multithreading

问题 I was reading the Intel instruction set guide 64-ia-32 guide to get an idea on memory fences. My question is that for an example with SFENCE, in order to make sure that all store operations are globally visible, does the multi-core CPU parks all the threads even running on other cores till the cache coherence achieved ? 回答1: Barriers don't make other threads/cores wait. They make some operations in the current thread wait , depending on what kind of barrier it is. Out-of-order execution of

问题 I was reading the Intel instruction set guide 64-ia-32 guide to get an idea on memory fences. My question is that for an example with SFENCE, in order to make sure that all store operations are globally visible, does the multi-core CPU parks all the threads even running on other cores till the cache coherence achieved ? 回答1: Barriers don't make other threads/cores wait. They make some operations in the current thread wait , depending on what kind of barrier it is. Out-of-order execution of

问题 I was reading the Intel instruction set guide 64-ia-32 guide to get an idea on memory fences. My question is that for an example with SFENCE, in order to make sure that all store operations are globally visible, does the multi-core CPU parks all the threads even running on other cores till the cache coherence achieved ? 回答1: Barriers don't make other threads/cores wait. They make some operations in the current thread wait , depending on what kind of barrier it is. Out-of-order execution of

问题 I was reading the Intel instruction set guide 64-ia-32 guide to get an idea on memory fences. My question is that for an example with SFENCE, in order to make sure that all store operations are globally visible, does the multi-core CPU parks all the threads even running on other cores till the cache coherence achieved ? 回答1: Barriers don't make other threads/cores wait. They make some operations in the current thread wait , depending on what kind of barrier it is. Out-of-order execution of

问题 I'm using ThreadPoolExecutor to speed up data processing. The problem is that the thread pool creates new database connections and Django doesn't close them. I do have CONN_MAX_AGE in settings.py and I already tried to call django.db.close_old_connections() . Here is a code example: def compute(job): result = FooModel.objects.filter(...).aggregate(...) return BarModel.objects.create(result) def process(dataset): thread_pool = ThreadPoolExecutor(max_workers=20) futures = [] for job in dataset:

问题 I tried to use AddOrUpdate method in ConcurrentDictionary. From the "Remarks" section on this page https://msdn.microsoft.com/en-us/library/dd287191(v=vs.110).aspx. it says "However, delegates for these methods are called outside the locks to avoid the problems that can arise from executing unknown code under a lock. Therefore, the code executed by these delegates is not subject to the atomicity of the operation." So I am not sure whether it is thread safe. I have one case, if the key is not

问题 I tried to use AddOrUpdate method in ConcurrentDictionary. From the "Remarks" section on this page https://msdn.microsoft.com/en-us/library/dd287191(v=vs.110).aspx. it says "However, delegates for these methods are called outside the locks to avoid the problems that can arise from executing unknown code under a lock. Therefore, the code executed by these delegates is not subject to the atomicity of the operation." So I am not sure whether it is thread safe. I have one case, if the key is not

问题 I tried to use AddOrUpdate method in ConcurrentDictionary. From the "Remarks" section on this page https://msdn.microsoft.com/en-us/library/dd287191(v=vs.110).aspx. it says "However, delegates for these methods are called outside the locks to avoid the problems that can arise from executing unknown code under a lock. Therefore, the code executed by these delegates is not subject to the atomicity of the operation." So I am not sure whether it is thread safe. I have one case, if the key is not

问题 On API level 28(Pie) a new method is introduced in the Context class to get Executor for the main thread getMainExecutor(). How to get this executor on API level below 28? 回答1: You can use (in activity for example): ContextCompat.getMainExecutor(this); https://developer.android.com/reference/androidx/core/content/ContextCompat.html#getMainExecutor(android.content.Context) 回答2: You can use code snippet from retrofit https://github.com/square/retrofit/blob/master/retrofit/src/main/java

问题 The Java memory model guarantees a happens-before relationship between an object's construction and finalizer: There is a happens-before edge from the end of a constructor of an object to the start of a finalizer (§12.6) for that object. As well as the constructor and the initialization of final fields: An object is considered to be completely initialized when its constructor finishes. A thread that can only see a reference to an object after that object has been completely initialized is