[llvm] r255837 - Drop an unnecessary use of writev.

[Rafael Espindola via llvm-commits]

Author: rafael
Date: Wed Dec 16 16:59:06 2015
New Revision: 255837

URL: http://llvm.org/viewvc/llvm-project?rev=255837&view=rev
Log:
Drop an unnecessary use of writev.

It looks like the code this patch deletes is based on a misunderstanding of
what guarantees writev provides. In particular, writev with 1 iovec is
not "more atomic" than a write.

Testing on OS X shows that both write and writev from multiple processes
can be intermixed.

Modified:
    llvm/trunk/include/llvm/Support/raw_ostream.h
    llvm/trunk/lib/Support/raw_ostream.cpp

Modified: llvm/trunk/include/llvm/Support/raw_ostream.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/raw_ostream.h?rev=255837&r1=255836&r2=255837&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Support/raw_ostream.h (original)
+++ llvm/trunk/include/llvm/Support/raw_ostream.h Wed Dec 16 16:59:06 2015
@@ -349,10 +349,6 @@ class raw_fd_ostream : public raw_pwrite
   ///
   bool Error;
 
-  /// Controls whether the stream should attempt to use atomic writes, when
-  /// possible.
-  bool UseAtomicWrites;
-
   uint64_t pos;
 
   bool SupportsSeeking;
@@ -402,16 +398,6 @@ public:
   /// to the offset specified from the beginning of the file.
   uint64_t seek(uint64_t off);
 
-  /// Set the stream to attempt to use atomic writes for individual output
-  /// routines where possible.
-  ///
-  /// Note that because raw_ostream's are typically buffered, this flag is only
-  /// sensible when used on unbuffered streams which will flush their output
-  /// immediately.
-  void SetUseAtomicWrites(bool Value) {
-    UseAtomicWrites = Value;
-  }
-
   raw_ostream &changeColor(enum Colors colors, bool bold=false,
                            bool bg=false) override;
   raw_ostream &resetColor() override;

Modified: llvm/trunk/lib/Support/raw_ostream.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/raw_ostream.cpp?rev=255837&r1=255836&r2=255837&view=diff
==============================================================================
--- llvm/trunk/lib/Support/raw_ostream.cpp (original)
+++ llvm/trunk/lib/Support/raw_ostream.cpp Wed Dec 16 16:59:06 2015
@@ -517,7 +517,7 @@ raw_fd_ostream::raw_fd_ostream(StringRef
 /// closes the file when the stream is destroyed.
 raw_fd_ostream::raw_fd_ostream(int fd, bool shouldClose, bool unbuffered)
     : raw_pwrite_stream(unbuffered), FD(fd), ShouldClose(shouldClose),
-      Error(false), UseAtomicWrites(false) {
+      Error(false) {
   if (FD < 0 ) {
     ShouldClose = false;
     return;
@@ -568,21 +568,7 @@ void raw_fd_ostream::write_impl(const ch
   pos += Size;
 
   do {
-    ssize_t ret;
-
-    // Check whether we should attempt to use atomic writes.
-    if (LLVM_LIKELY(!UseAtomicWrites)) {
-      ret = ::write(FD, Ptr, Size);
-    } else {
-      // Use ::writev() where available.
-#if defined(HAVE_WRITEV)
-      const void *Addr = static_cast<const void *>(Ptr);
-      struct iovec IOV = {const_cast<void *>(Addr), Size };
-      ret = ::writev(FD, &IOV, 1);
-#else
-      ret = ::write(FD, Ptr, Size);
-#endif
-    }
+    ssize_t ret = ::write(FD, Ptr, Size);
 
     if (ret < 0) {
       // If it's a recoverable error, swallow it and retry the write.