P = subprocess.Popen()īelow script is addon version of the above script. It capture output and error of the called script. It also wait for launched process to finish. P = subprocess.Popen(, stdout=subprocess.PIPE, stderr=subprocess.PIPE) Finally it displays the output and error code. #Python subprocess run in background how to.logMessage ( 'Started task " ' 56 'iterations)'. 25 Raising exceptions will crash QGIS, so we handle them 26 internally and raise them in self.finished 27 """ 28 QgsMessageLog.
24 This method MUST return True or False. 22 Should periodically test for isCanceled() to gracefully 23 abort. exception = None 19 20 def run ( self ): 21 """Here you implement your heavy lifting. Several instances of RandomIntegerSumTask (with subtasks) are generatedĪnd added to the task manager, demonstrating two types ofġ import random 2 from time import sleep 3 4 from re import ( 5 QgsApplication, QgsTask, QgsMessageLog, Qgis 6 ) 7 8 MESSAGE_CATEGORY = 'RandomIntegerSumTask' 9 10 class RandomIntegerSumTask ( QgsTask ): 11 """This shows how to subclass QgsTask""" 12 13 def _init_ ( self, description, duration ): 14 super (). If the random number is 42, the task is aborted and an exception is Generate 100 random integers between 0 and 500 during a specified period In this example RandomIntegerSumTask extends QgsTask and will The status of tasks can be monitored using QgsTask and The scheduling of the tasks is influenced by the task priority, which That task to the manager, and the manager will cleanup and delete The addTask() function of the task manager.Īdding a task to the manager automatically transfers ownership of Once the task has been created it can be scheduled for running using If a layer on which a task depends is not available, the task will be If a task depends on a layer being available, this can be stated If a task on which another task depends is canceled, the dependentĬircular dependencies can make deadlocks possible, so be careful. Wherever possible dependencies will be executed in parallel in order When a dependency is stated, the task manager will automaticallyĭetermine how these dependencies will be executed. Qt widgets must only be accessed or modified from the main thread.ĭata that is used in a task must be copied before the task is started.Īttempting to use them from background threads will result inĭependencies between tasks can be described using the addSubTask() Like creating new widgets or interacting with existing widgets. QgsVectorLayer, QgsProject or perform any GUI based operations
Use any QObject that lives on the main thread, such as accessing Task from a processing algorithmĪny background task (regardless of how it is created) must NEVER Tasks - doing heavy work in the background Expressions, Filtering and Calculating Values QGIS Desktop User Guide/Manual (QGIS 3.28).
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