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ARROW-194: C++: Allow read-only memory mapped source #72

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jihoonson wants to merge 6 commits into from
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ARROW-194: C++: Allow read-only memory mapped source #72

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d8939fa
Allow read-only memory mapped source.
jihoonson May 7, 2016
5559b8d
- Fixed a wrong protection flag in a test
jihoonson May 8, 2016
22e6128
Simplify error check
jihoonson May 8, 2016
63b99c5
Remove unintended whitespace
jihoonson May 8, 2016
b928031
Add missing initialization
jihoonson May 8, 2016
f55dd22
Change the type of protection flag from int8_t to int
jihoonson May 9, 2016
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36 changes: 36 additions & 0 deletions cpp/src/arrow/ipc/ipc-memory-test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -67,6 +67,42 @@ TEST_F(TestMemoryMappedSource, WriteRead) {
}
}

TEST_F(TestMemoryMappedSource, ReadOnly) {
const int64_t buffer_size = 1024;
std::vector<uint8_t> buffer(buffer_size);

test::random_bytes(1024, 0, buffer.data());

const int reps = 5;

std::string path = "ipc-read-only-test";
CreateFile(path, reps * buffer_size);

std::shared_ptr<MemoryMappedSource> rwmmap;
ASSERT_OK(MemoryMappedSource::Open(path, MemorySource::READ_WRITE, &rwmmap));

int64_t position = 0;
for (int i = 0; i < reps; ++i) {
ASSERT_OK(rwmmap->Write(position, buffer.data(), buffer_size));

position += buffer_size;
}
rwmmap->Close();

std::shared_ptr<MemoryMappedSource> rommap;
ASSERT_OK(MemoryMappedSource::Open(path, MemorySource::READ_WRITE, &rommap));
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@emkornfield emkornfield May 7, 2016

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did you mean to open this read only?

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@jihoonson jihoonson May 8, 2016

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Yes. Sorry for my mistake.


position = 0;
std::shared_ptr<Buffer> out_buffer;
for (int i = 0; i < reps; ++i) {
ASSERT_OK(rommap->ReadAt(position, buffer_size, &out_buffer));

ASSERT_EQ(0, memcmp(out_buffer->data(), buffer.data(), buffer_size));
position += buffer_size;
}
rommap->Close();
}
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@emkornfield emkornfield May 7, 2016

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it might be nice to test that writing to a the file opened in read only mode gives an appropriate error status.

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@jihoonson jihoonson May 8, 2016

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Thanks for the good suggestion.


TEST_F(TestMemoryMappedSource, InvalidFile) {
std::string non_existent_path = "invalid-file-name-asfd";

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5 changes: 3 additions & 2 deletions cpp/src/arrow/ipc/memory.cc
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Expand Up @@ -54,9 +54,11 @@ class MemoryMappedSource::Impl {
if (is_open_) { return Status::IOError("A file is already open"); }

path_ = path;
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@emkornfield emkornfield May 9, 2016

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why are you deleting this?

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@jihoonson jihoonson May 9, 2016

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Because this variable is currently not used anywhere. In addition, current implementation expects a file exists in a given path, which in turn means the file is already created in some other parts of the program. So, I think MemoryMappedSource is not responsible for deleting files used for mmap.
In addition, if path is required later, we can add it again easily.

int prot_flag = PROT_READ;

if (mode == MemorySource::READ_WRITE) {
file_ = fopen(path.c_str(), "r+b");
prot_flag |= PROT_WRITE;
} else {
file_ = fopen(path.c_str(), "rb");
}
Expand All @@ -73,9 +75,8 @@ class MemoryMappedSource::Impl {
fseek(file_, 0L, SEEK_SET);
is_open_ = true;

// TODO(wesm): Add read-only version of this
data_ = reinterpret_cast<uint8_t*>(
mmap(nullptr, size_, PROT_READ | PROT_WRITE, MAP_SHARED, fileno(file_), 0));
mmap(nullptr, size_, prot_flag, MAP_SHARED, fileno(file_), 0));
if (data_ == nullptr) {
std::stringstream ss;
ss << "Memory mapping file failed, errno: " << errno;
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