Using Python 2.7 on Windows, and will use Jython which support true multi-threading. The method sendMessage is used to receive message from a specific client, and the client may send the same message to a few other clients (which is what parameter receivers is for, and receivers is a list). The method receiveMessage is used to receive message for a specific client, which are sent from other clients.
The question is whether I need any locks for method sendMessage and receiveMessage? I think there is no need, since even if a client X is receiving its message, it is perfect fine for another client Y to append to message pool to deliver message to client X. And I think for defaultdict/list, append/pop are both atomic and no need for protection.
Please feel free to correct me if I am wrong.
from collections import defaultdict
class Foo:
def __init__(self):
# key: receiver client ID, value: message
self.messagePool = defaultdict(list)
def sendMessage(self, receivers, message):
# check valid for receivers
for r in receivers:
self.messagePool[r].append(message)
def receiveMessage(self, clientID):
result = []
while len(self.messagePool[clientID]) > 0:
result.append(self.messagePool[clientID].pop(0))
return result
I think this question is already well-answered for CPython here and here (basically, you're safe because of GIL, although nothing in documentation (like on defaultdict or list) officially says about that). But I understand your concern about Jython, so let's solve it using some official source, like Jython source code. A pythonic list is a javaish PyList there with this kind of code:
public void append(PyObject o) {
list_append(o);
}
final synchronized void list_append(PyObject o) {
...
}
public PyObject pop(int n) {
return list_pop(n);
}
final synchronized PyObject list_pop(int n) {
...
}
And as we have these methods synchronized, we can be sure that list appends and pops are also thread-safe with Jython. Thus, your code seems to be safe wrt threading.
Although Queue suggestion is still valid one, it really is more appropriate for this use case.