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@ -2493,6 +2493,14 @@ C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise, |
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it is assumed that all these functions actually work on fds, even |
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on win32. Should not be defined on non-win32 platforms. |
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=item EV_FD_TO_WIN32_HANDLE |
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If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map |
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file descriptors to socket handles. When not defining this symbol (the |
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default), then libev will call C<_get_osfhandle>, which is usually |
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correct. In some cases, programs use their own file descriptor management, |
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in which case they can provide this function to map fds to socket handles. |
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=item EV_USE_POLL |
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If defined to be C<1>, libev will compile in support for the C<poll>(2) |
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@ -2774,6 +2782,73 @@ watchers becomes O(1) w.r.t. prioritiy handling. |
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=back |
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=head1 Win32 platform limitations and workarounds |
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Win32 doesn't support any of the standards (e.g. POSIX) that libev |
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requires, and its I/O model is fundamentally incompatible with the POSIX |
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model. Libev still offers limited functionality on this platform in |
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the form of the C<EVBACKEND_SELECT> backend, and only supports socket |
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descriptors. This only applies when using Win32 natively, not when using |
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e.g. cygwin. |
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There is no supported compilation method available on windows except |
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embedding it into other applications. |
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Due to the many, low, and arbitrary limits on the win32 platform and the |
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abysmal performance of winsockets, using a large number of sockets is not |
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recommended (and not reasonable). If your program needs to use more than |
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a hundred or so sockets, then likely it needs to use a totally different |
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implementation for windows, as libev offers the POSIX model, which cannot |
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be implemented efficiently on windows (microsoft monopoly games). |
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=over 4 |
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=item The winsocket select function |
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The winsocket C<select> function doesn't follow POSIX in that it requires |
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socket I<handles> and not socket I<file descriptors>. This makes select |
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very inefficient, and also requires a mapping from file descriptors |
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to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>, |
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C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor |
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symbols for more info. |
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The configuration for a "naked" win32 using the microsoft runtime |
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libraries and raw winsocket select is: |
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#define EV_USE_SELECT 1 |
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#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */ |
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Note that winsockets handling of fd sets is O(n), so you can easily get a |
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complexity in the O(n²) range when using win32. |
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=item Limited number of file descriptors |
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Windows has numerous arbitrary (and low) limits on things. Early versions |
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of winsocket's select only supported waiting for a max. of C<64> handles |
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(probably owning to the fact that all windows kernels can only wait for |
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C<64> things at the same time internally; microsoft recommends spawning a |
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chain of threads and wait for 63 handles and the previous thread in each). |
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Newer versions support more handles, but you need to define C<FD_SETSIZE> |
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to some high number (e.g. C<2048>) before compiling the winsocket select |
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call (which might be in libev or elsewhere, for example, perl does its own |
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select emulation on windows). |
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Another limit is the number of file descriptors in the microsoft runtime |
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libraries, which by default is C<64> (there must be a hidden I<64> fetish |
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or something like this inside microsoft). You can increase this by calling |
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C<_setmaxstdio>, which can increase this limit to C<2048> (another |
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arbitrary limit), but is broken in many versions of the microsoft runtime |
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libraries. |
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This might get you to about C<512> or C<2048> sockets (depending on |
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windows version and/or the phase of the moon). To get more, you need to |
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wrap all I/O functions and provide your own fd management, but the cost of |
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calling select (O(n²)) will likely make this unworkable. |
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=back |
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=head1 AUTHOR |
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Marc Lehmann <libev@schmorp.de>. |
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