Multiple subscribers to the same topic do not receive the same msgs

[gavanderhoorn]

Setup:

• compile the samples
• run a roscore
• start a single instance of talker
• start two instances of rostopic echo /chatter (rt0 and rt1 in the description below)

Observed:

both rt0 and rt1 start receiving messages, but rt0 gets the even publications, and rt1 gets the uneven publications (this is just an example, it could be the other way around):

output of rt0:

...

---
data: hello world 120

---
data: hello world 122

---
data: hello world 124
...

output of rt1:

...

---
data: hello world 121

---
data: hello world 123

---
data: hello world 125
...

Expected:

It would appear that the callback is called twice: once for each subscriber, giving each subscriber their own copy (or: a new message).

I would've expected the callback to be called once, and the resulting message (ie: hello world 121) copied to all connected subscribers.