kernel: add #define to disable subprocess code

This helps debug whether the Julia replacements for GAP's subprocess
code are fully in place, and ensure we don't forget anything. More
importantly, it disables the SIGCHLD handler in the GAP kernel.

In the future we could also add configure flag to set it.

src/iostream.c

@@ -37,6 +37,8 @@
 
 #include "config.h"
 
+#ifndef GAP_DISABLE_SUBPROCESS_CODE
+
 #include <errno.h>
 #include <fcntl.h>
 #include <signal.h>
@@ -804,6 +806,60 @@ static Obj FuncFD_OF_IOSTREAM(Obj self, Obj stream)
     return result;
 }
 
+#else // !defined(GAP_DISABLE_SUBPROCESS_CODE)
+
+int CheckChildStatusChanged(int childPID, int status)
+{
+    return 0;
+}
+
+static Obj FuncCREATE_PTY_IOSTREAM(Obj self, Obj dir, Obj prog, Obj args)
+{
+    return Fail;
+}
+
+static Obj FuncWRITE_IOSTREAM(Obj self, Obj stream, Obj string, Obj len)
+{
+    return Fail;
+}
+
+static Obj FuncREAD_IOSTREAM(Obj self, Obj stream, Obj len)
+{
+    return Fail;
+}
+
+static Obj FuncREAD_IOSTREAM_NOWAIT(Obj self, Obj stream, Obj len)
+{
+    return Fail;
+}
+
+static Obj FuncKILL_CHILD_IOSTREAM(Obj self, Obj stream)
+{
+    return 0;
+}
+
+static Obj FuncSIGNAL_CHILD_IOSTREAM(Obj self, Obj stream, Obj sig)
+{
+    return 0;
+}
+
+static Obj FuncCLOSE_PTY_IOSTREAM(Obj self, Obj stream)
+{
+    return 0;
+}
+
+static Obj FuncIS_BLOCKED_IOSTREAM(Obj self, Obj stream)
+{
+    return Fail;
+}
+
+static Obj FuncFD_OF_IOSTREAM(Obj self, Obj stream)
+{
+    return Fail;
+}
+
+#endif
+
 
 /****************************************************************************
 **
@@ -841,6 +897,7 @@ static StructGVarFunc GVarFuncs[] = {
 */
 static Int InitKernel(StructInitInfo * module)
 {
+#ifndef GAP_DISABLE_SUBPROCESS_CODE
     UInt i;
     PtyIOStreams[0].childPID = -1;
     for (i = 1; i < MAX_PTYS; i++) {
@@ -849,14 +906,16 @@ static Int InitKernel(StructInitInfo * module)
     }
     FreePtyIOStreams = MAX_PTYS - 1;
 
-    /* init filters and functions                                          */
-    InitHdlrFuncsFromTable(GVarFuncs);
-
 #if !defined(HPCGAP)
     /* Set up the trap to detect future dying children */
     signal(SIGCHLD, ChildStatusChanged);
 #endif
 
+#endif
+
+    /* init filters and functions                                          */
+    InitHdlrFuncsFromTable(GVarFuncs);
+
     return 0;
 }
 

src/sysfiles.c

@@ -2791,6 +2791,20 @@ void SySetErrorNo ( void )
 *F * * * * * * * * * * * * * file and execution * * * * * * * * * * * * * * *
 */
 
+#ifdef GAP_DISABLE_SUBPROCESS_CODE
+
+UInt SyExecuteProcess (
+    Char *                  dir,
+    Char *                  prg,
+    Int                     in,
+    Int                     out,
+    Char *                  args[] )
+{
+    return 255;
+}
+
+#else
+
 /****************************************************************************
 **
 *F  SyExecuteProcess( <dir>, <prg>, <in>, <out>, <args> ) . . . . new process
@@ -3027,6 +3041,7 @@ UInt SyExecuteProcess (
 
 #endif
 
+#endif // !GAP_DISABLE_SUBPROCESS_CODE
 
 /****************************************************************************
 **