Comments on Simple inter application communication

[sinsi]

The sending thread is blocked until the receiving thread processes the message.

That's the problem,

Microsoft document the usage, usage is determined by the programmer.

In this case, by other programmers. According to spy++ there are around 300 top level windows going.

[aw27]

Microsoft document the usage, usage is determined by the programmer

In your caller.asm you have used PostMessage for buttons 2 to 8 either because you have seen something wrong with SendMessage or because you like to try multiple alternatives.
In the last case, why have you not tested SendNotifyMessage, SendMessageTimeout or SendMessageCallback as well?

[hutch--]

Nah, it was because the first 2 buttons were originally used to show or hide the slave window. It does not matter much in this context as both work.