This section shows three example programs using gipc. These examples have been created mainly for educational purposes and might therefore lack real-world purpose :-). I hope they are useful!

The latest version of these examples can be found on GitHub (that code there is also run as part of CI and contains a few consolidations for platforms like Windows and mac OS which are left out in the snippets below).

Example 1: gipc.pipe()-based messaging from greenlet in parent to child

Pretty basic gevent and gipc concepts are explained by means of the following messaging example:

import gevent
import gipc

def main():
    with gipc.pipe() as (r, w):
        p = gipc.start_process(target=child_process, args=(r, ))
        wg = gevent.spawn(writegreenlet, w)
        except KeyboardInterrupt:

def writegreenlet(writer):
    while True:
        writer.put("written to pipe from a greenlet running in the main process")

def child_process(reader):
    while True:
        print "Child process got message from pipe:\n\t'%s'" % reader.get()

if __name__ == "__main__":

The context manager with gipc.pipe() as (r, w) creates a pipe with read handle r and write handle w. On context exit (latest) the pipe ends will be closed properly.

After creating the pipe context, the above code spawns a child process via gipc.start_process(). The child process is instructed to execute the target function named child_process whereas the pipe read handle r is provided as an argument to this target function. Within child_process() an endless loop waits for objects on the read end of the pipe via the cooperatively blocking call to reader.get(). Upon retrieval, it immediately writes their string representation to stdout.

After invocation of the child process (represented by an object bound to name p), a greenlet wg is spawned within the main process. This greenlet executes the function writegreenlet, whereas the pipe write handle w is provided as an argument. Within this greenlet, one string per second is written to the write end of the pipe.

After spawning wg, p.join() is called immediately in the parent process. p.join() is blocking cooperatively, i.e. it allows for a context switch into the write greenlet (this actually is the magic behind gevent/greenlets). Hence, the write greenlet is ‘running’ while p.join() cooperatively waits for the child process to terminate. The write greenlet spends most of its time in gevent.sleep(), which is also blocking cooperatively, allowing for context switches back to the main greenlet in the parent process, which is executing p.join(). In this state, one message per second is passed between parent and child until a KeyboardInterrupt exception is raised in the parent.

Upon KeyboardInterrupt, the parent first kills the write greenlet and blocks cooperatively until it has stopped. Then it terminates the child process (via SIGTER on Unix) and waits for it to exit via p.join().

Example 2: serving multiple clients (in child) from one server (in parent)

For pure API and reliability demonstration purposes, this example implements TCP communication between a server in the parent process and multiple clients in one child process:

  1. gevent’s StreamServer is started in a greenlet within the initial (parent) process. For each connecting client, it receives one newline-terminated message and echoes it back.
  2. A child process is started using gipc. Its starting point is the function clientprocess. There, N TCP clients are started concurrently from N greenlets.
  3. Each client sends one message, validates the echo response and terminates.
  4. The child process terminates.
  5. After the child process is joined in the parent, the server is killed.
  6. The server greenlet is joined.
import gevent
from gevent.server import StreamServer
from gevent import socket
import gipc
import time

PORT = 1337
N_CLIENTS = 1000

def serve(sock, addr):
    f = sock.makefile()

def server():
    ss = StreamServer(('localhost', PORT), serve).serve_forever()

def clientprocess():
    t1 = time.time()
    clients = [gevent.spawn(client) for _ in xrange(N_CLIENTS)]
    duration = time.time()-t1
    print "%s clients served within %.2f s." % (N_CLIENTS, duration)

def client():
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.connect(('localhost', PORT))
    f = sock.makefile()
    assert f.readline() == MSG

if __name__ == "__main__":
    s = gevent.spawn(server)
    c = gipc.start_process(clientprocess)

Output on my test machine: 1000 clients served within 0.54 s.

Example 3: time-synchronization between processes

Child process creation may take a significant amount of time, especially on Windows. The exact amount of time is not predictable.

When code in the parent should only proceed in the moment the code in the child has reached a certain state, the proper way to tackle this is a bidirectional synchronization handshake:

  • Process A sends a synchronization request to process B and waits for an acknowledgment response. It proceeds upon retrieval.
  • Process B sends the acknowledgment in the moment it retrieves the sync request and proceeds.

This concept can easily be implemented using a bidirectional gipc.pipe():

import gevent
import gipc
import time

def main():
    with gipc.pipe(duplex=True) as (cend, pend):
        # `cend` is the channel end for the child, `pend` for the parent.
        p = gipc.start_process(writer_process, args=(cend,))
        # Synchronize with child process.
        assert pend.get() == "ACK"
        # Now in sync with child.
        ptime = time.time()
        ctime = pend.get()
        print "Time delta: %.8f s." % abs(ptime - ctime)

def writer_process(cend):
    with cend:
        assert cend.get() == "SYN"
        # Now in sync with parent.

if __name__ == "__main__":

The marked code blocks in parent and child are entered quasi-simultaneously. Example output on my test machine (Linux): Time delta: 0.00005388 s. On Windows, time.time()’s precision is not sufficient to resolve the time delta (and time.clock() is not applicable for comparing times across processes).