Bug report #20878

Updated by Jürgen Fischer over 1 year ago

I tried to make some tasks in parallel with qgis.

There is the test script

<pre>
import
@import concurrent.futures
import time, random # add some random sleep time

offset = 2 # you don't supply these so
output1 = list()
output2 = list()
output3 = list()
start = time.time() # let's see how long this takes

# we can swap out ProcessPoolExecutor for ThreadPoolExecutor
with concurrent.futures.ProcessPoolExecutor() as executor:
for out1, out2, out3 in executor.map(procedure, range(0, 10)):
# put results into correct output list
output1.append(out1)
output2.append(out2)
output3.append(out3)
finish = time.time()
# these kinds of format strings are only available on Python 3.6:
# time to upgrade!
print(f'original inputs: {repr(output1)}')
print(f'total time to execute {sum(output2)} = sum({repr(output2)})')
print(f'time saved by parallelizing: {sum(output2) - (finish-start)}')
print(f'returned in order given: {repr(output3)}')

def calc_stuff(parameter=None): # these are examples.
sleep_time = random.choice([0, 1, 2, 3, 4, 5])
time.sleep(sleep_time)
return parameter / 2, sleep_time, parameter * parameter

def procedure(j): # just factoring out the
parameter = j * offset # procedure
# call the calculation
return calc_stuff(parameter=parameter)
</pre>

calc_stuff(parameter=parameter)@

This script doesn't behave as expected. Instead it launches 3 additional QGIS instances.

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