On Fri, Jul 1, 2022 at 11:14 AM Ivan Zhakov <i...@visualsvn.com> wrote: > > On Fri, 1 Jul 2022 at 01:10, Yann Ylavic <ylavic....@gmail.com> wrote: > > > > On Fri, Jul 1, 2022 at 12:00 AM Yann Ylavic <ylavic....@gmail.com> wrote: > > > > > > On Thu, Jun 30, 2022 at 7:28 PM <i...@apache.org> wrote: > > > > > > > > Author: ivan > > > > Date: Thu Jun 30 17:28:50 2022 > > > > New Revision: 1902378 > > > > > > > > URL: http://svn.apache.org/viewvc?rev=1902378&view=rev > > > > Log: > > > > On 1.8.x branch: Merge r1806299, r1806301, r1806308, r1806610: > > > > *) apr_file_write: Optimize large writes to buffered files on > > > > Windows. > > > [] > > > > > > > > --- apr/apr/branches/1.8.x/file_io/win32/readwrite.c (original) > > > > +++ apr/apr/branches/1.8.x/file_io/win32/readwrite.c Thu Jun 30 > > > > 17:28:50 2022 > > > > @@ -247,6 +247,91 @@ APR_DECLARE(apr_status_t) apr_file_read( > > > > return rv; > > > > } > > > > > > > > +/* Helper function that adapts WriteFile() to apr_size_t instead > > > > + * of DWORD. */ > > > > +static apr_status_t write_helper(HANDLE filehand, const char *buf, > > > > + apr_size_t len, apr_size_t *pwritten) > > > > +{ > > > > + apr_size_t remaining = len; > > > > + > > > > + *pwritten = 0; > > > > + do { > > > > + DWORD to_write; > > > > + DWORD written; > > > > + > > > > + if (remaining > APR_DWORD_MAX) { > > > > + to_write = APR_DWORD_MAX; > > > > + } > > > > + else { > > > > + to_write = (DWORD)remaining; > > > > + } > > > > + > > > > + if (!WriteFile(filehand, buf, to_write, &written, NULL)) { > > > > + *pwritten += written; > > > > + return apr_get_os_error(); > > > > + } > > > > + > > > > + *pwritten += written; > > > > + remaining -= written; > > > > + buf += written; > > > > + } while (remaining); > > > > > > So there's no writev() like syscall on Windows (something that > > > provides atomicity)? > > > > I found WriteFileGather > > (https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-writefilegather). > > Maybe it can help with some logic à la apr_socket_sendv()? > > > [[[ > Each buffer must be at least the size of a system memory page and must be > aligned on a system memory page size boundary. The system writes one system > memory page of data from each buffer. > ]]] > [[[ > The total number of bytes to be written. Each element of aSegmentArray > contains a one-page chunk of this total. Because the file must be opened with > FILE_FLAG_NO_BUFFERING, the number of bytes must be a multiple of the sector > size of the file system where the file is located. > ]]]
OK, I said "found it" not "looked at it in detail" :) Too restrictive it seems (reminds me of O_DIRECT on unixes, we don't want to use it here). But the short-write argument stands, if Windows never short-writes then the implicit full-write is unnecessary, but if it does short-write then apr_file_write() has to return it too (for the user to know), so in both cases the loop has to stop when written < to_write (and probably return success if written > 0). Users that don't expect short-writes should use apr_file_write_full(). Same on the apr_file_read() side. Regards; Yann.
