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

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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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54 changes: 51 additions & 3 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 @@ -26,9 +26,6 @@

#include "arrow/ipc/memory.h"
#include "arrow/ipc/test-common.h"
#include "arrow/test-util.h"
#include "arrow/util/buffer.h"
#include "arrow/util/status.h"

namespace arrow {
namespace ipc {
Expand Down Expand Up @@ -67,6 +64,57 @@ 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_ONLY, &rommap));

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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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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Thanks for the good suggestion.


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

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

std::string path = "ipc-invalid-mode-test";
CreateFile(path, buffer_size);

std::shared_ptr<MemoryMappedSource> rommap;
ASSERT_OK(MemoryMappedSource::Open(path, MemorySource::READ_ONLY, &rommap));

ASSERT_RAISES(IOError, rommap->Write(0, buffer.data(), buffer_size));
}

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

Expand Down
22 changes: 15 additions & 7 deletions cpp/src/arrow/ipc/memory.cc
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Expand Up @@ -41,7 +41,7 @@ MemorySource::~MemorySource() {}

class MemoryMappedSource::Impl {
public:
Impl() : file_(nullptr), is_open_(false), data_(nullptr) {}
Impl() : file_(nullptr), is_open_(false), is_writable_(false), data_(nullptr) {}

~Impl() {
if (is_open_) {
Expand All @@ -53,10 +53,12 @@ class MemoryMappedSource::Impl {
Status Open(const std::string& path, MemorySource::AccessMode mode) {
if (is_open_) { return Status::IOError("A file is already open"); }

path_ = path;
int prot_flags = PROT_READ;
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why are you deleting this?

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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.


if (mode == MemorySource::READ_WRITE) {
file_ = fopen(path.c_str(), "r+b");
prot_flags |= PROT_WRITE;
is_writable_ = true;
} else {
file_ = fopen(path.c_str(), "rb");
}
Expand All @@ -73,14 +75,13 @@ 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));
if (data_ == nullptr) {
void* result = mmap(nullptr, size_, prot_flags, MAP_SHARED, fileno(file_), 0);
if (result == MAP_FAILED) {
std::stringstream ss;
ss << "Memory mapping file failed, errno: " << errno;
return Status::IOError(ss.str());
}
data_ = reinterpret_cast<uint8_t*>(result);

return Status::OK();
}
Expand All @@ -89,11 +90,15 @@ class MemoryMappedSource::Impl {

uint8_t* data() { return data_; }

bool writable() { return is_writable_; }

bool opened() { return is_open_; }

private:
std::string path_;
FILE* file_;
int64_t size_;
bool is_open_;
bool is_writable_;

// The memory map
uint8_t* data_;
Expand Down Expand Up @@ -134,6 +139,9 @@ Status MemoryMappedSource::ReadAt(
}

Status MemoryMappedSource::Write(int64_t position, const uint8_t* data, int64_t nbytes) {
if (!impl_->opened() || !impl_->writable()) {
return Status::IOError("Unable to write");
}
if (position < 0 || position >= impl_->size()) {
return Status::Invalid("position is out of bounds");
}
Expand Down