rtlib: dos: optional run-time replacement of usleep

- control call of __dpmi_yield() to prevent crashes under some dos extenders in dosbox
- add extern  __fb_dos_no_dpmi_yield  to control calling of __dpmi_yield()
- set __fb_dos_no_dpmi_yield = 1 from user program to call usleep_private() internally
  instead of the usual usleep()
- see example in ./examples/DOS/gfxsleep.bas

changelog.txt

@@ -65,6 +65,7 @@ Version 1.10.0
 - In normal build of fbc, try to automatically use gcc to query the search path for a std c++ library.  This helps with dependency for tests/cpp and for some users that want to interop with c++
 - Add  makefile option DISABLE_STDCXX_PATH to disable usnig gcc to search for some c++ library path
 - fbc: allow typename.member symbol checks for #ifdef / #ifndef / defined() where member can be a data field, static data field, nested type, constructor, destructor, property, operator (self-assignment, new, new[], delete, delete[], let, cast, for, step, next), or member procedure.
+- rtlib: dos: add "__fb_dos_no_dpmi_yield" variable to control calling "__dpmi_yield()" and prevent a crash under some dos extenders in dosbox
 
 [fixed]
 - gas64: missing restoring of use of one virtual register on sqr for float (SARG)

examples/DOS/gfxsleep.bas

@@ -0,0 +1,57 @@
+#include once "fbgfx.bi"
+
+extern "c"
+	extern as unsigned long __fb_dos_no_dpmi_yield
+end extern
+
+'' tells SLEEP to call usleep_private() which does not yeild to dpmi
+'' this prevents djgpp c runtime from call __dmpi_yeild() during a
+'' call in SLEEP.  Disabling this behaviour appears to prevent the
+'' program from crashing at least in dosbox with some extenders.
+
+__fb_dos_no_dpmi_yield = 1
+
+screen 13
+
+dim as long w, h
+ScreenControl fb.GET_SCREEN_SIZE, w, h
+
+dim as single maxtime = 100
+dim as single x = 10, y = 10, dx = 50, dy = 0, r = 10
+dim as double t0 = timer, t1 = t0, t2 = 0, td = 0.0001
+dim as string k
+
+do while( t1 - t0 < maxtime ) 
+
+	k = inkey
+	select case k
+	case chr(27)
+		exit do
+	end select
+
+	dy += td * 200
+	x += dx * td
+	y += dy * td
+
+	if( (dx > 0) and (x > w - r) ) then
+		dx *= -1
+	elseif( (dx < 0) and (x < r) ) then
+		dx *= -1
+	end if
+
+	if( (dy > 0) and (y > h - r - r) ) then
+		dy *= -1 * 0.9
+	end if
+
+	circle ( x, y ), r
+
+	sleep 15, 1
+
+	t2 = timer
+	td = t2 - t1
+	t1 =t2
+loop
+
+cls
+print "exiting"
+sleep 1000, 1

src/rtlib/dos/symb_reg.txt

@@ -467,6 +467,7 @@ extern_asm(_fb_Now);
 extern_asm(_fb_ConsoleGetTopRow);
 extern_asm(_fb_OCTEx_b);
 extern_asm(_fb_SetDate);
+extern_asm(___fb_dos_no_dpmi_yield);
 extern_asm(_fb_WstrHexEx_l);
 extern_asm(_fb_DatePart);
 extern_asm(_fb_InputDouble);
@@ -1304,6 +1305,7 @@ DXE_EXPORT_TABLE (libfb_symbol_table)
     DXE_EXPORT_ASM (_fb_ConsoleGetTopRow)
     DXE_EXPORT_ASM (_fb_OCTEx_b)
     DXE_EXPORT_ASM (_fb_SetDate)
+    DXE_EXPORT_ASM (___fb_dos_no_dpmi_yield)
     DXE_EXPORT_ASM (_fb_WstrHexEx_l)
     DXE_EXPORT_ASM (_fb_DatePart)
     DXE_EXPORT_ASM (_fb_InputDouble)

src/rtlib/dos/sys_delay.c

@@ -3,12 +3,62 @@
 	#include "../fb_private_thread.h"
 #endif
 #include <unistd.h>
+#include <time.h>
+#include <dpmi.h>
+
+
+/* __fb_dos_no_dpmi_yield
+ * - 0 (default), __dpmi_yield() is called in the busy loop for delays
+ * - non-zero, do not call __dpmi_yield() which seems will prevent
+ *   crashes under some dos extenders
+ *
+ * in fb:
+ *   extern "c"
+ *     extern as unsigned long __fb_dos_no_dpmi_yield
+ *   end extern
+ *   __fb_dos_no_dpmi_yield = 1
+ */
+
+extern unsigned int __fb_dos_no_dpmi_yield;
+unsigned int __fb_dos_no_dpmi_yield = 0;
+
+#if !defined(ENABLE_MT)
+
+/* usleep() copied from djgpp libc implementation */
+static unsigned int usleep_private(unsigned int _useconds)
+{
+	clock_t cl_time;
+	clock_t start_time = clock();
+
+	/* 977 * 1024 is about 1e6.  The funny logic keeps the math from
+	   overflowing for large _useconds */
+	_useconds >>= 10;
+	cl_time = _useconds * CLOCKS_PER_SEC / 977;
+
+	while (1)
+	{
+		clock_t elapsed = clock() - start_time;
+		if (elapsed >= cl_time)
+		{
+			break;
+		}
+	}
+	return 0;
+}
+#endif /* !defined(ENABLE_MT) */
 
 FBCALL void fb_Delay( int msecs )
 {
 #if defined ENABLE_MT
-        __pthread_usleep(msecs * 1000);
+	__pthread_usleep(msecs * 1000);
 #else
-        usleep(msecs * 1000);
+	if( __fb_dos_no_dpmi_yield )
+	{
+		usleep_private(msecs * 1000);
+	}
+	else
+	{
+		usleep(msecs * 1000);
+	}
 #endif
 }