我的理解是,这段代码可以将矢量保存在文件中。
using Alloc = boost::interprocess::allocator<int32_t, boost::interprocess::managed_mapped_file::segment_manager>;
using Vec = boost::interprocess::vector<int32_t, Alloc>;
void f() {
boost::interprocess::managed_mapped_file seg(boost::interprocess::open_or_create, "data.dat", 1024);
auto vec = seg.find_or_construct<Vec>("vec")(seg.get_segment_manager());
// ......
}
但是,当向量尝试获取太多字节时,它抛出bad_alloc
异常。
我无法预测需要多少字节,因此当free_memory减少时,我想出了增加文件的大小。但是,有时在增长时会断言失败。这是最小的代码。
using Alloc = allocator<int32_t, managed_mapped_file::segment_manager>;
using Vec = vector<int32_t, Alloc>;
void test(int, int);
int main()
{
test(4096, 4); // Change this value if not reproduced
return 0;
}
void test(int initialBytes, int extraBytes) {
fprintf(stderr, "test(%d, %d)\n", initialBytes, extraBytes);
remove("data.dat");
auto seg = make_unique<managed_mapped_file>(open_or_create, "data.dat", initialBytes);
auto vec = seg->find_or_construct<Vec>("vec")(seg->get_segment_manager());
fprintf(stderr, "vec->capacity=%ld\n", vec->capacity());
fprintf(stderr, "seg.get_free_memory()=%ld\n\n", seg->get_free_memory());
seg = nullptr;
fprintf(stderr, "tag1\n");
boost::interprocess::managed_mapped_file::grow("data.dat", extraBytes);
fprintf(stderr, "tag2\n");
seg = make_unique<managed_mapped_file>(open_only, "data.dat");
fprintf(stderr, "tag3\n");
vec = seg->find<Vec>("vec").first;
fprintf(stderr, "tag4\n");
fprintf(stderr, "vec->capacity=%ld\n", vec->capacity());
fprintf(stderr, "seg.get_free_memory()=%ld\n\n", seg->get_free_memory());
}
更多小
void test(int initialBytes, int extraBytes) {
remove("data.dat");
auto seg = std::make_unique<managed_mapped_file>(open_or_create, "data.dat", initialBytes);
seg = nullptr;
managed_mapped_file::grow("data.dat", extraBytes);
}
问:如何在不假定最大大小的情况下存储弹性矢量?
我误解了grow
-这是静态功能。因此,我修复了代码。仍然未能通过断言。
[我发现断言在4 <= extraBytes && extraBytes < 24
时失败
您可以在下面查看工作示例。该程序创建小内存映射文件,创建矢量容器,然后通过push_back填充矢量。如果无法进行下一个push_back,则将控制转移到catch块。在此块中,关闭文件,调用函数grow,打开内存映射文件,建立向量,并重复push_back。
#include <iostream>
#define BOOST_DATE_TIME_NO_LIB
#include <boost/interprocess/managed_mapped_file.hpp>
#include <boost/interprocess/file_mapping.hpp>
#include <boost/interprocess/containers/vector.hpp>
#include <boost/interprocess/allocators/allocator.hpp>
#include <string>
namespace IP = boost::interprocess;
template <typename T> using MyVectorT = IP::vector < T, IP::allocator<T, IP::managed_mapped_file::segment_manager>>;
int main(int )
{
const char *FileName = "file.bin";
const std::size_t FileSize = 1000;
using MyVector = MyVectorT<size_t>;
try
{
IP::remove_file_on_destroy tmp{ FileName };
IP::managed_mapped_file segment(IP::create_only
, FileName //Mapped file name
, FileSize); //Mapped file initial size
MyVector *myvector = segment.construct<MyVector>("MyVector")(segment.get_segment_manager());
for (size_t i = 0; i < 100000; ++i) //Insert data in the vector
{
bool push_failure = true;
do
{
try
{
myvector->push_back(i);
push_failure = false; //success of push_back
}
catch (const IP::bad_alloc &) //memory mapped file is too small for vector
{
const size_t grow_size = std::max<size_t>(FileSize, 2 * (myvector->size() + 1) * sizeof(MyVector::value_type)); //estimate memory for new vector capacity
std::cout << "segment size = " << segment.get_size() << " Vector capacity = " << myvector->capacity() << " grow_size = " << grow_size;
//free memory mapped file
segment.flush();
segment.~basic_managed_mapped_file();
IP::managed_mapped_file::grow(FileName, grow_size);
new (&segment) IP::managed_mapped_file(IP::open_only, FileName);
std::cout << " -> new segment size = " << segment.get_size() << std::endl;
myvector = segment.find<MyVector>("MyVector").first;
push_failure = true; //try push_back again!!!
}
} while (push_failure);
}
std::cout << "Vector size =" << myvector->size() << "\n";
for (size_t i = 0; i < 100000; ++i)
{
if ((*myvector)[i] != i)
{
std::cout << "vector error!!! i = " << i << " vector[i] = " << (*myvector)[i] << std::endl;
}
}
}
catch (const std::exception &e)
{
std::cout << "Error " << e.what() << std::endl;
}
catch (...)
{
std::cout << "Error";
}
return 0;
}