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Optionally disallow defining new methods and drop backedges #198

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Optionally disallow defining new methods and drop backedges #198

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4e03fea
Optionally disallow defining new methods and drop backedges
Drvi Nov 14, 2024
a79cee8
Make `allow_new_worlds` atomic
Drvi Nov 14, 2024
917f872
Fixup: also respect `allow_new_world` in `jl_method_table_add_backedge`
Drvi Nov 14, 2024
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47 changes: 47 additions & 0 deletions src/gf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,7 @@
extern "C" {
#endif

static _Atomic(size_t) allow_new_worlds = 1;
JL_DLLEXPORT _Atomic(size_t) jl_world_counter = 1; // uses atomic acquire/release
JL_DLLEXPORT size_t jl_get_world_counter(void) JL_NOTSAFEPOINT
{
Expand Down Expand Up @@ -1718,6 +1719,8 @@ static void invalidate_backedges(void (*f)(jl_code_instance_t*), jl_method_insta
// add a backedge from callee to caller
JL_DLLEXPORT void jl_method_instance_add_backedge(jl_method_instance_t *callee, jl_value_t *invokesig, jl_method_instance_t *caller)
{
if (!jl_atomic_load_acquire(&allow_new_worlds))
return;
JL_LOCK(&callee->def.method->writelock);
if (invokesig == jl_nothing)
invokesig = NULL; // julia uses `nothing` but C uses NULL (#undef)
Expand Down Expand Up @@ -1753,6 +1756,8 @@ JL_DLLEXPORT void jl_method_instance_add_backedge(jl_method_instance_t *callee,
// add a backedge from a non-existent signature to caller
JL_DLLEXPORT void jl_method_table_add_backedge(jl_methtable_t *mt, jl_value_t *typ, jl_value_t *caller)
{
if (!jl_atomic_load_acquire(&allow_new_worlds))
return;
JL_LOCK(&mt->writelock);
if (!mt->backedges) {
// lazy-init the backedges array
Expand Down Expand Up @@ -1915,8 +1920,48 @@ static void jl_method_table_invalidate(jl_methtable_t *mt, jl_typemap_entry_t *m
}
}

static int erase_method_backedges(jl_typemap_entry_t *def, void *closure)
{
jl_method_t *method = def->func.method;
jl_value_t *specializations = jl_atomic_load_relaxed(&method->specializations);
if (jl_is_svec(specializations)) {
size_t i, l = jl_svec_len(specializations);
for (i = 0; i < l; i++) {
jl_method_instance_t *mi = (jl_method_instance_t*)jl_svecref(specializations, i);
if ((jl_value_t*)mi != jl_nothing) {
mi->backedges = NULL;
}
}
}
else {
jl_method_instance_t *mi = (jl_method_instance_t*)specializations;
mi->backedges = NULL;
}
return 1;
}

static int erase_all_backedges(jl_methtable_t *mt, void *env)
{
// removes all method caches
// this might not be entirely safe (GC or MT), thus we only do it very early in bootstrapping
mt->backedges = NULL;
jl_typemap_visitor(jl_atomic_load_relaxed(&mt->defs), erase_method_backedges, env);
return 1;
}

JL_DLLEXPORT void jl_disable_new_worlds(void)
{
if (jl_generating_output())
jl_error("Disabling Method changes is not possible when generating output.");
jl_atomic_store_release(&allow_new_worlds, 0);
jl_foreach_reachable_mtable(erase_all_backedges, (void*)NULL);
}


JL_DLLEXPORT void jl_method_table_disable(jl_methtable_t *mt, jl_method_t *method)
{
if (!jl_atomic_load_acquire(&allow_new_worlds))
jl_error("Method changes have been disabled via a call to jl_disable_new_worlds.");
jl_typemap_entry_t *methodentry = do_typemap_search(mt, method);
JL_LOCK(&mt->writelock);
// Narrow the world age on the method to make it uncallable
Expand Down Expand Up @@ -1986,6 +2031,8 @@ static int is_replacing(char ambig, jl_value_t *type, jl_method_t *m, jl_method_

JL_DLLEXPORT void jl_method_table_insert(jl_methtable_t *mt, jl_method_t *method, jl_tupletype_t *simpletype)
{
if (!jl_atomic_load_acquire(&allow_new_worlds))
jl_error("Method changes have been disabled via a call to jl_disable_new_worlds.");
JL_TIMING(ADD_METHOD, ADD_METHOD);
assert(jl_is_method(method));
assert(jl_is_mtable(mt));
Expand Down
4 changes: 2 additions & 2 deletions src/staticdata.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3447,11 +3447,11 @@ static jl_value_t *jl_restore_package_image_from_stream(void* pkgimage_handle, i
jl_restore_system_image_from_stream_(f, image, depmods, checksum, (jl_array_t**)&restored, &init_order, &extext_methods, &new_specializations, &method_roots_list, &ext_targets, &edges, &base, &ccallable_list, &cachesizes);
JL_SIGATOMIC_END();

// Insert method extensions
jl_insert_methods(extext_methods);
// No special processing of `new_specializations` is required because recaching handled it
// Add roots to methods
jl_copy_roots(method_roots_list, jl_worklist_key((jl_array_t*)restored));
// Insert method extensions
jl_insert_methods(extext_methods);
// Handle edges
size_t world = jl_atomic_load_acquire(&jl_world_counter);
jl_insert_backedges((jl_array_t*)edges, (jl_array_t*)ext_targets, (jl_array_t*)new_specializations, world); // restore external backedges (needs to be last)
Expand Down