under_pressure

A program showing how to utilize the Pony backpressure system.

How to Compile

With a minimal Pony installation, in the same directory as this README file run ponyc. You should see content building the necessary packages, which ends with:

...
Generating
 Reachability
 Selector painting
 Data prototypes
 Data types
 Function prototypes
 Functions
 Descriptors
Optimising
Writing ./under_pressure.o
Linking ./under_pressure

How to Run

Once under_pressure has been compiled, in the same directory as this README file run ./under_pressure. You should see a message reporting a connection failure.

$ ./under_pressure
connect_failed

This failure is because there is no receiver for the data under_pressue is receiving. You can start one with netcat.

# Data receiver
nc -l 127.0.0.1 7669 >> /dev/null

Now run under_pressure (your output w)

$ ./under_pressure
Querying and setting socket options:
        getsockopt so_error = 0
        getsockopt get_tcp_nodelay = 0
        getsockopt set_tcp_nodelay(true) return value = 13
        getsockopt get_tcp_nodelay = 0
        getsockopt rcvbuf = 131072
        getsockopt sndbuf = 2626560
        setsockopt rcvbuf 5000 return was 0
        setsockopt sndbuf 5000 return was 0

If you then stop the netcat process you will see under_pressure respond that is it experiencing backpressure. Restart netcat and under_pressure will release backpressure. If you look at a system monitor while under backpressure you will notice under_pressure has very low usage -- no actors are running!

Program Modifications

Modify the program to use more than one TCPConnection -- all actors will respond to backpressure on its own.