types, vm: refactor usage of global variables

Introduce an extensible private TLS context structure and use it within
libucode to store global state such as active object iterators.

This allows using libucode concurrently in multiple threads without
unintentionally sharing global state among them.

Also adjust the signal dispatching setup logic in `uc_vm_init()` to only
enable signal handling if no other VM in the same thread already handles
signals.

Suggested-by: Isaac de Wolff <idewolff@vincitech.nl>
[squash commits, move signal handler vm pointer and object iterator list
 into common extensible TLS context, whitespace and naming adjustments,
 extended signal setup logic]
Signed-off-by: Jo-Philipp Wich <jo@mein.io>

4 files changed, 74 insertions, 48 deletions

diff --git a/include/ucode/types.h b/include/ucode/types.h
index 9cd7cfc..85c3eb8 100644
--- a/include/ucode/types.h
+++ b/include/ucode/types.h
@@ -206,11 +206,6 @@ typedef struct {
 
 uc_declare_vector(uc_resource_types_t, uc_resource_type_t *);
 
-
-/* Object iteration */
-
-extern uc_list_t uc_object_iterators;
-
 typedef struct {
 	uc_list_t list;
 	struct lh_table *table;
@@ -270,6 +265,19 @@ uc_search_path_free(uc_search_path_t *search_path) {
 }
 
 
+/* TLS data */
+
+typedef struct {
+	/* VM owning installed signal handlers */
+	uc_vm_t *signal_handler_vm;
+
+	/* Object iteration */
+	uc_list_t object_iterators;
+} uc_thread_context_t;
+
+__hidden uc_thread_context_t *uc_thread_context_get(void);
+
+
 /* VM definitions */
 
 typedef enum {
diff --git a/tests/custom/03_stdlib/60_gc b/tests/custom/03_stdlib/60_gc
index 28c0d00..44e5d9e 100644
--- a/tests/custom/03_stdlib/60_gc
+++ b/tests/custom/03_stdlib/60_gc
@@ -45,11 +45,11 @@ Returns an object count if the given operation is `count`.
 -- End --
 
 -- Expect stdout --
-Count #1: 6
-Count #2: 7
-Count #3: 6
-Count #4: 7
-Count #5: 6
+Count #1: 5
+Count #2: 6
+Count #3: 5
+Count #4: 6
+Count #5: 5
 -- End --
 
 
@@ -84,24 +84,24 @@ Testing enabling the automatic collector.
 -- End --
 
 -- Expect stdout --
-Count #1: 7
-Count #2: 14
-Count #3: 14
-Count #4: 14
-Count #5: 14
-Count #6: 14
-Count #7: 14
-Count #8: 14
-Count #9: 14
-Count #10: 14
-Count #11: 14
-Count #12: 24
-Count #13: 34
-Count #14: 44
-Count #15: 54
-Count #16: 64
-Count #17: 74
-Count #18: 84
-Count #19: 94
-Count #20: 104
+Count #1: 6
+Count #2: 12
+Count #3: 12
+Count #4: 12
+Count #5: 12
+Count #6: 12
+Count #7: 12
+Count #8: 12
+Count #9: 12
+Count #10: 12
+Count #11: 12
+Count #12: 22
+Count #13: 32
+Count #14: 42
+Count #15: 52
+Count #16: 62
+Count #17: 72
+Count #18: 82
+Count #19: 92
+Count #20: 102
 -- End --
diff --git a/types.c b/types.c
index 8c30614..5dbf6a8 100644
--- a/types.c
+++ b/types.c
@@ -29,11 +29,6 @@
 #include "ucode/vm.h"
 #include "ucode/program.h"
 
-uc_list_t uc_object_iterators = {
-	.prev = &uc_object_iterators,
-	.next = &uc_object_iterators
-};
-
 static char *uc_default_search_path[] = { LIB_SEARCH_PATH };
 
 uc_parse_config_t uc_default_parse_config = {
@@ -898,7 +893,7 @@ ucv_array_length(uc_value_t *uv)
 static void
 ucv_free_object_entry(struct lh_entry *entry)
 {
-	uc_list_foreach(item, &uc_object_iterators) {
+	uc_list_foreach(item, &uc_thread_context_get()->object_iterators) {
 		uc_object_iterator_t *iter = (uc_object_iterator_t *)item;
 
 		if (iter->u.pos == entry)
@@ -955,7 +950,7 @@ ucv_object_add(uc_value_t *uv, const char *key, uc_value_t *val)
 
 		/* insert will rehash table, backup affected iterator states */
 		if (rehash) {
-			uc_list_foreach(item, &uc_object_iterators) {
+			uc_list_foreach(item, &uc_thread_context_get()->object_iterators) {
 				uc_object_iterator_t *iter = (uc_object_iterator_t *)item;
 
 				if (iter->table != object->table)
@@ -979,7 +974,7 @@ ucv_object_add(uc_value_t *uv, const char *key, uc_value_t *val)
 
 		/* restore affected iterator state pointer after rehash */
 		if (rehash) {
-			uc_list_foreach(item, &uc_object_iterators) {
+			uc_list_foreach(item, &uc_thread_context_get()->object_iterators) {
 				uc_object_iterator_t *iter = (uc_object_iterator_t *)item;
 
 				if (iter->table != object->table)
@@ -2481,3 +2476,18 @@ uc_search_path_init(uc_search_path_t *search_path)
 	for (i = 0; i < ARRAY_SIZE(uc_default_search_path); i++)
 		uc_vector_push(search_path, xstrdup(uc_default_search_path[i]));
 }
+
+
+static __thread uc_thread_context_t *tls_ctx;
+
+uc_thread_context_t *
+uc_thread_context_get(void)
+{
+	if (tls_ctx == NULL) {
+		tls_ctx = xalloc(sizeof(*tls_ctx));
+		tls_ctx->object_iterators.prev = &tls_ctx->object_iterators;
+		tls_ctx->object_iterators.next = &tls_ctx->object_iterators;
+	}
+
+	return tls_ctx;
+}
diff --git a/vm.c b/vm.c
index 9488288..ce9c217 100644
--- a/vm.c
+++ b/vm.c
@@ -145,37 +145,44 @@ uc_vm_alloc_global_scope(uc_vm_t *vm)
 static void
 uc_vm_output_exception(uc_vm_t *vm, uc_exception_t *ex);
 
-static uc_vm_t *signal_handler_vm;
-
 static void
 uc_vm_signal_handler(int sig)
 {
-	assert(signal_handler_vm);
+	uc_vm_t *vm = uc_thread_context_get()->signal_handler_vm;
+
+	assert(vm);
 
-	uc_vm_signal_raise(signal_handler_vm, sig);
+	uc_vm_signal_raise(vm, sig);
 }
 
 static void
 uc_vm_signal_handlers_setup(uc_vm_t *vm)
 {
+	uc_thread_context_t *tctx;
+
 	memset(&vm->signal, 0, sizeof(vm->signal));
 
 	vm->signal.sigpipe[0] = -1;
 	vm->signal.sigpipe[1] = -1;
 
-	if (!vm->config->setup_signal_handlers)
+	if (vm->config->setup_signal_handlers)
 		return;
 
-	if (pipe2(vm->signal.sigpipe, O_CLOEXEC | O_NONBLOCK) != 0)
+	tctx = uc_thread_context_get();
+
+	if (tctx->signal_handler_vm)
 		return;
 
-	signal_handler_vm = vm;
+	if (pipe2(vm->signal.sigpipe, O_CLOEXEC | O_NONBLOCK) != 0)
+		return;
 
 	vm->signal.handler = ucv_array_new_length(vm, UC_SYSTEM_SIGNAL_COUNT);
 
 	vm->signal.sa.sa_handler = uc_vm_signal_handler;
 	vm->signal.sa.sa_flags = SA_RESTART | SA_ONSTACK;
 	sigemptyset(&vm->signal.sa.sa_mask);
+
+	tctx->signal_handler_vm = vm;
 }
 
 void uc_vm_init(uc_vm_t *vm, uc_parse_config_t *config)
@@ -778,11 +785,10 @@ uc_vm_exception_tostring(uc_vm_t *vm, size_t nargs)
 	return message ? ucv_get(message) : ucv_string_new("Exception");
 }
 
-static uc_value_t *exception_prototype = NULL;
-
 static uc_value_t *
 uc_vm_exception_new(uc_vm_t *vm, uc_exception_type_t type, const char *message, uc_value_t *stacktrace)
 {
+	uc_value_t *exception_prototype = uc_vm_registry_get(vm, "vm.exception.proto");
 	uc_value_t *exo;
 
 	if (exception_prototype == NULL) {
@@ -790,6 +796,8 @@ uc_vm_exception_new(uc_vm_t *vm, uc_exception_type_t type, const char *message,
 
 		ucv_object_add(exception_prototype, "tostring",
 			ucv_cfunction_new("tostring", uc_vm_exception_tostring));
+
+		uc_vm_registry_set(vm, "vm.exception.proto", exception_prototype);
 	}
 
 	exo = ucv_object_new(vm);
@@ -2222,7 +2230,7 @@ uc_vm_object_iterator_next(uc_vm_t *vm, uc_vm_insn_t insn,
 		iter->table = obj->table;
 		iter->u.pos = obj->table->head;
 
-		uc_list_insert(&uc_object_iterators, &iter->list);
+		uc_list_insert(&uc_thread_context_get()->object_iterators, &iter->list);
 	}
 	else if (ucv_type(k) == UC_RESOURCE &&
 	         res->type == &uc_vm_object_iterator_type && res->data != NULL) {