我有一个基于网络(TCP-IP)的自定义 IPC 系统。
考虑代码(以及下面的解释):
#include "boost/shared_ptr.hpp"
#include <string>
using namespace std;
class TCommand {
public:
typedef boost::shared_ptr<TCommand> Ptr;
TCommand() {
cout << " Creating TCommand..." << endl;
}
virtual ~TCommand() {
cout << " Destroying TCommand..." << endl;
}
static TCommand * factory(int classID);
virtual void parse(const char *data, int dataSize) = 0;
virtual void print() = 0;
virtual std::string getType() = 0;
};
class TPingCommand : public TCommand {
public:
static const int classID = 1;
int value;
TPingCommand() : TCommand() {
cout << " Creating TPingCommand..." << endl;
}
virtual ~TPingCommand() {
cout << " Destroying TPingCommand..." << endl;
}
virtual void parse(const char *data, int dataSize) {
if (dataSize < 4) throw 1;
this->value = data[0] << 24 | data[1] << 16 | data[2] << 8 | data[3];
}
virtual void print() {
cout << " TPingCommand:" << endl;
cout << " value = " << dec << this->value << " (0x" << hex << this->value << ")" << endl;
}
virtual std::string getType() {
return "TPingCommand";
}
};
class TOtherCommand : public TCommand {
public:
static const int classID = 2;
int value;
char value2;
short int value3;
TOtherCommand() : TCommand() {
cout << " Creating TOtherCommand..." << endl;
}
virtual ~TOtherCommand() {
cout << " Destroying TOtherCommand..." << endl;
}
virtual void parse(const char *data, int dataSize) {
if (dataSize < 7) throw 1;
this->value = data[0] << 24 | data[1] << 16 | data[2] << 8 | data[3];
this->value2 = data[4];
this->value3 = data[5] << 8 | data[6];
}
virtual void print() {
cout << " TOtherCommand:" << endl;
cout << " value = " << dec << this->value << " (0x" << hex << this->value << ")" << endl;
cout << " value2 = " << dec << this->value2 << " (0x" << hex << (int)this->value2 << ")" << endl;
cout << " value3 = " << dec << this->value3 << " (0x" << hex << this->value3 << ")" << endl;
}
virtual std::string getType() {
return "TOtherCommand";
}
};
TCommand * TCommand::factory(int classID) {
cout << " Factory for classID = " << dec << classID << " (0x" << hex << classID << ")" << endl;
switch (classID) {
case TPingCommand::classID: return new TPingCommand(); break;
case TOtherCommand::classID: return new TOtherCommand(); break;
default: throw 1;
}
}
TCommand::Ptr receiveFromNetwork(int test, TCommand::Ptr knownCommand)
{
// Receive command header from network.
// int classID is the command class internal ID.
// int dataSize is the command's body size in bytes.
// For instance:
// int classId = 2;
// int datasize = 7;
int classId = 1;
int dataSize = 4;
char data[10];
if (test == 0) {
cout << " Using test data 0..." << endl;
classId = 1;
dataSize = 4;
data[0] = 0x01; data[1] = 0x02; data[2] = 0x03; data[3] = 0x04;
} else if (test == 1) {
cout << " Using test data 1..." << endl;
classId = 2;
dataSize = 7;
data[0] = 0x11; data[1] = 0x12; data[2] = 0x13; data[3] = 0x14; data[4] = 0x41; data[5] = 0x16; data[6] = 0x17;
}
TCommand::Ptr cmd;
if (knownCommand == 0) {
cout << " No command provided." << endl;
cmd.reset(TCommand::factory(classId));
cout << " Command created from factory: " << cmd->getType() << endl;
} else {
cmd = knownCommand;
cout << " Command provided: " << cmd->getType() << endl;
}
cout << " Parsing data..." << endl;
cmd->parse(data, dataSize);
// The command was identified as TOtherCommand (classID = 2).
// The factory returned a TOtherCommand instance.
// The TOtherCommand's parse method will check the dataSize is suitable (7 bytes are necessary).
// The parse method will unserialize data to their fields.
// This way, the fields would be:
// data = 0x11121314;
// data2 = 0x42; // 'A' as char.
// data3 = 0x1213;
return cmd;
}
void caller() {
// Case 1 (ok):
// I know I'm going to receive a TPingCommand.
cout << "Test case 1:" << endl;
TCommand::Ptr known(new TPingCommand());
TCommand::Ptr cmd1 = receiveFromNetwork(0, known);
cmd1->print();
// Case 2 (problems):
cout << "Test case 2:" << endl;
TCommand::Ptr dummy;
TCommand::Ptr cmd2 = receiveFromNetwork(1, dummy);
cmd2->print();
cout << "Teardown..." << endl;
}
int main() {
caller();
}
receiveFromNetwork 是一种修改过的工厂方法,用于从网络接收命令,但是,在少数情况下,我先验地知道我将接收哪种类型的命令,所以我创建了它的实例并传递给函数(如 knownCommand)。命令类派生自 TCommand 类。knownCommand 由函数返回(它不是必需的,因为您将它作为参数传递,但它对其他情况很有用)。
在所有其他情况下,从网络接收到的前几个字节描述了命令 classID,我使用它在此函数中创建合适的 TCommand 实例。然后从网络数据中解析命令并在函数结束时返回。knownCommand 只是一个虚拟的 TCommand 实例。
当我通过 knownCommand 时,它运行良好。当我将一个虚拟命令作为参数传递时,它会崩溃(据我所知,双倍免费)。
我考虑过对 knownCommand 使用 TCommand 引用,但是,我不能这样做,因为我必须返回一个共享指针,它会导致相同的原始指针由两个不同的共享指针实例(一个来自调用者方法和另一个在 receiveFromNetwork 方法中)。
任何人都知道如何解决这个问题?
这是有问题的场景的部分 valgrind 输出:
==31859== Thread 2:
==31859== Invalid read of size 4
==31859== at 0x805D7B0: boost::detail::sp_counted_impl_p<TVideoGetSourceSizeCommand>::dispose() (checked_delete.hpp:34)
==31859== by 0x407FF42: Server::receiveFromNetwork() (sp_counted_base_gcc_x86.hpp:145)
==31859== by 0x40800AF: Server::serverThread(void*) (Server.cpp:107)
==31859== by 0x434496D: start_thread (pthread_create.c:300)
==31859== by 0x42B398D: clone (clone.S:130)
非常感谢。