You can learn more about MessageQueues here and here. Just like Javascript, Cocoa in iOS, to avoid cocurrency access racing, many App related framework adapts a single thread model. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. What's message queue in Android? Ask Question. Asked 3 years, 7 months ago. Active 19 days ago. Viewed 2k times. I am asking because I was reading about the method post of the class View. Thank you in advance.
Improve this question. Add a comment. Active Oldest Votes. When would you use this method? Improve this answer. To check and update to the latest version of the Play Store, swipe through the app drawer or home screen to locate the app. Open the Play Store and swipe to the right. A slide-out menu will appear. Select the Play Store version. Your device running out of space could also be the reason why an app remains on the download queue for Android. You can check how much room is left on your device and which applications are consuming the most memory.
You can also delete long text conversations and files like audio books. Once you have cleared enough space, check if the queued app has started downloading. Sadly, the software running on our devices do not always work at optimal levels. This could also lead to pending downloads. Restarting your device is one way to go around this problem.
You can also try resetting the settings on your device if the problem continues even after you rebooted your phone or tablet. Bugs or other issues with the Play Store or your Google ID can also cause apps to freeze when being downloaded. Logging out and signing back in to the Play Store can fix this problem. Start by going to Settings.
To log back in, simply open the Play Store. You just have to understand that there are several reasons why this happens and take comfort in the fact that there are numerous ways to go about this. How many times have you experienced problems with downloads Android phone? However, for cases where data must be transferred between processes with less overhead and no kernel involvement, the Fast Message Queue FMQ system is used. FMQ creates message queues with the desired properties. Both queue types are not allowed to underflow read from an empty queue will fail and can only have one writer.
An unsynchronized queue has only one writer, but can have any number of readers. There is one write position for the queue; however, each reader keeps track of its own independent read position. Writes to the queue always succeed are not checked for overflow as long as they are no larger than the configured queue capacity writes larger than the queue capacity fail immediately.
As each reader may have a different read position, rather than waiting for every reader to read every piece of data, data is allowed to fall off the queue whenever new writes need the space. Reads are responsible for retrieving data before it falls off the end of the queue. A read that attempts to read more data than is available either fails immediately if nonblocking or waits for enough data to be available if blocking.
A read that attempts to read more data than the queue capacity always fails immediately. If a reader fails to keep up with the writer, so that the amount of data written and not yet read by that reader is larger than the queue capacity, the next read does not return data; instead, it resets the reader's read position to equal the latest write position then returns failure.
If the data available to read is checked after overflow but before the next read, it shows more data available to read than the queue capacity, indicating overflow has occurred. If the queue overflows between checking available data and attempting to read that data, the only indication of overflow is that the read fails. A synchronized queue has one writer and one reader with a single write position and a single read position. It is impossible to write more data than the queue has space for or read more data than the queue currently holds.
Depending on whether the blocking or nonblocking write or read function is called, attempts to exceed available space or data either return failure immediately or block until the desired operation can be completed. Attempts to read or write more data than the queue capacity will always fail immediately. A message queue requires multiple MessageQueue objects: one to be written to, and one or more to be read from. There is no explicit configuration of which object is used for writing or reading; it is up to the user to ensure that no object is used for both reading and writing, that there is at most one writer, and, for synchronized queues, that there is at most one reader.
The second side of the message queue is created using an MQDescriptor object obtained from the first side. The MQDescriptor contains information about the queue, including:. The resetPointers parameter indicates whether to reset the read and write positions to 0 while creating this MessageQueue object.
In an unsynchronized queue, the read position which is local to each MessageQueue object in unsynchronized queues is always set to 0 during creation.
Typically, the MQDescriptor is initialized during creation of the first message queue object. For the long form, the EventFlag can be supplied explicitly in each readBlocking and writeBlocking call.
One of the queues may be initialized with an internal event flag, which must then be extracted from that queue's MessageQueue objects using getEventFlagWord and used to create EventFlag objects in each process for use with other FMQs. Alternatively, the EventFlag objects can be initialized with any suitable shared memory.
In general, each queue should use only one of non-blocking, short-form blocking, or long-form blocking. It is not an error to mix them, but careful programming is required to get the desired result.
In an unsynchronized queue:. These methods do not block; they either succeed and return true , or return failure false immediately. The readBlocking and writeBlocking methods wait until the requested operation can be completed, or until they timeout a timeOutNanos value of 0 means never timeout. Blocking operations are implemented using an event flag word.
By default, each queue creates and uses its own flag word to support the short form of readBlocking and writeBlocking. It is possible for multiple queues to share a single word, so that a process can wait on writes or reads to any of the queues. A pointer to a queue's event flag word can be obtained by calling getEventFlagWord , and that pointer or any pointer to a suitable shared memory location can be used to create an EventFlag object to pass into the long form of readBlocking and writeBlocking for a different queue.
The readNotification and writeNotification parameters tell which bits in the event flag should be used to signal reads and writes on that queue. If the readNotification value is 0, the call will not fail, but a successful read will not set any notification bits.
In a synchronized queue, this would mean that the corresponding writeBlocking call will never wake up unless the bit is set elsewhere. In an unsynchronized queue, writeBlocking will not wait it should still be used to set the write notification bit , and it is appropriate for reads to not set any notification bits.
Similarly, writeblocking will fail if readNotification is 0, and a successful write sets the specified writeNotification bits. To wait on multiple queues at once, use an EventFlag object's wait method to wait on a bitmask of notifications.
0コメント