The operation of select and pselect is identical, with three differences: Description i select uses a timeout that is a struct timeval with seconds and microsecondswhile pselect uses a struct timespec with seconds and nanoseconds. Three independent sets of file descriptors are watched. Those listed in readfds will be watched to see if characters become available for reading more precisely, to see if a read will not block; in particular, a file descriptor is also ready on end-of-file ,those in writefds will be watched to see if a write will not block, and those in exceptfds will be watched for exceptions.
The operation of select and pselect is identical, other than these three differences: Three independent sets of file descriptors are watched. The file descriptors listed in readfds will be watched to see if characters become available for reading more precisely, to see if a read will not block; in particular, a file descriptor is also ready on end-of- file.
The file descriptors in writefds will be watched to see if space is available for write though a large write may still block. The file descriptors in exceptfds will be watched for exceptional conditions.
On exit, each of the file descriptor sets is modified in place to indicate which file descriptors actually changed status.
select(3) - Linux man page Prolog This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux. are ready for writing, or have an exceptional condition pending. There are many other CLI audio players for Linux. MPlayer, for example, can play audio files from the command line. Music Player Daemon has many front ends but can also be used from the command line. write() writes up to count bytes from the buffer pointed buf to the file referred to by the file descriptor fd.
Thus, if using select within a loop, the sets must be reinitialized before each call. Each of the three file descriptor sets may be specified as NULL if no file descriptors are to be watched for the corresponding class of events.
Four macros are provided to manipulate the sets. The indicated file descriptors in each set are checked, up to this limit but see BUGS.
The timeout argument specifies the interval that select should block waiting for a file descriptor to become ready. The call will block until either: Note that the timeout interval will be rounded up to the system clock granularity, and kernel scheduling delays mean that the blocking interval may overrun by a small amount.
If both fields of the timeval structure are zero, then select returns immediately. This is useful for polling.
If timeout is NULL no timeoutselect can block indefinitely. Other than the difference in the precision of the timeout argument, the following pselect call: Then a test of this global flag followed by a call of select could hang indefinitely if the signal arrived just after the test but just before the call.
Some code calls select with all three sets empty, nfds zero, and a non-NULL timeout as a fairly portable way to sleep with subsecond precision.
On Linux, select modifies timeout to reflect the amount of time not slept; most other implementations do not do this. This causes problems both when Linux code which reads timeout is ported to other operating systems, and when code is ported to Linux that reuses a struct timeval for multiple select s in a loop without reinitializing it.
On error, -1 is returned, and errno is set to indicate the error; the file descriptor sets are unmodified, and timeout becomes undefined. Perhaps a file descriptor that was already closed, or one on which an error has occurred.
Prior to this, pselect was emulated in glibc but see BUGS. However, note that the System V variant typically sets the timeout variable before exit, but the BSD variant does not.
POSIX specifies this error for poll 2but not for select. On systems that lack pselectreliable and more portable signal trapping can be achieved using the self-pipe trick.
In this technique, a signal handler writes a byte to a pipe whose other end is monitored by select in the main program. On Linux and some other systemsclosing the file descriptor in another thread has no effect on select.select(3) - Linux man page Prolog This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux. are ready for writing, or have an exceptional condition pending.
I haven't written about using my Bluetooth devices on Linux in quite some time.
That is good, because it means that they are all just working so there is not a . On OS X and Linux, the root folder is /. If you want your programs to work on all operating systems, you will have to write your Python scripts to handle both cases. Fortunately, this is simple to do with the benjaminpohle.com() Its first argument is the list you want to select from; the second argument is the number of values you want to.
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