...continued from "TCP stream socket send() thread safety" thread

Hello!

So, first the ending of the old story... I did not work with Windows for quite a long time already that's why assumption
 regarding necessity to read until WSAEWOULDBLOCK is returned was incorrect. For programmer's convenience Windows re-
enables socket select event signalling after any call to recv(). However, handle shuffling was still an issue.

Nevertheless, after corrections to client the problem is not gone.
I had to make further investigations. I ran Wireshark (formerly, Ethereal) on Windows machine to investigate the problem
.

Here is normal request-response for a heartbeat packet (172.25.31.241 is QNX host, 172.25.31.249 is Windows client):
======begin======
No.     Time        Source                Destination           Protocol Info
 115272 530.469917  172.25.31.249         172.25.31.241         TCP      2789 > 16015 [PSH, ACK] Seq=71129 Ack=4198257 
Win=64959 [TCP CHECKSUM INCORRECT] Len=16

Frame 115272 (70 bytes on wire, 70 bytes captured)
    Arrival Time: Dec 12, 2007 14:51:19.841042000
    [Time delta from previous captured frame: 0.130069000 seconds]
    [Time delta from previous displayed frame: 6.644444000 seconds]
    [Time since reference or first frame: 530.469917000 seconds]
    Frame Number: 115272
    Frame Length: 70 bytes
    Capture Length: 70 bytes
    [Frame is marked: False]
    [Protocols in frame: eth:ip:tcp:data]
    [Coloring Rule Name: Checksum Errors]
    [Coloring Rule String: cdp.checksum_bad==1 || edp.checksum_bad==1 || ip.checksum_bad==1 || tcp.checksum_bad==1 || 
udp.checksum_bad==1]
Ethernet II, Src: AsustekC_5c:57:23 (00:15:f2:5c:57:23), Dst: Intel_b9:5d:30 (00:0e:0c:b9:5d:30)
    Destination: Intel_b9:5d:30 (00:0e:0c:b9:5d:30)
        Address: Intel_b9:5d:30 (00:0e:0c:b9:5d:30)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
    Source: AsustekC_5c:57:23 (00:15:f2:5c:57:23)
        Address: AsustekC_5c:57:23 (00:15:f2:5c:57:23)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
    Type: IP (0x0800)
Internet Protocol, Src: 172.25.31.249 (172.25.31.249), Dst: 172.25.31.241 (172.25.31.241)
    Version: 4
    Header length: 20 bytes
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
        0000 00.. = Differentiated Services Codepoint: Default (0x00)
        .... ..0. = ECN-Capable Transport (ECT): 0
        .... ...0 = ECN-CE: 0
    Total Length: 56
    Identification: 0x139f (5023)
    Flags: 0x04 (Don't Fragment)
        0... = Reserved bit: Not set
        .1.. = Don't fragment: Set
        ..0. = More fragments: Not set
    Fragment offset: 0
    Time to live: 128
    Protocol: TCP (0x06)
    Header checksum: 0x4f04 [correct]
        [Good: True]
        [Bad : False]
    Source: 172.25.31.249 (172.25.31.249)
    Destination: 172.25.31.241 (172.25.31.241)
Transmission Control Protocol, Src Port: 2789 (2789), Dst Port: 16015 (16015), Seq: 71129, Ack: 4198257, Len: 16
    Source port: 2789 (2789)
    Destination port: 16015 (16015)
    Sequence number: 71129    (relative sequence number)
    [Next sequence number: 71145    (relative sequence number)]
    Acknowledgement number: 4198257    (relative ack number)
    Header length: 20 bytes
    Flags: 0x18 (PSH, ACK)
        0... .... = Congestion Window Reduced (CWR): Not set
        .0.. .... = ECN-Echo: Not set
        ..0. .... = Urgent: Not set
        ...1 .... = Acknowledgment: Set
        .... 1... = Push: Set
        .... .0.. = Reset: Not set
        .... ..0. = Syn: Not set
        .... ...0 = Fin: Not set
    Window size: 64959
    Checksum: 0x9847 [incorrect, should be 0xe476 (maybe caused by "TCP checksum offload"?)]
     ...