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3.2.3 Saving a Core Image

SBCL has the ability to save its state as a file for later execution. This functionality is important for its bootstrapping process, and is also provided as an extension to the user.

— Function: sb-ext:save-lisp-and-die core-file-name &key toplevel executable save-runtime-options purify root-structures environment-name

Save a "core image", i.e. enough information to restart a Lisp process later in the same state, in the file of the specified name. Only global state is preserved: the stack is unwound in the process.

The following &key arguments are defined:

:toplevel
The function to run when the created core file is resumed. The default function handles command line toplevel option processing and runs the top level read-eval-print loop. This function returning is equivalent to (SB-EXT:QUIT :unix-status 0) being called.
:executable
If true, arrange to combine the sbcl runtime and the core image to create a standalone executable. If false (the default), the core image will not be executable on its own. Executable images always behave as if they were passed the –noinform runtime option.
:save-runtime-options
If true, values of runtime options –dynamic-space-size and –control-stack-size that were used to start sbcl are stored in the standalone executable, and restored when the executable is run. This also inhibits normal runtime option processing, causing all command line arguments to be passed to the toplevel. Meaningless if :executable is nil.
:purify
If true (the default on cheneygc), do a purifying gc which moves all dynamically allocated objects into static space. This takes somewhat longer than the normal gc which is otherwise done, but it's only done once, and subsequent GC's will be done less often and will take less time in the resulting core file. See the purify function. This parameter has no effect on platforms using the generational garbage collector.
:root-structures
This should be a list of the main entry points in any newly loaded systems. This need not be supplied, but locality and/or gc performance may be better if they are. Meaningless if :purify is nil. See the purify function.
:environment-name
This is also passed to the purify function when :purify is t. (rarely used)

The save/load process changes the values of some global variables:

*standard-output*, *debug-io*, etc.
Everything related to open streams is necessarily changed, since the os won't let us preserve a stream across save and load.
*default-pathname-defaults*
This is reinitialized to reflect the working directory where the saved core is loaded.

save-lisp-and-die interacts with sb-alien:load-shared-object: see its documentation for details.

On threaded platforms only a single thread may remain running after sb-ext:*save-hooks* have run. Applications using multiple threads can be save-lisp-and-die friendly by registering a save-hook that quits any additional threads, and an init-hook that restarts them.

This implementation is not as polished and painless as you might like:

This isn't because we like it this way, but just because there don't seem to be good quick fixes for either limitation and no one has been sufficiently motivated to do lengthy fixes.

— Variable: sb-ext:*save-hooks*

This is a list of functions which are called in an unspecified order before creating a saved core image. Unused by sbcl itself: reserved for user and applications.

To facilitate distribution of SBCL applications using external resources, the filesystem location of the SBCL core file being used is available from Lisp.

— Variable: sb-ext:*core-pathname*

The absolute pathname of the running sbcl core.