When there is a fast producer and slow consumer, I want to replace all old waiting emissions with the newest one - something similar to RxJava's Emitter.BackpressureMode.LATEST
Is there any way to achieve this in RxDart or Dart Streams?
Hi it seems like I'm too late)
But maybe it will help someone else
For back pressure in rxDart there is the Debounce method.
Example:
subject.debounce(new Duration(milliseconds: 500)).listen((s) => print(s));
More info:
https://www.youtube.com/watch?v=u9VgxH-X_7s
Related
I'm trying to send packets over CoAP between two TI 2650 sensortags. I used the logic from the "er-rest-example" provided by contiki 3.0, that is:
coap_init_message(request, COAP_TYPE_CON, COAP_POST, 0);
coap_set_header_uri_path(request, url);
coap_set_payload(request, (uint8_t*)msg, sizeof(msg) - 1);
COAP_BLOCKING_REQUEST(&server_ip, REMOTE_PORT, request, client_chunk_handler);
When I started the program, it works as expected until the first time COAP_BLOCKING_REQUEST is called, at which point the program seems to freeze (doesn't react to button presses anymore).
So I assume COAP_BLOCKING_REQUEST blocks until it receives a response, which is not suitable for my project. Can anyone confirm that?
UPDATE:
Going forward from that assumption, my question now is, what steps to I have to take to send out a packet?
Do I use the coap_send_message function from er-coap.c or the coap_send_transaction function from er-coap-transaction.c?
I want to figure out what functions I have to call in which order to configure the packet correctly and then send it out with the correct function (which I guess would be one of the above).
Maybe there is some documentation out there that I haven't found yet and someone could point me to it?
Cheers
I'm trying to do something like this:
"Main.R"
for( i in ...){
...
...
source("file.R")
}
The problem is that when I'm running Main.R, It uses all memory RAM because file.R doesn't stop and it is creating a lot of them. (Sorry for my english).
So I get a message on Windows saying that memory couldn't read and write...
How can I fix this? Can I close ONLY file.R when it finishes?
PS:file.R call another scripts...
Thanks a lot.
You can use gc() during or after running of your function to release some memory. Also after rm() it may be useful.
The problem is that I was using pararell so at the end of file.RI have written stopCluster(cl) and the task close after that.
I would like to know when the user from a command line presses control-c so I can save some stuff.
How do I do this? I've looked but haven't really seen anything.
Note: I'm somewhat familiar with lua, but I'm no expert. I mostly use lua to use the library Torch (http://torch.ch/)
Implementing a SIGINT handler is straightforward using the excellent luaposix library:
local signal = require("posix.signal")
signal.signal(signal.SIGINT, function(signum)
io.write("\n")
-- put code to save some stuff here
os.exit(128 + signum)
end)
Refer to the posix.signal module's API documentation for more information.
There exists io libraries that support this.
I know zmq and libuv
Libuv example with lluv binding - https://github.com/moteus/lua-lluv/blob/master/examples/sig.lua
ZeroMQ return EINTR from poll function when user press Ctrl-C
But I do not handle thi byself
windows : SetConsoleCtrlHandler
linux : signal
There are two behaviors of the signal which are undesirable, which will cause complexities in the code.
Program termination
Broken IO
The first behavior can be caught and remembered in a C program by using SetConsoleCtrlHandler/signal. This will allow your function to be called, and you can remember that the system needs to shutdown. Then at some point in the lua code you see it has happened (call to check), and perform your tidy up and shutdown.
The second behavior, is that a blocking operation (read/write) will be cancelled by the signal, and the operation will be unfinished. That would need to be checked at each IO event, and then re-started, or cancelled as appropriate.
require('sys')
sys.catch_ctrl_c()
I use this to catch the exit from cli.
I'm playing with a tiny web server and I'm implementing one version using the async package, and one synchronous version executing each request in a separate isolate. I would like to simply pipe a file stream to the HttpResponse, but I can't do that synchronously. And I can't find a way to wait for neither the Stream nor a Future synchronously. I'm now using a RandomAccessFile instead which works, but it becomes messier.
One solution would be to execute a periodical timer to check if the future is completed (by setting a boolean or similar), but that is most definitely not something I want to use.
Is there a way to wait synchronously for a Future and a Stream? If not, why?
For future visitors coming here simply wanting to perform some task after a Future or Stream completes, use await and await for inside an async method.
Future
final myInt = await getFutureInt();
Stream
int mySum = 0;
await for (int someInt in myIntStream) {
mySum += someInt;
}
Note
This may be technically different than performing a synchronous task, but it achieves the goal of completing one task before doing another one.
AFAIK there isn't a way to wait synchronously for a Future or a Stream. Why? Because these are asynchronous pretty much definitionally, and as you are discovering, the APIs are designed with asynchronous behavior in mind.
There are a couple of Future constructors, Future.value() and Future.sync(), that execute immediately, but I don't think these are probably what you have in mind.
NB: The entire code base for this project is so large that posting any meaningful amount wold render this question too localised, I have tried to distil any code down to the bare-essentials. I'm not expecting anyone to solve my problems directly but I will up vote those answers I find helpful or intriguing.
This project uses a modified version of AudioStreamer to playback audio files that are saved to locally to the device (iPhone).
The stream is set up and scheduled on the current loop using this code (unaltered from the standard AudioStreamer project as far as I know):
CFStreamClientContext context = {0, self, NULL, NULL, NULL};
CFReadStreamSetClient(
stream,
kCFStreamEventHasBytesAvailable | kCFStreamEventErrorOccurred | kCFStreamEventEndEncountered,
ASReadStreamCallBack,
&context);
CFReadStreamScheduleWithRunLoop(stream, CFRunLoopGetCurrent(), kCFRunLoopCommonModes);
The ASReadStreamCallBack calls:
- (void)handleReadFromStream:(CFReadStreamRef)aStream
eventType:(CFStreamEventType)eventType
On the AudioStreamer object, this all works fine until the stream is read using this code:
BOOL hasBytes = NO; //Added for debugging
hasBytes = CFReadStreamHasBytesAvailable(stream);
length = CFReadStreamRead(stream, bytes, kAQDefaultBufSize);
hasBytes is YES but when CFReadStreamRead is called execution stops, the App does not crash it just stops exciting, any break points below the CFReadStreamRead call are not hit and ASReadStreamCallBack is not called again.
I am at a loss to what might cause this, my best guess is the thread is being terminated? But the hows and whys is why I'm asking SO.
Has anyone seen this behaviour before? How can I track it down and ideas on how I might solve it will be very much welcome!
Additional Info Requested via Comments
This is 100% repeatable
CFReadStreamHasBytesAvailable was added by me for debugging but removing it has no effect
First, I assume that CFReadStreamScheduleWithRunLoop() is running on the same thread as CFReadStreamRead()?
Is this thread processing its runloop? Failure to do this is my main suspicion. Do you have a call like CFRunLoopRun() or equivalent on this thread?
Typically there is no reason to spawn a separate thread for reading streams asynchronously, so I'm a little confused about your threading design. Is there really a background thread involved here? Also, typically CFReadStreamRead() would be in your client callback (when you receive the kCFStreamEventHasBytesAvailable event (which it appears to be in the linked code), but you're suggesting ASReadStreamCallBack is never called. How have you modified AudioStreamer?
It is possible that the stream pointer is just corrupt in some way. CFReadStreamRead should certainly not block if bytes are available (it certainly would never block for more than a few milliseconds for local files). Can you provide the code you use to create the stream?
Alternatively, CFReadStreams send messages asynchronously but it is possible (but not likely) that it's blocking because the runloop isn't being processed.
If you prefer, I've uploaded my AudioPlayer inspired by Matt's AudioStreamer hosted at https://code.google.com/p/audjustable/. It supports local files (as well as HTTP). I think it does what you wanted (stream files from more than just HTTP).