This example works fine in Embedded v2.5 but fails in Embedded v3.0.
Test query: select * from RDB$COLLATIONS (you can use any other)
Sources of client application is attached. Compiled binaries are attached too (compiled with Delphi XE2 with IBX components).
How to reproduce in 2.5 - client application would not hang:
1) unzip the embedded server (http://sourceforge.net/projects/firebird/files/firebird-win32/2.5.6-Release/Firebird-188.8.131.52020-0_Win32_embed.zip/download
2) create empty database
3) move test application (MultiThreaded.exe) to the folder where embedded server is located
4) MultiThreaded.exe test_2_5.fdb sysdba masterkey
How to reproduce in 3.0 - client application would hang:
1) unzip Zip kit for manual/custom installs (https://sourceforge.net/projects/firebird/files/firebird-win32/3.0.1-Release/Firebird-184.108.40.206609-0_Win32.zip/download
2) copy the file fbclient.dll to gds32.dll (if IBX is used)
3) don't change the providers parameter on then config file (use default value #Providers = Remote,Engine12,Loopback)
4) create empty database
5) MultiThreaded.exe test_3_0.fdb sysdba masterkey
When was tested the Alfa release (in November of last year) - client application was not hang.