[PATCH] D70330: [profile] Fix file contention causing dropped counts on Windows under -fprofile-generate

[Michael Holman via Phabricator via llvm-commits]

Holman created this revision.
Holman added reviewers: davidxl, hans.
Herald added projects: Sanitizers, LLVM.
Herald added subscribers: llvm-commits, Sanitizers.

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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D70330

Files:
  compiler-rt/lib/profile/InstrProfilingUtil.c


Index: compiler-rt/lib/profile/InstrProfilingUtil.c
===================================================================
--- compiler-rt/lib/profile/InstrProfilingUtil.c
+++ compiler-rt/lib/profile/InstrProfilingUtil.c
@@ -207,8 +207,9 @@
   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 @@
     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);


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