Add POSIX shared memory support for Mac

base/memory/shared_memory_helper.cc

+// Copyright (c) 2016 The Chromium Authors. All rights reserved.

[Alexei Svitkine (slow), 2016/12/09 18:04:15]

Nit: No (c)

[lawrencewu, 2016/12/09 18:33:57]

Done.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/memory/shared_memory_helper.h"
+
+#include "base/threading/thread_restrictions.h"
+
+namespace base {
+
+#if !defined(OS_ANDROID)
+bool CreateAnonymousSharedMemory(const SharedMemoryCreateOptions& options,
+                                 ScopedFILE* fp,
+                                 ScopedFD* readonly_fd,
+                                 FilePath* path) {
+#if !(defined(OS_MACOSX) && !defined(OS_IOS))
+  // It doesn't make sense to have a open-existing private piece of shmem
+  DCHECK(!options.open_existing_deprecated);
+#endif  // !(defined(OS_MACOSX) && !defined(OS_IOS)
+  // Q: Why not use the shm_open() etc. APIs?
+  // A: Because they're limited to 4mb on OS X.  FFFFFFFUUUUUUUUUUU
+  FilePath directory;
+  ScopedPathUnlinker path_unlinker;
+  if (GetShmemTempDir(options.executable, &directory)) {
+    fp->reset(base::CreateAndOpenTemporaryFileInDir(directory, path));
+
+    // Deleting the file prevents anyone else from mapping it in (making it
+    // private), and prevents the need for cleanup (once the last fd is
+    // closed, it is truly freed).
+    if (*fp)
+      path_unlinker.reset(path);
+  }
+
+  if (*fp) {
+    if (options.share_read_only) {

[Alexei Svitkine (slow), 2016/12/09 18:04:15]

Nit: Combine with the above if.

[lawrencewu, 2016/12/09 18:33:57]

Done.

+      // Also open as readonly so that we can ShareReadOnlyToProcess.
+      readonly_fd->reset(HANDLE_EINTR(open(path->value().c_str(), O_RDONLY)));
+      if (!readonly_fd->is_valid()) {
+        DPLOG(ERROR) << "open(\"" << path->value() << "\", O_RDONLY) failed";
+        fp->reset();
+        return false;
+      }
+    }
+  }
+  return true;
+}
+
+bool PrepareMapFile(ScopedFILE fp, ScopedFD readonly_fd, int* mapped_file,
+                    int* readonly_mapped_file) {
+  DCHECK_EQ(-1, *mapped_file);
+  DCHECK_EQ(-1, *readonly_mapped_file);
+  if (fp == NULL)
+    return false;
+
+  // This function theoretically can block on the disk, but realistically
+  // the temporary files we create will just go into the buffer cache
+  // and be deleted before they ever make it out to disk.
+  base::ThreadRestrictions::ScopedAllowIO allow_io;
+
+  struct stat st = {};
+  if (fstat(fileno(fp.get()), &st))
+    NOTREACHED();
+  if (readonly_fd.is_valid()) {
+    struct stat readonly_st = {};
+    if (fstat(readonly_fd.get(), &readonly_st))
+      NOTREACHED();
+    if (st.st_dev != readonly_st.st_dev || st.st_ino != readonly_st.st_ino) {
+      LOG(ERROR) << "writable and read-only inodes don't match; bailing";
+      return false;
+    }
+  }
+
+  *mapped_file = HANDLE_EINTR(dup(fileno(fp.get())));
+  if (*mapped_file == -1) {
+    if (errno == EMFILE) {
+      LOG(WARNING) << "Shared memory creation failed; out of file descriptors";
+      return false;
+    } else {

[Alexei Svitkine (slow), 2016/12/09 18:04:15]

Nit: No else since you return above.

[lawrencewu, 2016/12/09 18:33:57]

Done.

+      NOTREACHED() << "Call to dup failed, errno=" << errno;
+    }
+  }
+  *readonly_mapped_file = readonly_fd.release();
+
+  return true;
+}
+#endif  // !defined(OS_ANDROID)
+
+}  // namespace base