1 files changed, 99 insertions, 0 deletions
diff --git a/user/progR.c b/user/progR.c
new file mode 100644
index 0000000..1d47f6b
--- /dev/null
+++ b/user/progR.c
@@ -0,0 +1,99 @@
+#include <common.h>
+
+/**
+** User function R:   exit, sleep, write, fork, getpid, getppid,
+**
+** Reports itself and its sequence number, along with its PID and
+** its parent's PID. It then delays, forks, delays, reports again,
+** and exits.
+**
+** Invoked as:  userR  x  n  [ s ]
+**	 where x is the ID character
+**		   n is the sequence number of the initial incarnation
+**		   s is the initial delay time (defaults to 10)
+*/
+
+USERMAIN( main ) {
+	char ch = 'r';	// default character to print
+	int delay = 10;	// initial delay count
+	int seq = 99;	// my sequence number
+	char buf[128];
+
+	// process the command-line arguments
+	switch( argc ) {
+	case 4:	delay = str2int( argv[3], 10 );
+			// FALL THROUGH
+	case 3:	seq = str2int( argv[2], 10 );
+			// FALL THROUGH
+	case 2:	ch = argv[1][0];
+			break;
+	default:
+			sprint( buf, "userR: argc %d, args: ", argc );
+			cwrites( buf );
+			for( int i = 0; i <= argc; ++i ) {
+				sprint( buf, " %s", argv[argc] ? argv[argc] : "(null)" );
+				cwrites( buf );
+			}
+			cwrites( "\n" );
+	}
+
+	/*
+	** C oddity: a label cannot immediately precede a declaration.
+	**
+	** Declarations are not considered "statements" in C. Prior to
+	** C99, all declarations had to precede any statements inside a
+	** block. Labels can only appear before statements.  C99 allowed
+	** the mixing of declarations and statements, but did not relax
+	** the requirement that labels precede only statements.
+	**
+	** That's why the declarations of these variables occur before the
+	** label, but their initializations occur after the label.
+	**
+	** As the PSA says on TV, "The more you know..." :-)
+	*/
+
+	int32_t pid;
+	int32_t ppid;
+
+ restart:
+
+	// announce our presence
+	pid = getpid();
+	ppid = getppid();
+
+	sprint( buf, " %c[%d,%d,%d]", ch, seq, pid, ppid );
+	swrites( buf );
+
+	sleep( SEC_TO_MS(delay) );
+
+	// create the next child in sequence
+	if( seq < 5 ) {
+		++seq;
+		int32_t n = fork();
+		switch( n ) {
+		case -1:
+			// failure?
+			sprint( buf, "** R[%d] fork code %d\n", pid, n );
+			cwrites( buf );
+			break;
+		case 0:
+			// child
+			goto restart;
+		default:
+			// parent
+			--seq;
+			sleep( SEC_TO_MS(delay) );
+		}
+	}
+
+	// final report - PPID may change, but PID and seq shouldn't
+	pid = getpid();
+	ppid = getppid();
+	sprint( buf, " %c[%d,%d,%d]", ch, seq, pid, ppid );
+	swrites( buf );
+
+	exit( 0 );
+
+	return( 42 );  // shut the compiler up!
+
+}