Recommit "[Support] Add RetryAfterSignal helper function"

The difference from the previous version is the use of decltype, as the
implementation of std::result_of in libc++ did not work correctly for
variadic function like open(2).

Original summary:
This function retries an operation if it was interrupted by a signal
(failed with EINTR). It's inspired by the TEMP_FAILURE_RETRY macro in
glibc, but I've turned that into a template function. I've also added a
fail-value argument, to enable the function to be used with e.g.
fopen(3), which is documented to fail for any reason that open(2) can
fail (which includes EINTR).

The main user of this function will be lldb, but there were also a
couple of uses within llvm that I could simplify using this function.

Reviewers: zturner, silvas, joerg

Subscribers: mgorny, llvm-commits

Differential Revision: https://reviews.llvm.org/D33895

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306671 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/Support/Errno.h b/include/llvm/Support/Errno.h
index 4ce65e7..35dc1ea 100644 (file)
--- a/include/llvm/Support/Errno.h
+++ b/include/llvm/Support/Errno.h
@@ -16,6 +16,7 @@
 
 #include <cerrno>
 #include <string>
+#include <type_traits>
 
 namespace llvm {
 namespace sys {
@@ -29,6 +30,16 @@ std::string StrError();
 /// Like the no-argument version above, but uses \p errnum instead of errno.
 std::string StrError(int errnum);
 
+template <typename FailT, typename Fun, typename... Args>
+inline auto RetryAfterSignal(const FailT &Fail, const Fun &F,
+                             const Args &... As) -> decltype(F(As...)) {
+  decltype(F(As...)) Res;
+  do
+    Res = F(As...);
+  while (Res == Fail && errno == EINTR);
+  return Res;
+}
+
 }  // namespace sys
 }  // namespace llvm
 

diff --git a/lib/Support/MemoryBuffer.cpp b/lib/Support/MemoryBuffer.cpp
index 227e792..85e782b 100644 (file)
--- a/lib/Support/MemoryBuffer.cpp
+++ b/lib/Support/MemoryBuffer.cpp
@@ -240,11 +240,9 @@ getMemoryBufferForStream(int FD, const Twine &BufferName) {
   // Read into Buffer until we hit EOF.
   do {
     Buffer.reserve(Buffer.size() + ChunkSize);
-    ReadBytes = read(FD, Buffer.end(), ChunkSize);
-    if (ReadBytes == -1) {
-      if (errno == EINTR) continue;
+    ReadBytes = sys::RetryAfterSignal(-1, read, FD, Buffer.end(), ChunkSize);
+    if (ReadBytes == -1)
       return std::error_code(errno, std::generic_category());
-    }
     Buffer.set_size(Buffer.size() + ReadBytes);
   } while (ReadBytes != 0);
 
@@ -391,13 +389,12 @@ getOpenFileImpl(int FD, const Twine &Filename, uint64_t FileSize,
 
   while (BytesLeft) {
 #ifdef HAVE_PREAD
-    ssize_t NumRead = ::pread(FD, BufPtr, BytesLeft, MapSize-BytesLeft+Offset);
+    ssize_t NumRead = sys::RetryAfterSignal(-1, ::pread, FD, BufPtr, BytesLeft,
+                                            MapSize - BytesLeft + Offset);
 #else
-    ssize_t NumRead = ::read(FD, BufPtr, BytesLeft);
+    ssize_t NumRead = sys::RetryAfterSignal(-1, ::read, FD, BufPtr, BytesLeft);
 #endif
     if (NumRead == -1) {
-      if (errno == EINTR)
-        continue;
       // Error while reading.
       return std::error_code(errno, std::generic_category());
     }

diff --git a/lib/Support/Unix/Path.inc b/lib/Support/Unix/Path.inc
index b677469..45097eb 100644 (file)
--- a/lib/Support/Unix/Path.inc
+++ b/lib/Support/Unix/Path.inc
@@ -737,10 +737,8 @@ std::error_code openFileForRead(const Twine &Name, int &ResultFD,
 #ifdef O_CLOEXEC
   OpenFlags |= O_CLOEXEC;
 #endif
-  while ((ResultFD = open(P.begin(), OpenFlags)) < 0) {
-    if (errno != EINTR)
-      return std::error_code(errno, std::generic_category());
-  }
+  if ((ResultFD = sys::RetryAfterSignal(-1, open, P.begin(), OpenFlags)) < 0)
+    return std::error_code(errno, std::generic_category());
 #ifndef O_CLOEXEC
   int r = fcntl(ResultFD, F_SETFD, FD_CLOEXEC);
   (void)r;
@@ -800,10 +798,8 @@ std::error_code openFileForWrite(const Twine &Name, int &ResultFD,
 
   SmallString<128> Storage;
   StringRef P = Name.toNullTerminatedStringRef(Storage);
-  while ((ResultFD = open(P.begin(), OpenFlags, Mode)) < 0) {
-    if (errno != EINTR)
-      return std::error_code(errno, std::generic_category());
-  }
+  if ((ResultFD = sys::RetryAfterSignal(-1, open, P.begin(), OpenFlags, Mode)) < 0)
+    return std::error_code(errno, std::generic_category());
 #ifndef O_CLOEXEC
   int r = fcntl(ResultFD, F_SETFD, FD_CLOEXEC);
   (void)r;

diff --git a/lib/Support/Unix/Process.inc b/lib/Support/Unix/Process.inc
index 1d0143c..2d46620 100644 (file)
--- a/lib/Support/Unix/Process.inc
+++ b/lib/Support/Unix/Process.inc
@@ -207,13 +207,10 @@ std::error_code Process::FixupStandardFileDescriptors() {
   for (int StandardFD : StandardFDs) {
     struct stat st;
     errno = 0;
-    while (fstat(StandardFD, &st) < 0) {
+    if (RetryAfterSignal(-1, fstat, StandardFD, &st) < 0) {
       assert(errno && "expected errno to be set if fstat failed!");
       // fstat should return EBADF if the file descriptor is closed.
-      if (errno == EBADF)
-        break;
-      // retry fstat if we got EINTR, otherwise bubble up the failure.
-      if (errno != EINTR)
+      if (errno != EBADF)
         return std::error_code(errno, std::generic_category());
     }
     // if fstat succeeds, move on to the next FD.
@@ -222,11 +219,8 @@ std::error_code Process::FixupStandardFileDescriptors() {
     assert(errno == EBADF && "expected errno to have EBADF at this point!");
 
     if (NullFD < 0) {
-      while ((NullFD = open("/dev/null", O_RDWR)) < 0) {
-        if (errno == EINTR)
-          continue;
+      if ((NullFD = RetryAfterSignal(-1, open, "/dev/null", O_RDWR)) < 0)
         return std::error_code(errno, std::generic_category());
-      }
     }
 
     if (NullFD == StandardFD)

diff --git a/unittests/Support/CMakeLists.txt b/unittests/Support/CMakeLists.txt
index e2a6561..641163e 100644 (file)
--- a/unittests/Support/CMakeLists.txt
+++ b/unittests/Support/CMakeLists.txt
@@ -21,6 +21,7 @@ add_llvm_unittest(SupportTests
   DebugTest.cpp
   EndianStreamTest.cpp
   EndianTest.cpp
+  ErrnoTest.cpp
   ErrorOrTest.cpp
   ErrorTest.cpp
   FileOutputBufferTest.cpp

diff --git a/unittests/Support/ErrnoTest.cpp b/unittests/Support/ErrnoTest.cpp
new file mode 100644 (file)
index 0000000..67f834a
--- /dev/null
+++ b/unittests/Support/ErrnoTest.cpp
@@ -0,0 +1,36 @@
+//===- ErrnoTest.cpp - Error handling unit tests --------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/Errno.h"
+#include "gtest/gtest.h"
+
+using namespace llvm::sys;
+
+TEST(ErrnoTest, RetryAfterSignal) {
+  EXPECT_EQ(1, RetryAfterSignal(-1, [] { return 1; }));
+
+  EXPECT_EQ(-1, RetryAfterSignal(-1, [] {
+    errno = EAGAIN;
+    return -1;
+  }));
+  EXPECT_EQ(EAGAIN, errno);
+
+  unsigned calls = 0;
+  EXPECT_EQ(1, RetryAfterSignal(-1, [&calls] {
+              errno = EINTR;
+              ++calls;
+              return calls == 1 ? -1 : 1;
+            }));
+  EXPECT_EQ(2u, calls);
+
+  EXPECT_EQ(1, RetryAfterSignal(-1, [](int x) { return x; }, 1));
+
+  std::unique_ptr<int> P(RetryAfterSignal(nullptr, [] { return new int(47); }));
+  EXPECT_EQ(47, *P);
+}