From aeeb4acdc8695a640021dbc6902ab3279652583d Mon Sep 17 00:00:00 2001
From: Bill Erickson <berick@esilibrary.com>
Date: Tue, 14 Feb 2012 09:10:58 -0500
Subject: [PATCH] Perl parent/child write improvements

* Updated variable names for clarity
* Added more inline comments
* Added additional error logging
* For severe read errors, allow the child to gracefully skip the request

Signed-off-by: Bill Erickson <berick@esilibrary.com>
Signed-off-by: Jason Stephenson <jstephenson@mvlc.org>
Signed-off-by: Mike Rylander <mrylander@gmail.com>
---
 src/perl/lib/OpenSRF/Server.pm | 44 ++++++++++++++++++++++++------------------
 1 file changed, 25 insertions(+), 19 deletions(-)

diff --git a/src/perl/lib/OpenSRF/Server.pm b/src/perl/lib/OpenSRF/Server.pm
index 32954f2..6cab1dd 100644
--- a/src/perl/lib/OpenSRF/Server.pm
+++ b/src/perl/lib/OpenSRF/Server.pm
@@ -587,13 +587,13 @@ sub run {
 sub wait_for_request {
     my $self = shift;
 
-    my $data = '';
-    my $buf_size = 4096;
-    my $nonblock = 0;
+    my $data = ''; # final request data
+    my $buf_size = 4096; # default linux pipe_buf (atomic window, not total size)
     my $read_pipe = $self->{pipe_to_parent};
-    my $data_size;
-    my $total_read;
-    my $first_read = 1;
+    my $bytes_needed; # size of the data we are about to receive
+    my $bytes_recvd; # number of bytes read so far
+    my $first_read = 1; # true for first loop iteration
+    my $read_error;
 
     while (1) {
 
@@ -611,39 +611,45 @@ sub wait_for_request {
         $self->set_nonblock($read_pipe);
 
         while (1) {
-            # pull as much data from the pipe as possible
+            # read all of the available data
 
             my $buf = '';
-            my $bytes_read = sysread($self->{pipe_to_parent}, $buf, $buf_size);
-
-            unless(defined $bytes_read) {
-                $logger->error("server: error reading data pipe: $!") unless EAGAIN == $!;
+            my $nbytes = sysread($self->{pipe_to_parent}, $buf, $buf_size);
+
+            unless(defined $nbytes) {
+                if ($! != EAGAIN) {
+                    $logger->error("server: error reading data from parent: $!.  ".
+                        "bytes_needed=$bytes_needed; bytes_recvd=$bytes_recvd; data=$data");
+                    $read_error = 1;
+                }
                 last;
             }
 
-            last if $bytes_read <= 0; # no more data available for reading
+            last if $nbytes <= 0; # no more data available for reading
 
-            $total_read += $bytes_read;
+            $bytes_recvd += $nbytes;
             $data .= $buf;
         }
 
-        # we've read all the data currently available on the pipe.
-        # let's see if we're done.
+        $self->set_block($self->{pipe_to_parent});
+        return undef if $read_error;
 
+        # extract the data size and remove the header from the final data
         if ($first_read) {
-            # extract the data size and remove the size header
             my $wps_size = OpenSRF::Server::WRITE_PIPE_DATA_SIZE;
-            $data_size = int(substr($data, 0, $wps_size)) + $wps_size;
+            $bytes_needed = int(substr($data, 0, $wps_size)) + $wps_size;
             $data = substr($data, $wps_size);
             $first_read = 0;
         }
 
-        $self->set_block($self->{pipe_to_parent});
 
-        if ($total_read == $data_size) {
+        if ($bytes_recvd == $bytes_needed) {
             # we've read all the data. Nothing left to do
             last;
         }
+
+        $logger->info("server: child process read all available pipe data.  ".
+            "waiting for more data from parent.  bytes_needed=$bytes_needed; bytes_recvd=$bytes_recvd");
     }
 
     return $data;
-- 
2.11.0