[profile] Fix file contention causing dropped counts on Windows under -fprofile-generate

See PR43425:
https://bugs.llvm.org/show_bug.cgi?id=43425

When writing profile data on Windows we were opening profile file with
exclusive read/write access.

In case we are trying to write to the file from multiple processes
simultaneously, subsequent calls to CreateFileA would return
INVALID_HANDLE_VALUE.

To fix this, I changed to open without exclusive access and then take a
lock.

Patch by Michael Holman!

Differential revision: https://reviews.llvm.org/D70330

1 files changed, 7 insertions, 2 deletions

diff --git a/compiler-rt/lib/profile/InstrProfilingUtil.c b/compiler-rt/lib/profile/InstrProfilingUtil.c
index 13301f341fc..bf5a9670fe1 100644
--- a/compiler-rt/lib/profile/InstrProfilingUtil.c
+++ b/compiler-rt/lib/profile/InstrProfilingUtil.c
@@ -207,8 +207,9 @@ COMPILER_RT_VISIBILITY FILE *lprofOpenFileEx(const char *ProfileName) {
   f = fdopen(fd, "r+b");
 #elif defined(_WIN32)
   // FIXME: Use the wide variants to handle Unicode filenames.
-  HANDLE h = CreateFileA(ProfileName, GENERIC_READ | GENERIC_WRITE, 0, 0,
-                         OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, 0);
+  HANDLE h = CreateFileA(ProfileName, GENERIC_READ | GENERIC_WRITE,
+                         FILE_SHARE_READ | FILE_SHARE_WRITE, 0, OPEN_ALWAYS,
+                         FILE_ATTRIBUTE_NORMAL, 0);
   if (h == INVALID_HANDLE_VALUE)
     return NULL;
 
@@ -218,6 +219,10 @@ COMPILER_RT_VISIBILITY FILE *lprofOpenFileEx(const char *ProfileName) {
     return NULL;
   }
 
+  if (lprofLockFd(fd) != 0)
+    PROF_WARN("Data may be corrupted during profile merging : %s\n",
+              "Fail to obtain file lock due to system limit.");
+
   f = _fdopen(fd, "r+b");
   if (f == 0) {
     CloseHandle(h);