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Most of the library only uses the monotonic clock. In fact, the only use
of the realtime clock is to implement the POSIX version of
usbi_cond_timedwait(). Now that Windows can no longer use the POSIX
thread abstraction, there is no need for Windows to implement a means of
reading the realtime clock.
This change replaces usbi_clock_gettime() with usbi_get_monotonic_time()
and usbi_get_real_time(). When clock_gettime() is available, both
functions are implemented as simple inline calls, otherwise the backend
must provide a definition for usbi_get_monotonic_time() *AND*
usbi_get_real_time() iff the platform is POSIX.
Reading the clocks is also never expected to fail. In practice, if it
ever did there would be much more than libusb that would not function
correctly. The new functions therefore have no return value, thus
allowing the callers to assume success and remove a bunch of error
handling code. The clock_gettime() wrappers have a simple error check
that is only enforced in debug builds.
This change also makes it unnecessary to check for and use
clock_gettime() on Windows, so remove it and always provide
usbi_get_monotonic_time().
Signed-off-by: Chris Dickens <christopher.a.dickens@gmail.com>
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The way in which system handles or resources are represented differs
greatly between Unix-like operating systems and Windows. Ever since
Windows support was added to libusb, Windows been emulating principles
of Unix-like operating systems such as file descriptors and poll().
This commit introduces an abstraction layer that completely removes the
need to perform any emulation. Fundamentally there are three things that
each platform provides to libusb:
1) A signallable event
2) A timer (not required, but useful)
3) A means to wait for event sources such as the above to be triggered
The POSIX abstraction for Unix-like operating systems uses file
descriptors as the "handles" to the underlying system resources. The
signallable event is implemented using a pipe, the timer as a timerfd
(where supported) and the poll() system call is used to wait for events.
The Windows abstraction uses native HANDLEs as the "handles" to the
underlying system resources. The signallable event is implemented using
a manual-reset event, the timer as a manual-reset waitable timer, and
the WaitForMultipleObjects() system call is used to wait for events.
Closes #252
Signed-off-by: Chris Dickens <christopher.a.dickens@gmail.com>
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