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author | José Valim <jose.valim@plataformatec.com.br> | 2014-05-01 17:44:18 +0200 |
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committer | Lukas Larsson <lukas@erlang-solutions.com> | 2014-10-16 17:56:17 +0200 |
commit | 2d3a39b5729a295d4e0ac416ff0280e3edca44c6 (patch) | |
tree | 4d3af1051e0b8993bf1e629a628705dc94e0300a /lib/kernel | |
parent | 48083e54b502afb2768066394074d29423162dc8 (diff) | |
download | otp-2d3a39b5729a295d4e0ac416ff0280e3edca44c6.tar.gz otp-2d3a39b5729a295d4e0ac416ff0280e3edca44c6.tar.bz2 otp-2d3a39b5729a295d4e0ac416ff0280e3edca44c6.zip |
Fix io:columns/0 timeout when invoked via user
This patch fixes an issue where io:columns/0 times out when invoked from
any application callback (or any supervisor/supervised module since the
group leader is inherited).
To reproduce the issue, one must simply call io:columns() from any
application callback. You will notice the process will block for 2 seconds
which then times out and returns {:error, :enotsup}.
Note this bug only happens inside the erlang shell (using -noshell or
escripts do not trigger the bug).
To fix the bug, it is important to understand how io requests flow from
application callback processes. Here are the steps followed:
1. Since io:columns/1 is timing out, the first step is to find out who is the
group leader for the application callback process. Using process_info/1, we
can see the parent process is the application_master and handles
io_requests by delegating them to the group_leader.
2. By inspecting the application_master process, we can find the group_leader
the message is sent is the registered process named user. The process is
running the group module which does handle io:columns/1 requests delegating
them to user_drv process.
3. The user_drv process does handle tty_geometry requests, except that a
clause above ends up short-circuiting all tty_geometry requests from the
user process.
This patch moves the user clause below the specific driver messages.
OTP-12241
Diffstat (limited to 'lib/kernel')
-rw-r--r-- | lib/kernel/src/user_drv.erl | 5 |
1 files changed, 0 insertions, 5 deletions
diff --git a/lib/kernel/src/user_drv.erl b/lib/kernel/src/user_drv.erl index 79f80f6604..e6ce85c379 100644 --- a/lib/kernel/src/user_drv.erl +++ b/lib/kernel/src/user_drv.erl @@ -173,11 +173,6 @@ server_loop(Iport, Oport, Curr, User, Gr, IOQueue) -> {Iport,eof} -> Curr ! {self(),eof}, server_loop(Iport, Oport, Curr, User, Gr, IOQueue); - {User,Req} when element(1,Req) == tty_geometry; - element(1,Req) == get_unicode_state; - element(1,Req) == set_unicode_state -> - %% We ignore these requests from User, could be a bug? - 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,_,_} |