[dos,js] Try to add own timer ISR

The goal is to check if js scripts do not execute too long under DOS.
It may be buggy.

src/ecmascript/quickjs/heartbeat.c

@@ -44,7 +44,7 @@ js_heartbeat_callback(JSRuntime *rt, void *opaque)
 /* Callback for SIGVTALRM.  Go through all heartbeats, decrease each
  * one's TTL, and call JS_RequestInterruptCallback if a heartbeat's TTL
  * goes to 0. */
-static void
+void
 check_heartbeats(void *data)
 {
 	struct heartbeat *hb;
@@ -67,9 +67,7 @@ check_heartbeats(void *data)
 			}
 		}
 	}
-#ifdef CONFIG_OS_DOS
-	install_signal_handler(SIGALRM, check_heartbeats, NULL, 1);
-#else
+#ifndef CONFIG_OS_DOS
 	install_signal_handler(SIGVTALRM, check_heartbeats, NULL, 1);
 #endif
 }
@@ -95,25 +93,18 @@ add_heartbeat(struct ecmascript_interpreter *interpreter)
 	hb->interpreter = interpreter;
 	add_to_list(heartbeats, hb);
 
+#ifndef CONFIG_OS_DOS
 	/* Update the heartbeat timer. */
 	if (list_is_singleton(*hb)) {
 		heartbeat_timer.it_value.tv_sec = 1;
-#ifdef CONFIG_OS_DOS
-		setitimer(ITIMER_REAL, &heartbeat_timer, NULL);
-#else
 		setitimer(ITIMER_VIRTUAL, &heartbeat_timer, NULL);
-#endif
 	}
 
 	/* We install the handler every call to add_heartbeat instead of only on
 	 * module initialisation because other code may set other handlers for
 	 * the signal.  */
-#ifdef CONFIG_OS_DOS
-	install_signal_handler(SIGALRM, check_heartbeats, NULL, 1);
-#else
 	install_signal_handler(SIGVTALRM, check_heartbeats, NULL, 1);
 #endif
-
 	return hb;
 }
 
@@ -124,15 +115,13 @@ done_heartbeat(struct heartbeat *hb)
 	if (!hb) return; /* add_heartbeat returned NULL */
 	assert(hb->interpreter);
 
+#ifndef CONFIG_OS_DOS
 	/* Stop the heartbeat timer if this heartbeat is the only one. */
 	if (list_is_singleton(*hb)) {
 		heartbeat_timer.it_value.tv_sec = 0;
-#ifdef CONFIG_OS_DOS
-		setitimer(ITIMER_REAL, &heartbeat_timer, NULL);
-#else
 		setitimer(ITIMER_VIRTUAL, &heartbeat_timer, NULL);
-#endif
 	}
+#endif
 
 	del_from_list(hb);
 	hb->interpreter->heartbeat = NULL;

src/ecmascript/quickjs/heartbeat.h

@@ -15,6 +15,7 @@ struct heartbeat {
 };
 
 struct heartbeat *add_heartbeat(struct ecmascript_interpreter *interpreter);
+void check_heartbeats(void *data);
 void done_heartbeat(struct heartbeat *hb);
 int js_heartbeat_callback(JSRuntime *rt, void *opaque);
 

src/osdep/dos/dos.c

@@ -24,6 +24,9 @@
 #include <time.h>
 #include <unistd.h>
 #include <values.h>
+#ifdef CONFIG_ECMASCRIPT
+#include "ecmascript/quickjs/heartbeat.h"
+#endif
 #include "intl/libintl.h"
 #include "main/main.h"
 #include "main/select.h"
@@ -1010,6 +1013,33 @@ void os_seed_random(unsigned char **pool, int *pool_size)
 	*pool_size = RANDOM_POOL_SIZE;
 }
 
+_go32_dpmi_seginfo OldISR, NewISR;
+#define TIMER 8
+//Simple Example of chaining interrupt handlers
+//Adopted from Matthew Mastracci's code
+
+#include <pc.h>
+#include <dpmi.h>
+#include <go32.h>
+
+//macros by Shawn Hargreaves from the Allegro library for locking
+//functions and variables.
+#define LOCK_VARIABLE(x)    _go32_dpmi_lock_data((void *)&x,(long)sizeof(x));
+#define LOCK_FUNCTION(x)    _go32_dpmi_lock_code(x,(long)sizeof(x));
+
+static void
+TickHandler(void)
+{
+#ifdef CONFIG_ECMASCRIPT
+	static int internal = 0;
+
+	if (internal++ >= 19) {
+		internal = 0;
+		check_heartbeats(NULL);
+	}
+#endif
+}
+
 void init_osdep(void)
 {
 	int s, rs;
@@ -1040,12 +1070,27 @@ void init_osdep(void)
 	sigemptyset(&sa.sa_mask);
 	sa.sa_flags = SA_RESTART;
 	EINTRLOOP(rs, sigaction(SIGINT, &sa, NULL));
+
+	LOCK_FUNCTION(TickHandler);
+	LOCK_FUNCTION(check_heartbeats);
+//load the address of the old timer ISR into the OldISR structure
+	_go32_dpmi_get_protected_mode_interrupt_vector(TIMER, &OldISR);
+//point NewISR to the proper selector:offset for handler
+//function
+	NewISR.pm_offset = (int)TickHandler;
+	NewISR.pm_selector = _go32_my_cs();
+//chain the new ISR onto the old one so that first the old
+//timer ISR
+//will be called, then the new timer ISR
+	_go32_dpmi_chain_protected_mode_interrupt_vector(TIMER, &NewISR);
 }
 
 void terminate_osdep(void)
 {
 	if (screen_backbuffer)
 		mem_free(screen_backbuffer);
+
+	_go32_dpmi_set_protected_mode_interrupt_vector(TIMER, &OldISR);
 }
 
 #define LINKS_BIN_SEARCH(entries, eq, ab, key, result)                        \