diff options
Diffstat (limited to 'file_io/win32/readwrite.c')
| -rw-r--r-- | file_io/win32/readwrite.c | 33 |
1 files changed, 33 insertions, 0 deletions
diff --git a/file_io/win32/readwrite.c b/file_io/win32/readwrite.c index 5c2171dfa..efa5b04c1 100644 --- a/file_io/win32/readwrite.c +++ b/file_io/win32/readwrite.c @@ -308,6 +308,39 @@ APR_DECLARE(apr_status_t) apr_file_write(apr_file_t *thefile, const void *buf, a rv = WriteFile(thefile->filehand, buf, (DWORD)*nbytes, &bwrote, thefile->pOverlapped); } + else if (thefile->append && !thefile->pOverlapped) { + OVERLAPPED ov = {0}; + + /* If the file is opened for synchronous I/O, take advantage of the + * documented way to atomically append data by calling WriteFile() + * with both the OVERLAPPED.Offset and OffsetHigh members set to + * 0xFFFFFFFF. This avoids calling LockFile() that is otherwise + * required to avoid a race condition between seeking to the end + * and writing data. Not locking the file improves robustness of + * such appends and avoids a deadlock when appending to an already + * locked file, as described in PR50058. + * + * We use this approach only for files opened for synchronous I/O + * because in this case the I/O Manager maintains the current file + * position. Otherwise, the file offset returned or changed by + * the SetFilePointer() API is not guaranteed to be valid and that + * could, for instance, break apr_file_seek() calls after appending + * data. Sadly, if a file is opened for asynchronous I/O, this + * call doesn't update the OVERLAPPED.Offset member to reflect the + * actual offset used when appending the data (which we could then + * use to make seeking and other operations involving filePtr work). + * Therefore, when appending to files opened for asynchronous I/O, + * we still use the LockFile + SetFilePointer + WriteFile approach. + * + * References: + * https://bz.apache.org/bugzilla/show_bug.cgi?id=50058 + * https://msdn.microsoft.com/en-us/library/windows/desktop/aa365747 + * https://msdn.microsoft.com/en-us/library/windows/hardware/ff567121 + */ + ov.Offset = MAXDWORD; + ov.OffsetHigh = MAXDWORD; + rv = WriteFile(thefile->filehand, buf, (DWORD)*nbytes, &bwrote, &ov); + } else { apr_off_t offset = 0; apr_status_t rc; |