1 files changed, 116 insertions, 0 deletions
diff --git a/training/dpmert/line_mediator.pl b/training/dpmert/line_mediator.pl
new file mode 100755
index 00000000..bc2bb24c
--- /dev/null
+++ b/training/dpmert/line_mediator.pl
@@ -0,0 +1,116 @@
+#!/usr/bin/perl -w
+#hooks up two processes, 2nd of which has one line of output per line of input, expected by the first, which starts off the communication
+
+# if you don't know how to fork/exec in a C program, this could be helpful under limited cirmustances (would be ok to liaise with sentserver)
+
+#WARNING: because it waits for the result from command 2 after sending every line, and especially if command 1 does the same, using sentserver as command 2 won't actually buy you any real parallelism.
+
+use strict;
+use IPC::Open2;
+use POSIX qw(pipe dup2 STDIN_FILENO STDOUT_FILENO);
+
+my $quiet=!$ENV{DEBUG};
+$quiet=1 if $ENV{QUIET};
+sub info {
+    local $,=' ';
+    print STDERR @_ unless $quiet;
+}
+
+my $mode='CROSS';
+my $ser='DIRECT';
+$mode='PIPE' if $ENV{PIPE};
+$mode='SNAKE' if $ENV{SNAKE};
+$mode='CROSS' if $ENV{CROSS};
+$ser='SERIAL' if $ENV{SERIAL};
+$ser='DIRECT' if $ENV{DIRECT};
+$ser='SERIAL' if $mode eq 'SNAKE';
+info("mode: $mode\n");
+info("connection: $ser\n");
+
+
+my @c1;
+if (scalar @ARGV) {
+    do {
+        push @c1,shift
+    } while scalar @ARGV && $c1[$#c1] ne '--';
+}
+pop @c1;
+my @c2=@ARGV;
+@ARGV=();
+(scalar @c1 && scalar @c2) || die qq{
+usage: $0 cmd1 args -- cmd2 args
+all options are environment variables.
+DEBUG=1 env var enables debugging output.
+CROSS=1 hooks up two processes, 2nd of which has one line of output per line of input, expected by the first, which starts off the communication.  crosses stdin/stderr of cmd1 and cmd2 line by line (both must flush on newline and output.  cmd1 initiates the conversation (sends the first line).    default: attempts to cross stdin/stdout of c1 and c2 directly (via two unidirectional posix pipes created before fork).
+SERIAL=1: (no parallelism possible) but lines exchanged are logged if DEBUG.
+if SNAKE then stdin -> c1 -> c2 -> c1 -> stdout.
+if PIPE then stdin -> c1 -> c2 -> stdout (same as shell c1|c2, but with SERIAL you can see the intermediate in real time; you could do similar with c1 | tee /dev/fd/2 |c2.
+DIRECT=1 (default) will override SERIAL=1.
+CROSS=1 (default) will override SNAKE or PIPE.
+};
+
+info("1 cmd:",@c1,"\n");
+info("2 cmd:",@c2,"\n");
+
+sub lineto {
+    select $_[0];
+    $|=1;
+    shift;
+    print @_;
+}
+
+if ($ser eq 'SERIAL') {
+    my ($R1,$W1,$R2,$W2);
+    my $c1p=open2($R1,$W1,@c1); # Open2 R W backward from Open3.
+    my $c2p=open2($R2,$W2,@c2);
+    if ($mode eq 'CROSS') {
+        while(<$R1>) {
+            info("1:",$_);
+            lineto($W2,$_);
+            last unless defined ($_=<$R2>);
+            info("1|2:",$_);
+            lineto($W1,$_);
+        }
+    } else {
+        my $snake=$mode eq 'SNAKE';
+        while(<STDIN>) {
+            info("IN:",$_);
+            lineto($W1,$_);
+            last unless defined ($_=<$R1>);
+            info("IN|1:",$_);
+            lineto($W2,$_);
+            last unless defined ($_=<$R2>);
+            info("IN|1|2:",$_);
+            if ($snake) {
+                lineto($W1,$_);
+                last unless defined ($_=<$R1>);
+                info("IN|1|2|1:",$_);
+            }
+            lineto(*STDOUT,$_);
+        }
+    }
+} else {
+    info("DIRECT mode\n");
+    my @rw1=POSIX::pipe();
+    my @rw2=POSIX::pipe();
+    my $pid=undef;
+    $SIG{CHLD} = sub { wait };
+    while (not defined ($pid=fork())) {
+        sleep 1;
+    }
+    my $pipe = $mode eq 'PIPE';
+    unless ($pipe) {
+        POSIX::close(STDOUT_FILENO);
+        POSIX::close(STDIN_FILENO);
+    }
+    if ($pid) {
+        POSIX::dup2($rw1[1],STDOUT_FILENO);
+        POSIX::dup2($rw2[0],STDIN_FILENO) unless $pipe;
+        exec @c1;
+    } else {
+        POSIX::dup2($rw2[1],STDOUT_FILENO) unless $pipe;
+        POSIX::dup2($rw1[0],STDIN_FILENO);
+        exec @c2;
+    }
+    while (wait()!=-1) {}
+}