add shortcut around syscalls when file not found in win32_stat

win32_stat on success makes ~7 system calls, some from perl, some from CRT,
but on failure, typically file not found, the perl syscalls fails, then the
CRT stat runs, and fails too, so 5 mostly failing system calls are done
for file not found. If the perl syscall says file not found, the
file wont magically come into existence in the next 10-1000 us for the
CRT's syscalls, so skip calling the CRT and the additional syscalls
if the perl didn't find the file. This patch reduces the number of syscalls
from 5 to 1 for file not found for a win32 perl stat. Benchmark and
profiling info is attached to RT ticket for this patch. Note CreateFile on
a dir fails with ERROR_ACCESS_DENIED so in some cases, a failed CreateFile
is still a successful CRT stat() which does things differently so dirs can
be opened.

1 files changed, 8 insertions, 0 deletions

diff --git a/win32/win32.c b/win32/win32.c
index b410f662cd..651b97b417 100644
--- a/win32/win32.c
+++ b/win32/win32.c
@@ -1514,6 +1514,14 @@ win32_stat(const char *path, Stat_t *sbuf)
                 nlink = bhi.nNumberOfLinks;
             CloseHandle(handle);
         }
+	else {
+	    DWORD err = GetLastError();
+	    /* very common case, skip CRT stat and its also failing syscalls */
+	    if(err == ERROR_FILE_NOT_FOUND) {
+		errno = ENOENT;
+		return -1;
+	    }
+	}
     }
 
     /* path will be mapped correctly above */