+ io_reply(From, ReplyAs, Reply),
+ more_data(What, Cont0, Drv, Ls, Encoding);
{'EXIT',Drv,interrupt} ->
interrupted;
{'EXIT',Drv,_} ->
@@ -641,6 +671,10 @@ get_line_echo_off1({Chars,[]}, Drv) ->
{io_request,From,ReplyAs,Req} when is_pid(From) ->
io_request(Req, From, ReplyAs, Drv, []),
get_line_echo_off1({Chars,[]}, Drv);
+ {reply,{{From,ReplyAs},Reply}} when From =/= undefined ->
+ %% We take care of replies from puts here as well
+ io_reply(From, ReplyAs, Reply),
+ get_line_echo_off1({Chars,[]},Drv);
{'EXIT',Drv,interrupt} ->
interrupted;
{'EXIT',Drv,_} ->
@@ -790,6 +824,10 @@ get_password1({Chars,[]}, Drv) ->
%% set to []. But do we expect anything but plain output?
get_password1({Chars, []}, Drv);
+ {reply,{{From,ReplyAs},Reply}} ->
+ %% We take care of replies from puts here as well
+ io_reply(From, ReplyAs, Reply),
+ get_password1({Chars, []},Drv);
{'EXIT',Drv,interrupt} ->
interrupted;
{'EXIT',Drv,_} ->
diff --git a/lib/kernel/src/user_drv.erl b/lib/kernel/src/user_drv.erl
index a91c23539d..e6ce85c379 100644
--- a/lib/kernel/src/user_drv.erl
+++ b/lib/kernel/src/user_drv.erl
@@ -29,6 +29,7 @@
-define(OP_INSC,2).
-define(OP_DELC,3).
-define(OP_BEEP,4).
+-define(OP_PUTC_SYNC,5).
% Control op
-define(CTRL_OP_GET_WINSIZE,100).
-define(CTRL_OP_GET_UNICODE_STATE,101).
@@ -133,7 +134,7 @@ server1(Iport, Oport, Shell) ->
[erlang:system_info(system_version)]))},
Iport, Oport),
%% Enter the server loop.
- server_loop(Iport, Oport, Curr, User, Gr).
+ server_loop(Iport, Oport, Curr, User, Gr, queue:new()).
rem_sh_opts(Node) ->
[{expand_fun,fun(B)-> rpc:call(Node,edlin_expand,expand,[B]) end}].
@@ -158,42 +159,41 @@ start_user() ->
User
end.
-server_loop(Iport, Oport, User, Gr) ->
+server_loop(Iport, Oport, User, Gr, IOQueue) ->
Curr = gr_cur_pid(Gr),
put(current_group, Curr),
- server_loop(Iport, Oport, Curr, User, Gr).
+ server_loop(Iport, Oport, Curr, User, Gr, IOQueue).
-server_loop(Iport, Oport, Curr, User, Gr) ->
+server_loop(Iport, Oport, Curr, User, Gr, IOQueue) ->
receive
{Iport,{data,Bs}} ->
BsBin = list_to_binary(Bs),
Unicode = unicode:characters_to_list(BsBin,utf8),
- port_bytes(Unicode, Iport, Oport, Curr, User, Gr);
+ port_bytes(Unicode, Iport, Oport, Curr, User, Gr, IOQueue);
{Iport,eof} ->
Curr ! {self(),eof},
- server_loop(Iport, Oport, Curr, User, Gr);
- {User,Req} -> % never block from user!
- io_request(Req, Iport, Oport),
- server_loop(Iport, Oport, Curr, User, Gr);
- {Curr,tty_geometry} ->
- Curr ! {self(),tty_geometry,get_tty_geometry(Iport)},
- server_loop(Iport, Oport, Curr, User, Gr);
- {Curr,get_unicode_state} ->
- Curr ! {self(),get_unicode_state,get_unicode_state(Iport)},
- server_loop(Iport, Oport, Curr, User, Gr);
- {Curr,set_unicode_state, Bool} ->
- Curr ! {self(),set_unicode_state,set_unicode_state(Iport,Bool)},
- server_loop(Iport, Oport, Curr, User, Gr);
- {Curr,Req} ->
- io_request(Req, Iport, Oport),
- server_loop(Iport, Oport, Curr, User, Gr);
+ server_loop(Iport, Oport, Curr, User, Gr, IOQueue);
+ Req when element(1,Req) =:= User orelse element(1,Req) =:= Curr,
+ tuple_size(Req) =:= 2 orelse tuple_size(Req) =:= 3 ->
+ %% We match {User|Curr,_}|{User|Curr,_,_}
+ NewQ = handle_req(Req, Iport, Oport, IOQueue),
+ server_loop(Iport, Oport, Curr, User, Gr, NewQ);
+ {Oport,ok} ->
+ %% We get this ok from the port, in io_request we store
+ %% info about where to send reply at head of queue
+ {{value,{Origin,Reply}},ReplyQ} = queue:out(IOQueue),
+ Origin ! {reply,Reply},
+ NewQ = handle_req(next, Iport, Oport, ReplyQ),
+ server_loop(Iport, Oport, Curr, User, Gr, NewQ);
{'EXIT',Iport,_R} ->
- server_loop(Iport, Oport, Curr, User, Gr);
+ server_loop(Iport, Oport, Curr, User, Gr, IOQueue);
{'EXIT',Oport,_R} ->
- server_loop(Iport, Oport, Curr, User, Gr);
+ server_loop(Iport, Oport, Curr, User, Gr, IOQueue);
+ {'EXIT',User,shutdown} -> % force data to port
+ server_loop(Iport, Oport, Curr, User, Gr, IOQueue);
{'EXIT',User,_R} -> % keep 'user' alive
NewU = start_user(),
- server_loop(Iport, Oport, Curr, NewU, gr_set_num(Gr, 1, NewU, {}));
+ server_loop(Iport, Oport, Curr, NewU, gr_set_num(Gr, 1, NewU, {}), IOQueue);
{'EXIT',Pid,R} -> % shell and group leader exit
case gr_cur_pid(Gr) of
Pid when R =/= die ,
@@ -213,18 +213,51 @@ server_loop(Iport, Oport, Curr, User, Gr) ->
{ok,Gr2} = gr_set_cur(gr_set_num(Gr1, Ix, Pid1,
{shell,start,Params}), Ix),
put(current_group, Pid1),
- server_loop(Iport, Oport, Pid1, User, Gr2);
+ server_loop(Iport, Oport, Pid1, User, Gr2, IOQueue);
_ -> % remote shell
io_requests([{put_chars,unicode,"(^G to start new job) ***\n"}],
Iport, Oport),
- server_loop(Iport, Oport, Curr, User, Gr1)
+ server_loop(Iport, Oport, Curr, User, Gr1, IOQueue)
end;
_ -> % not current, just remove it
- server_loop(Iport, Oport, Curr, User, gr_del_pid(Gr, Pid))
+ server_loop(Iport, Oport, Curr, User, gr_del_pid(Gr, Pid), IOQueue)
end;
_X ->
%% Ignore unknown messages.
- server_loop(Iport, Oport, Curr, User, Gr)
+ server_loop(Iport, Oport, Curr, User, Gr, IOQueue)
+ end.
+
+%% We always handle geometry and unicode requests
+handle_req({Curr,tty_geometry},Iport,_Oport,IOQueue) ->
+ Curr ! {self(),tty_geometry,get_tty_geometry(Iport)},
+ IOQueue;
+handle_req({Curr,get_unicode_state},Iport,_Oport,IOQueue) ->
+ Curr ! {self(),get_unicode_state,get_unicode_state(Iport)},
+ IOQueue;
+handle_req({Curr,set_unicode_state, Bool},Iport,_Oport,IOQueue) ->
+ Curr ! {self(),set_unicode_state,set_unicode_state(Iport,Bool)},
+ IOQueue;
+handle_req(next,Iport,Oport,IOQueue) ->
+ case queue:out(IOQueue) of
+ {{value,Next},ExecQ} ->
+ NewQ = handle_req(Next,Iport,Oport,queue:new()),
+ queue:join(NewQ,ExecQ);
+ {empty,_} ->
+ IOQueue
+ end;
+handle_req(Msg,Iport,Oport,IOQueue) ->
+ case queue:peek(IOQueue) of
+ empty ->
+ {Origin,Req} = Msg,
+ case io_request(Req, Iport, Oport) of
+ ok -> IOQueue;
+ Reply ->
+ %% Push reply info to front of queue
+ queue:in_r({Origin,Reply},IOQueue)
+ end;
+ _Else ->
+ %% All requests are queued when we have outstanding sync put_chars
+ queue:in(Msg,IOQueue)
end.
%% port_bytes(Bytes, InPort, OutPort, CurrentProcess, UserProcess, Group)
@@ -232,34 +265,34 @@ server_loop(Iport, Oport, Curr, User, Gr) ->
%% either escape to switch_loop or restart the shell. Otherwise send
%% the bytes to Curr.
-port_bytes([$\^G|_Bs], Iport, Oport, _Curr, User, Gr) ->
- handle_escape(Iport, Oport, User, Gr);
+port_bytes([$\^G|_Bs], Iport, Oport, _Curr, User, Gr, IOQueue) ->
+ handle_escape(Iport, Oport, User, Gr, IOQueue);
-port_bytes([$\^C|_Bs], Iport, Oport, Curr, User, Gr) ->
- interrupt_shell(Iport, Oport, Curr, User, Gr);
+port_bytes([$\^C|_Bs], Iport, Oport, Curr, User, Gr, IOQueue) ->
+ interrupt_shell(Iport, Oport, Curr, User, Gr, IOQueue);
-port_bytes([B], Iport, Oport, Curr, User, Gr) ->
+port_bytes([B], Iport, Oport, Curr, User, Gr, IOQueue) ->
Curr ! {self(),{data,[B]}},
- server_loop(Iport, Oport, Curr, User, Gr);
-port_bytes(Bs, Iport, Oport, Curr, User, Gr) ->
+ server_loop(Iport, Oport, Curr, User, Gr, IOQueue);
+port_bytes(Bs, Iport, Oport, Curr, User, Gr, IOQueue) ->
case member($\^G, Bs) of
true ->
- handle_escape(Iport, Oport, User, Gr);
+ handle_escape(Iport, Oport, User, Gr, IOQueue);
false ->
Curr ! {self(),{data,Bs}},
- server_loop(Iport, Oport, Curr, User, Gr)
+ server_loop(Iport, Oport, Curr, User, Gr, IOQueue)
end.
-interrupt_shell(Iport, Oport, Curr, User, Gr) ->
+interrupt_shell(Iport, Oport, Curr, User, Gr, IOQueue) ->
case gr_get_info(Gr, Curr) of
undefined ->
ok; % unknown
_ ->
exit(Curr, interrupt)
end,
- server_loop(Iport, Oport, Curr, User, Gr).
+ server_loop(Iport, Oport, Curr, User, Gr, IOQueue).
-handle_escape(Iport, Oport, User, Gr) ->
+handle_escape(Iport, Oport, User, Gr, IOQueue) ->
case application:get_env(stdlib, shell_esc) of
{ok,abort} ->
Pid = gr_cur_pid(Gr),
@@ -278,11 +311,11 @@ handle_escape(Iport, Oport, User, Gr) ->
Pid1 = group:start(self(), {shell,start,[]}),
io_request({put_chars,unicode,"\n"}, Iport, Oport),
server_loop(Iport, Oport, User,
- gr_add_cur(Gr1, Pid1, {shell,start,[]}));
+ gr_add_cur(Gr1, Pid1, {shell,start,[]}), IOQueue);
_ -> % {ok,jcl} | undefined
io_request({put_chars,unicode,"\nUser switch command\n"}, Iport, Oport),
- server_loop(Iport, Oport, User, switch_loop(Iport, Oport, Gr))
+ server_loop(Iport, Oport, User, switch_loop(Iport, Oport, Gr), IOQueue)
end.
switch_loop(Iport, Oport, Gr) ->
@@ -492,9 +525,12 @@ set_unicode_state(Iport, Bool) ->
io_request(Request, Iport, Oport) ->
try io_command(Request) of
- Command ->
+ {command,_} = Command ->
Oport ! {self(),Command},
- ok
+ ok;
+ {Command,Reply} ->
+ Oport ! {self(),Command},
+ Reply
catch
{requests,Rs} ->
io_requests(Rs, Iport, Oport);
@@ -511,6 +547,13 @@ io_requests([], _Iport, _Oport) ->
put_int16(N, Tail) ->
[(N bsr 8)band 255,N band 255|Tail].
+%% When a put_chars_sync command is used, user_drv guarantees that
+%% the bytes have been put in the buffer of the port before an acknowledgement
+%% is sent back to the process sending the request. This command was added in
+%% OTP 18 to make sure that data sent from io:format is actually printed
+%% to the console before the vm stops when calling erlang:halt(integer()).
+io_command({put_chars_sync, unicode,Cs,Reply}) ->
+ {{command,[?OP_PUTC_SYNC|unicode:characters_to_binary(Cs,utf8)]},Reply};
io_command({put_chars, unicode,Cs}) ->
{command,[?OP_PUTC|unicode:characters_to_binary(Cs,utf8)]};
io_command({move_rel,N}) ->