Known problems with SLY
-----------------------

## Common to all backends

### Caution: network security

The `M-x sly` command has Lisp listen on a TCP socket and wait for
Emacs to connect, which typically takes on the order of one second. If
someone else were to connect to this socket then they could use the
SLY protocol to control the Lisp process.

The listen socket is bound on the loopback interface in all Lisps that
support this. This way remote hosts are unable to connect.

### READ-CHAR-NO-HANG is broken

`READ-CHAR-NO-HANG` doesn't work properly for sly-input-streams.  Due
to the way we request input from Emacs it's not possible to repeatedly
poll for input.  To get any input you have to call `READ-CHAR` (or a
function which calls `READ-CHAR`).

## Backend-specific problems

### CMUCL

The default communication style `:SIGIO` is reportedly unreliable with
certain libraries (like libSDL) and certain platforms (like Solaris on
Sparc). It generally works very well on x86 so it remains the default.

### SBCL

The latest released version of SBCL at the time of packaging should
work.  Older or newer SBCLs may or may not work.  Do not use
multithreading with unpatched 2.4 Linux kernels.  There are also
problems with kernel versions 2.6.5 - 2.6.10.

The (v)iew-source command can only locate exact source forms for code
compiled at (debug 2) or higher. The default level is lower and SBCL
itself is compiled at a lower setting. Thus only defun-granularity is
available with default policies.

### LispWorks

On Windows, SLY hangs when calling foreign functions or certain
other functions.  The reason for this problem is unknown.

We only support latin1 encoding.  (Unicode wouldn't be hard to add.)

### Allegro CL

Interrupting Allegro with C-c C-b can be slow.  This is caused by the
a relatively large process-quantum: 2 seconds by default.  Allegro
responds much faster if `MP:*DEFAULT-PROCESS-QUANTUM*` is set to 0.1.

### CLISP

We require version 2.49 or higher. We also require socket support, so
you may have to start CLISP with `clisp -K full`.

Under Windows, interrupting (with C-c C-b) doesn't work.  Emacs sends
a SIGINT signal, but the signal is either ignored or CLISP exits
immediately.

On Windows, CLISP may refuse to parse filenames like
"C:\\DOCUME~1\\johndoe\\LOCALS~1\\Temp\\sly.1424" when we actually
mean C:\Documents and Settings\johndoe\Local Settings\sly.1424.  As
a workaround, you could set sly-to-lisp-filename-function to some
function that returns a string that is accepted by CLISP.

Function arguments and local variables aren't displayed properly in
the backtrace.  Changes to CLISP's C code are needed to fix this
problem.  Interpreted code is usually easer to debug.

`M-.` (find-definition) only works if the fasl file is in the same
directory as the source file.

The arglist doesn't include the proper names only "fake symbols" like
`arg1`.

### Armed Bear Common Lisp

The ABCL support is still new and experimental.