add exit_save_sysimage

Author: IanButterworth

base/Base.jl

@@ -391,6 +391,7 @@ include("loading.jl")
 # misc useful functions & macros
 include("timing.jl")
 include("util.jl")
+include("output.jl")
 
 include("asyncmap.jl")
 

base/output.jl

@@ -0,0 +1,15 @@
+# This file is a part of Julia. License is MIT: https://julialang.org/license
+
+"""
+    exit_save_sysimage(fpath::String)
+
+Save the current state as a sysimage. The sysimage is saved after julia exit, which this
+function triggers.
+"""
+function exit_save_sysimage(fpath::String)
+    fpath = abspath(fpath)
+    ccall(:jl_options_set_outputo, Cvoid, (Cstring,), fpath)
+    ccall(:jl_restore_module_init_order_cache, Cvoid, ())
+    @info "Julia exiting. A sysimage will be generated at $(repr(fpath))"
+    exit()
+end

src/init.c

@@ -44,6 +44,13 @@ extern BOOL (WINAPI *hSymRefreshModuleList)(HANDLE);
 
 // list of modules being deserialized with __init__ methods
 jl_array_t *jl_module_init_order;
+jl_array_t *jl_module_init_order_cache;
+
+JL_DLLEXPORT void jl_restore_module_init_order_cache(void)
+{
+    jl_module_init_order = jl_module_init_order_cache;
+}
+
 
 JL_DLLEXPORT size_t jl_page_size;
 
@@ -771,6 +778,7 @@ static NOINLINE void _finish_julia_init(JL_IMAGE_SEARCH rel, jl_ptls_t ptls, jl_
     if (jl_options.image_file && (!jl_generating_output() || jl_options.incremental) && jl_module_init_order) {
         jl_array_t *init_order = jl_module_init_order;
         JL_GC_PUSH1(&init_order);
+        jl_module_init_order_cache = jl_module_init_order; // used when output is requested later than init
         jl_module_init_order = NULL;
         int i, l = jl_array_len(init_order);
         for (i = 0; i < l; i++) {

src/precompile.c

@@ -22,7 +22,7 @@ JL_DLLEXPORT int jl_generating_output(void)
 
 static void *jl_precompile(int all);
 
-void jl_write_compiler_output(void)
+JL_DLLEXPORT void jl_write_compiler_output(void)
 {
     if (!jl_generating_output()) {
         return;
@@ -36,7 +36,6 @@ void jl_write_compiler_output(void)
         jl_printf(JL_STDERR, "WARNING: --output requested, but no modules defined during run\n");
         return;
     }
-
     jl_array_t *worklist = jl_module_init_order;
     JL_GC_PUSH1(&worklist);
     jl_module_init_order = jl_alloc_vec_any(0);
@@ -110,6 +109,11 @@ void jl_write_compiler_output(void)
     JL_GC_POP();
 }
 
+JL_DLLEXPORT void jl_options_set_outputo(const char * path)
+{
+    jl_options.outputo = path;
+}
+
 // f{<:Union{...}}(...) is a common pattern
 // and expanding the Union may give a leaf function
 static void _compile_all_tvar_union(jl_value_t *methsig)