我有2个流程,流程1创建一个boostedmanaged_shared_memory段,流程2打开此段。然后重新启动流程1,并且流程1的开始具有以下内容:
struct vshm_remove
{
vshm_remove()
{
boost::interprocess::shared_memory_object::remove("VMySharedMemory");
}
~vshm_remove()
{
boost::interprocess::shared_memory_object::remove("VMySharedMemory");
}
} vremover;
我知道当进程1开始或结束时,将在我的共享内存上调用remove方法,但是如果进程2没有连接到它,它是否不应该仅将其删除?我使用以下命令将进程2附加到共享内存中,
boost::interprocess::managed_shared_memory *vfsegment;
vfsegment = new boost::interprocess::managed_shared_memory(boost::interprocess::open_only, "VMySharedMemory");
我注意到,无论连接了进程2,共享内存都将被删除。
最佳答案
我认为文档中没有提到如果附加了进程shared_memory_object::remove
将会失败。
请参阅本节以供引用:Removing shared memory。尤其:
这意味着对shared_memory_object::remove("foo")
的调用将尝试删除名为“foo”的共享内存,无论如何。
该函数(source here)的实现反射(reflect)了该行为:
inline bool shared_memory_object::remove(const char *filename)
{
try{
//Make sure a temporary path is created for shared memory
std::string shmfile;
ipcdetail::tmp_filename(filename, shmfile);
return ipcdetail::delete_file(shmfile.c_str());
}
catch(...){
return false;
}
}
根据我发布的生产代码的经验,在不再需要访问共享内存之前,我已经成功而不是调用了
shared_memory_object::remove
。我写了一个非常简单的示例主程序,您可能会觉得有帮助。它会根据运行方式附加,创建或删除共享内存。编译后,请尝试以下步骤:
关于为什么上述第2步在调用
shared_memory_object::remove
之后仍然能够访问数据的原因,请参见Constructing Managed Shared Memory。特别:最有可能的是,因为共享内存对象已映射到进程的地址空间,所以不再直接需要共享内存文件本身。
我意识到这是一个非常人为的示例,但是我认为更具体的做法可能会有所帮助。
#include <cctype> // tolower()
#include <iostream>
#include <string>
#include <unistd.h> // sleep()
#include <boost/interprocess/shared_memory_object.hpp>
#include <boost/interprocess/managed_shared_memory.hpp>
int main(int argc, char *argv[])
{
using std::cerr; using std::cout; using std::endl;
using namespace boost::interprocess;
if (argc == 1) {
cout << "usage: " << argv[0] << " <command>\n 'c' create\n 'r' remove\n 'a' attach" << endl;
return 0;
}
const char * shm_name = "shared_memory_segment";
const char * data_name = "the_answer_to_everything";
switch (tolower(argv[1][0])) {
case 'c':
if (shared_memory_object::remove(shm_name)) { cout << "removed: " << shm_name << endl; }
managed_shared_memory(create_only, shm_name, 1024).construct<int>(data_name)(42);
cout << "created: " << shm_name << "\nadded int \"" << data_name << "\": " << 42 << endl;
break;
case 'r':
cout << (shared_memory_object::remove(shm_name) ? "removed: " : "failed to remove: " ) << shm_name << endl;
break;
case 'a':
{
managed_shared_memory segment(open_only, shm_name);
while (true) {
std::pair<int *, std::size_t> data = segment.find<int>( data_name );
if (!data.first || data.second == 0) {
cerr << "Allocation " << data_name << " either not found or empty" << endl;
break;
}
cout << "opened: " << shm_name << " (" << segment.get_segment_manager()->get_size()
<< " bytes)\nretrieved int \"" << data_name << "\": " << *data.first << endl;
sleep(10);
}
}
break;
default:
cerr << "unknown command" << endl;
break;
}
return 0;
}
关于c++ - 附加进程后, boost 删除managed_shared_memory,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/18130781/