comments

1 files changed, 23 insertions, 5 deletions

diff --git a/coroutine.c b/coroutine.c
index 9a53731..50e4135 100644
--- a/coroutine.c
+++ b/coroutine.c
@@ -5,7 +5,7 @@
  */
 
 #include <stdint.h> /* for uint8_t */
-#include <stdio.h>  /* for fprintf(), stderr */
+#include <stdio.h>  /* for printf(), fprintf(), stderr */
 #include <stdlib.h> /* for calloc(), free() */
 #include <assert.h>
 #include <setjmp.h>
@@ -104,6 +104,9 @@
  *   and a few bytes.
  */
 
+static jmp_buf coroutine_add_env;
+static jmp_buf coroutine_main_env;
+
 enum coroutine_state {
 	CR_NONE = 0,     /* this slot in the table is empty */
 	CR_INITIALIZING, /* running, before cr_begin() */
@@ -112,6 +115,23 @@ enum coroutine_state {
 	CR_PAUSED,       /* not running, and not runnable */ 
 };
 
+/*
+ * Invariants (and non-invariants):
+ *
+ * - exactly 0 or 1 coroutines have state CR_INITIALIZING
+ * - exactly 0 or 1 coroutines have state CR_RUNNING
+ * - if coroutine_running is not zero, then
+ *   coroutine_table[coroutine_running-1] is the currently-running
+ *   coroutine
+ * - the coroutine_running coroutine either has state CR_RUNNING or
+ *   CR_INITIALIZNG
+ * - a coroutine having state CR_RUNNING does *not* imply that
+ *   coroutine_running points at that coroutine; if that coroutine is
+ *   in the middle of coroutine_add(), it coroutine_running points at
+ *   the CR_INITIALIZING child coroutine, while leaving the parent
+ *   coroutine as CR_RUNNING.
+ */
+
 struct coroutine {
 	enum coroutine_state state;
 	jmp_buf              env;
@@ -121,8 +141,6 @@ struct coroutine {
 
 static struct coroutine coroutine_table[COROUTINE_NUM] = {0};
 static cid_t            coroutine_running              = 0;
-static jmp_buf          coroutine_add_env;
-static jmp_buf          coroutine_main_env;
 
 static void call_with_stack(void *stack, cr_fn_t fn, void *args) {
 	static void *saved_sp = NULL;
@@ -247,7 +265,7 @@ bool cr_begin(void) {
 static inline __attribute__ ((no_split_stack)) void _cr_transition(enum coroutine_state state) {
 	assert(coroutine_running && coroutine_table[coroutine_running-1].state == CR_RUNNING);
 	coroutine_table[coroutine_running-1].state = state;
-	if (!setjmp(coroutine_table[coroutine_running-1].env))  /* point=c2 */
+	if (!setjmp(coroutine_table[coroutine_running-1].env)) /* point=c2 */
 		longjmp(coroutine_main_env, 1); /* jump to point=b */
 }
 
@@ -261,7 +279,7 @@ void cr_exit(void) {
 }
 
 void cr_unpause(cid_t cid) {
-	assert(coroutine_table[cid-1].state == CR_PAUSED);
+	assert(cid && coroutine_table[cid-1].state == CR_PAUSED);
 	coroutine_table[cid-1].state = CR_RUNNABLE;
 }