Add POSIX shared memory support for Mac

base/memory/shared_memory_mac.cc

Index: base/memory/shared_memory_mac.cc
diff --git a/base/memory/shared_memory_mac.cc b/base/memory/shared_memory_mac.cc
index a8f09555d96de9b6ab420b2123f5999cd8bf9223..c0488cbeac319dc36b3b249b41e7f0c3d2e820c6 100644
--- a/base/memory/shared_memory_mac.cc
+++ b/base/memory/shared_memory_mac.cc
@@ -4,22 +4,33 @@
 
 #include "base/memory/shared_memory.h"
 
+#include <errno.h>
+#include <fcntl.h>
 #include <mach/mach_vm.h>
+#include <stddef.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <unistd.h>
 
 #include "base/files/file_util.h"
 #include "base/files/scoped_file.h"
 #include "base/logging.h"
-#include "base/mac/foundation_util.h"
 #include "base/mac/mac_util.h"
 #include "base/mac/scoped_mach_vm.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_macros.h"
+#include "base/posix/eintr_wrapper.h"
+#include "base/posix/safe_strerror.h"
 #include "base/process/process_metrics.h"
 #include "base/profiler/scoped_tracker.h"
 #include "base/scoped_generic.h"
 #include "base/strings/utf_string_conversions.h"
 #include "build/build_config.h"
 
+#if defined(OS_MACOSX)
+#include "base/mac/foundation_util.h"
+#endif  // OS_MACOSX
+
 namespace base {
 
 namespace {
@@ -67,13 +78,84 @@ bool MakeMachSharedMemoryHandleReadOnly(SharedMemoryHandle* new_handle,
   return true;
 }
 
+struct ScopedPathUnlinkerTraits {
+  static FilePath* InvalidValue() { return nullptr; }
+
+  static void Free(FilePath* path) {
+    // TODO(erikchen): Remove ScopedTracker below once http://crbug.com/466437
+    // is fixed.
+    tracked_objects::ScopedTracker tracking_profile(

[Robert Sesek, 2016/12/06 21:45:55]

Do we still need the ScopedTrackers in this file?

[lawrencewu, 2016/12/06 22:33:24]

Probably not, now that the bug is fixed. erikchen@, can you confirm?

[lawrencewu, 2016/12/07 19:44:26]

Removed all instances of ScopedTracker.

+        FROM_HERE_WITH_EXPLICIT_FUNCTION(
+            "466437 SharedMemory::Create::Unlink"));
+    if (unlink(path->value().c_str()))
+      PLOG(WARNING) << "unlink";
+  }
+};
+
+// Unlinks the FilePath when the object is destroyed.
+typedef ScopedGeneric<FilePath*, ScopedPathUnlinkerTraits> ScopedPathUnlinker;
+
+// Makes a temporary file, fdopens it, and then unlinks it. |fp| is populated
+// with the fdopened FILE. |readonly_fd| is populated with the opened fd if
+// options.share_read_only is true. |path| is populated with the location of
+// the file before it was unlinked.
+// Returns false if there's an unhandled failure.
+bool CreateAnonymousSharedMemory(const SharedMemoryCreateOptions& options,
+                                 ScopedFILE* fp,
+                                 ScopedFD* readonly_fd,
+                                 FilePath* path) {
+  // Q: Why not use the shm_open() etc. APIs?
+  // A: Because they're limited to 4mb on OS X.  FFFFFFFUUUUUUUUUUU

[Robert Sesek, 2016/12/06 21:45:55]

Hmmmm. I wonder if we could use shm_open for this instead, since the 4mb limit
shouldn't be an issue. It may be faster than the unlink-tmp-file approach.

[lawrencewu, 2016/12/06 22:33:24]

I'd like to punt on this, since we can just reuse the POSIX code here and I
don't think I have time
to re-implement this using shm_open.

+  FilePath directory;
+  ScopedPathUnlinker path_unlinker;
+  if (GetShmemTempDir(options.executable, &directory)) {
+    // TODO(erikchen): Remove ScopedTracker below once http://crbug.com/466437
+    // is fixed.
+    tracked_objects::ScopedTracker tracking_profile(
+        FROM_HERE_WITH_EXPLICIT_FUNCTION(
+            "466437 SharedMemory::Create::OpenTemporaryFile"));
+    fp->reset(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) {
+      // TODO(erikchen): Remove ScopedTracker below once
+      // http://crbug.com/466437 is fixed.
+      tracked_objects::ScopedTracker tracking_profile(
+          FROM_HERE_WITH_EXPLICIT_FUNCTION(
+              "466437 SharedMemory::Create::OpenReadonly"));
+      // 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;
+}
+
 }  // namespace
 
 SharedMemory::SharedMemory()
-    : mapped_size_(0), memory_(NULL), read_only_(false), requested_size_(0) {}
+    : mapped_memory_mechanism_(SharedMemoryHandle::MACH),
+      readonly_mapped_file_(-1),
+      mapped_size_(0),
+      memory_(NULL),
+      read_only_(false),
+      requested_size_(0) {}
 
 SharedMemory::SharedMemory(const SharedMemoryHandle& handle, bool read_only)
     : shm_(handle),
+      mapped_memory_mechanism_(SharedMemoryHandle::POSIX),
+      readonly_mapped_file_(-1),
       mapped_size_(0),
       memory_(NULL),
       read_only_(read_only),
@@ -101,8 +183,7 @@ void SharedMemory::CloseHandle(const SharedMemoryHandle& handle) {
 
 // static
 size_t SharedMemory::GetHandleLimit() {
-  // This should be effectively unlimited on OS X.
-  return 10000;
+  return GetMaxFds();
 }
 
 // static
@@ -111,6 +192,12 @@ SharedMemoryHandle SharedMemory::DuplicateHandle(
   return handle.Duplicate();
 }
 
+// static
+int SharedMemory::GetFdFromSharedMemoryHandle(
+    const SharedMemoryHandle& handle) {
+  return handle.GetFileDescriptor().fd;
+}
+
 bool SharedMemory::CreateAndMapAnonymous(size_t size) {
   return CreateAnonymous(size) && Map(size);
 }
@@ -136,9 +223,42 @@ bool SharedMemory::Create(const SharedMemoryCreateOptions& options) {
   if (options.size > static_cast<size_t>(std::numeric_limits<int>::max()))
     return false;
 
-  shm_ = SharedMemoryHandle(options.size);
+  if (options.type == SharedMemoryHandle::MACH) {
+    shm_ = SharedMemoryHandle(options.size);
+    requested_size_ = options.size;
+    return shm_.IsValid();
+  }
+
+  // This function theoretically can block on the disk. Both profiling of real
+  // users and local instrumentation shows that this is a real problem.
+  // https://code.google.com/p/chromium/issues/detail?id=466437
+  base::ThreadRestrictions::ScopedAllowIO allow_io;
+
+  ScopedFILE fp;
+  ScopedFD readonly_fd;
+
+  FilePath path;
+  bool result = CreateAnonymousSharedMemory(options, &fp, &readonly_fd, &path);
+  if (!result)
+    return false;
+
+  if (!fp) {
+    PLOG(ERROR) << "Creating shared memory in " << path.value() << " failed";
+    return false;
+  }
+
+  // Get current size.
+  struct stat stat;
+  if (fstat(fileno(fp.get()), &stat) != 0)
+    return false;
+  const size_t current_size = stat.st_size;
+  if (current_size != options.size) {
+    if (HANDLE_EINTR(ftruncate(fileno(fp.get()), options.size)) != 0)
+      return false;
+  }
   requested_size_ = options.size;
-  return shm_.IsValid();
+
+  return PrepareMapFile(std::move(fp), std::move(readonly_fd));
 }
 
 bool SharedMemory::MapAt(off_t offset, size_t bytes) {
@@ -154,6 +274,7 @@ bool SharedMemory::MapAt(off_t offset, size_t bytes) {
     mapped_size_ = bytes;
     DCHECK_EQ(0U, reinterpret_cast<uintptr_t>(memory_) &
                       (SharedMemory::MAP_MINIMUM_ALIGNMENT - 1));
+    mapped_memory_mechanism_ = shm_.type_;
   } else {
     memory_ = NULL;
   }
@@ -165,16 +286,29 @@ bool SharedMemory::Unmap() {
   if (memory_ == NULL)
     return false;
 
-  mach_vm_deallocate(mach_task_self(),
-                     reinterpret_cast<mach_vm_address_t>(memory_),
-                     mapped_size_);
+  switch (mapped_memory_mechanism_) {
+    case SharedMemoryHandle::POSIX:
+      munmap(memory_, mapped_size_);
+      break;
+    case SharedMemoryHandle::MACH:
+      mach_vm_deallocate(mach_task_self(),
+                         reinterpret_cast<mach_vm_address_t>(memory_),
+                         mapped_size_);
+      break;
+  }
+
   memory_ = NULL;
   mapped_size_ = 0;
   return true;
 }
 
 SharedMemoryHandle SharedMemory::handle() const {
-  return shm_;
+  switch (shm_.type_) {
+    case SharedMemoryHandle::POSIX:
+      return SharedMemoryHandle(shm_.GetFileDescriptor().fd);
+    case SharedMemoryHandle::MACH:
+      return shm_;
+  }
 }
 
 SharedMemoryHandle SharedMemory::TakeHandle() {
@@ -186,34 +320,114 @@ SharedMemoryHandle SharedMemory::TakeHandle() {
 void SharedMemory::Close() {
   shm_.Close();
   shm_ = SharedMemoryHandle();
+  if (shm_.type_ == SharedMemoryHandle::POSIX) {
+    if (readonly_mapped_file_ > 0) {
+      if (IGNORE_EINTR(close(readonly_mapped_file_)) < 0)
+        PLOG(ERROR) << "close";
+      readonly_mapped_file_ = -1;
+    }
+  }
+}
+
+bool SharedMemory::PrepareMapFile(ScopedFILE fp, ScopedFD readonly_fd) {
+  DCHECK(!shm_.IsValid());
+  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;
+    }
+  }
+
+  int 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 {
+      NOTREACHED() << "Call to dup failed, errno=" << errno;
+    }
+  }
+  shm_ = SharedMemoryHandle(mapped_file);
+  readonly_mapped_file_ = readonly_fd.release();
+
+  return true;
 }
 
 bool SharedMemory::ShareToProcessCommon(ProcessHandle process,
                                         SharedMemoryHandle* new_handle,
                                         bool close_self,
                                         ShareMode share_mode) {
-  DCHECK(shm_.IsValid());
+  if (shm_.type_ == SharedMemoryHandle::MACH) {
+    DCHECK(shm_.IsValid());
+
+    bool success = false;
+    switch (share_mode) {
+      case SHARE_CURRENT_MODE:
+        *new_handle = shm_.Duplicate();
+        success = true;
+        break;
+      case SHARE_READONLY:
+        success = MakeMachSharedMemoryHandleReadOnly(new_handle, shm_, memory_);
+        break;
+    }
+
+    if (success)
+      new_handle->SetOwnershipPassesToIPC(true);
+
+    if (close_self) {
+      Unmap();
+      Close();
+    }
+
+    return success;
+  }
 
-  bool success = false;
+  int handle_to_dup = -1;
   switch (share_mode) {
     case SHARE_CURRENT_MODE:
-      *new_handle = shm_.Duplicate();
-      success = true;
+      handle_to_dup = shm_.GetFileDescriptor().fd;
       break;
     case SHARE_READONLY:
-      success = MakeMachSharedMemoryHandleReadOnly(new_handle, shm_, memory_);
+      // We could imagine re-opening the file from /dev/fd, but that can't make
+      // it readonly on Mac: https://codereview.chromium.org/27265002/#msg10
+      CHECK_GE(readonly_mapped_file_, 0);
+      handle_to_dup = readonly_mapped_file_;
       break;
   }
 
-  if (success)
-    new_handle->SetOwnershipPassesToIPC(true);
+  const int new_fd = HANDLE_EINTR(dup(handle_to_dup));
+  if (new_fd < 0) {
+    if (close_self) {
+      Unmap();
+      Close();
+    }
+    DPLOG(ERROR) << "dup() failed.";
+    return false;
+  }
+
+  new_handle->SetFileHandle(new_fd, true);
 
   if (close_self) {
     Unmap();
     Close();
   }
 
-  return success;
+  return true;
 }
 
 }  // namespace base