commit | df61c0c3a3de070c7f7a714ef8758a248bf97263 | [log] [tgz] |
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author | Chris Dickens <christopher.a.dickens@gmail.com> | Wed Jan 22 11:06:29 2020 -0800 |
committer | Chris Dickens <christopher.a.dickens@gmail.com> | Wed Jan 22 11:13:20 2020 -0800 |
tree | 7251a4265a53da2e698cd4ce2a30b68460c26265 | |
parent | 13a2748b0796ad55ae0bfbfb6f2f11d552145331 [diff] |
Windows: Improve poll abstraction Commit 395e5a8a6f ("windows: remove total fds (256) limitations") and commit c730a8410c ("windows: workaround WaitForMultipleObjects max 64 events limitation.") lifted some hard-coded limits in the number of HANDLEs that can be used within the library. This change improves on these changes to make them more efficient. A bitmap has been added to provide an efficient lookup mechanism for located unused file descriptor indices. This avoids the O(n) lookup time for traversing the entire fd_table. This bitmap is dynamically resized along with the fd_table. The incremental size of the fd_table has been reduced from 256 to 64. The vast majority of applications won't need to use 256 HANDLEs, so we can optimize memory usage a bit. Commit fb864b7cde ("fix windows crash when multi-thread do sync transfer") added usbi_inc_fds_ref() and usbi_dec_fds_ref() functions to work around a reference count issue. Remove these functions and change the implementation of usbi_poll() to take a reference to each file descriptor upon entry and drop the references when returning. If the application experiences any kind of crash, there is a problem elsewhere. Finally, make the thread executing usbi_poll() take part in the waiting. The original implementation had this thread simply waiting on a single event while separate threads waited on the HANDLEs. Now this thread will wait on MAXIMUM_WAIT_OBJECTS - 1 HANDLEs, thereby reducing the number of threads that are created. Additionally there is now only a single event object that is shared amongst all waiting threads. Signed-off-by: Chris Dickens <christopher.a.dickens@gmail.com>
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