nonblocking | 易学教程

Monitoring file using inotify

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问题 I am using inotify to monitor a local file, for example "/root/temp" using inotify_add_watch(fd, "/root/temp", mask). When this file is deleted, the program will be blocked by read(fd, buf, bufSize) function. Even if I create a new "/root/temp" file, the program is still block by read function. I am wondering if inotify can detect that the monitored file is created and the read function can get something from fd so that read will not be blocked forever. Here is my code: uint32_t mask = IN_ALL

How to read named FIFO non-blockingly?

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问题 I create a FIFO, and periodically open it in read-only and non-blockingly mode from a.py: os.mkfifo(cs_cmd_fifo_file, 0777) io = os.open(fifo, os.O_RDONLY | os.O_NONBLOCK) buffer = os.read(io, BUFFER_SIZE) From b.py, open the fifo for writing: out = open(fifo, 'w') out.write('sth') Then a.py will raise an error: buffer = os.read(io, BUFFER_SIZE) OSError: [Errno 11] Resource temporarily unavailable Anyone know what's wrong? 回答1: According to the manpage of read(2) : EAGAIN or EWOULDBLOCK The

Can regular file reading benefited from nonblocking-IO?

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It seems not to me and I found a link that supports my opinion . What do you think? The content of the link you posted is correct. A regular file socket, opened in non-blocking mode, will always be "ready" for reading; when you actually try to read it, blocking (or more accurately as your source points out, sleeping) will occur until the operation can succeed. In any case, I think your source needs some sedatives. One angry person, that is. I've been digging into this quite heavily for the past few hours and can attest that the author of the link you cited is correct. However, the appears to

When and how to use Tornado? When is it useless?

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问题 Ok, Tornado is non-blocking and quite fast and it can handle a lot of standing requests easily. But I guess it's not a silver bullet and if we just blindly run Django-based or any other site with Tornado it won't give any performance boost. I couldn't find comprehensive explanation of this, so I'm asking it here: When should Tornado be used? When is it useless? When using it, what should be taken into account? How can we make inefficient site using Tornado? There is a server and a

Non-blocking keyboard read - C/C++

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问题 I got this following function with me working now. But what I need to improve is that it would read input from the keyboard (on the terminal) EVEN THOUGH IT IS NOT BEING PRESSED. I need to know when it is NOT pressed (idle) so that the switch case block will fall into the default section. At this point, the read() function waits until there's an input from the user. Can anyone give a suggestion just based on modifying this following code? NOTE: I'm a Java programmer, and still learning C/C++

Opengl Unsynchronized/Non-blocking Map

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I just found the following OpenGL specification for ARB_map_buffer_range . I'm wondering if it is possible to do non-blocking map calls using this extension? Currently in my application im rendering to an FBO which I then map to a host PBO buffer. glMapBuffer(target_, GL_READ_ONLY); However, the problem with this is that it blocks the rendering thread while transferring the data. I could reduce this issue by pipelining the rendering, but latency is a big issue in my application. My question is whether i can use map_buffer_range with MAP_UNSYNCHRONIZED_BIT and wait for the map operation to

Can't seem to get a timeout working when connecting to a socket

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问题 I'm trying to supply a timeout for connect(). I've searched around and found several articles related to this. I've coded up what I believe should work but unfortunately I get no error reported from getsockopt(). But then when I come to the write() it fails with an errno of 107 - ENOTCONN. A couple of points. I'm running on Fedora 23. The docs for connect() says it should return failure with an errno of EINPROGRESS for a connect that is not complete yet however I was experiencing EAGAIN so I

Bash script with non-blocking read

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I want to send some data to a root process with a named pipe. Here is the script and it works great: #!/bin/sh pipe=/tmp/ntp if [[ ! -p $pipe ]]; then mknod -m 666 $pipe p fi while true do if read line <$pipe; then /root/netman/extra/bin/ntpclient -s -h $line > $pipe 2>&1 fi done I actually have several script like this one. I would like to enclose all of them in a single script. The problem is that execution blocks on the first "read" and I cannot execute multiple "reads" in a single process. Isn't there anything I can do? Is it possible to have a "non-blocking" bash read? Just put the

Is console output a blocking operation?

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When a Java program calls System.out.println() or a Scala program calls println() does the thread block? I'm writing a Scala program with a huge amount of subtasks. Each subtask is executed inside a Future. It is recommended that code inside actors and futures does not block, so that subsequent tasks don't have to wait, too. But I want to print very much on the console. And if it is a blocking operation: What can I do to optimize performance? Should I use a dedicated thread for console output, so that thread is the only one that blocks? Any other advices? Of course I could try to reduce the

If a web server is non-blocking, does this mean it is handling IO the same as node.js?

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I will soon be using a server named Undertow. The website says: Undertow is a flexible performant web server written in java, providing both blocking and non-blocking API’s based on NIO If Undertow allows non-blocking, is that the same as node.js? I don't mean the languages or anything like that. I have a separate project where I thought node.js would have been a good choice, but if I can use a single product for multiple projects it would be helpful. EDIT: I found this question. Java NIO non-blocking mode vs node.js asychronous operation And I am starting to think I have confused things.