我正在编写一个并行神经网络模拟器，我最近在我的代码中遇到了一个完全让我感到困惑的问题（我认为我只是一个中级C ++程序员，所以也许我错过了一些明显的东西？）,. ..我的代码涉及一个“服务器”和许多客户（工作人员）从中获取工作，并将结果返回给服务器。这是服务器部分：
#include <iostream>
#include <fstream>
#include <arpa/inet.h>
#include <sys/epoll.h>
#include <errno.h>
#include <sys/ioctl.h>
void advanceToNextInputValue(std::ifstream &trainingData, char &nextCharacter)
{
nextCharacter = trainingData.peek();
while(nextCharacter != EOF && !isdigit(nextCharacter))
{
sleep(1);
trainingData.get();
sleep(1);
nextCharacter = trainingData.peek();
}
}
int main()
{
// Create a socket,...
int listenerSocketNum = socket(AF_INET, SOCK_STREAM, 0);
// Name the socket,...
sockaddr_in socketAddress;
socklen_t socketAddressLength = sizeof(socketAddress);
inet_pton(AF_INET, "127.0.0.1", &(socketAddress.sin_addr));
socketAddress.sin_port = htons(9988);
bind(listenerSocketNum, reinterpret_cast<sockaddr*>(&socketAddress), socketAddressLength);
// Create a connection queue for worker processes waiting to connect to this server,...
listen(listenerSocketNum, SOMAXCONN);
int epollInstance = epoll_create(3); // Expected # of file descriptors to monitor
// Allocate a buffer to store epoll events returned from the network layer
epoll_event* networkEvents = new epoll_event[3];
// Add the server listener socket to the list of file descriptors monitored by epoll,...
networkEvents[0].data.fd = -1; // A marker returned with the event for easy identification of which worker process event belongs to
networkEvents[0].events = EPOLLIN | EPOLLET; // epoll-IN- since we only expect incoming data on this socket (ie: connection requests from workers),...
// epoll-ET- indicates an Edge Triggered watch
epoll_ctl(epollInstance, EPOLL_CTL_ADD, listenerSocketNum, &networkEvents[0]);
char nextCharacter = 'A';
std::ifstream trainingData;
// General multi-purpose/multi-use variables,...
long double v;
signed char w;
int x = 0;
int y;
while(1)
{
y = epoll_wait(epollInstance, networkEvents, 3, -1); // the -1 tells epoll_wait to block indefinitely
while(y > 0)
{
if(networkEvents[y-1].data.fd == -1) // We have a notification on the listener socket indicating a request for a new connection (and we expect only one for this testcase),...
{
x = accept(listenerSocketNum,reinterpret_cast<sockaddr*>(&socketAddress), &socketAddressLength);
networkEvents[y-1].data.fd = x; // Here we are just being lazy and re-using networkEvents[y-1] temporarily,...
networkEvents[y-1].events = EPOLLIN | EPOLLET;
// Add the socket for the new worker to the list of file descriptors monitored,...
epoll_ctl(epollInstance, EPOLL_CTL_ADD, x, &networkEvents[y-1]);
trainingData.open("/tmp/trainingData.txt");
}
else if(networkEvents[y-1].data.fd == x) // Worker is waiting to receive datapoints for calibration,...
{
std::cout << "nextCharacter before call to ioctl: " << nextCharacter << std::endl;
ioctl(networkEvents[y-1].data.fd, FIONREAD, &w);
std::cout << "nextCharacter after call to ioctl: " << nextCharacter << std::endl;
recv(networkEvents[y-1].data.fd, &v, sizeof(v), MSG_DONTWAIT); // Retrieve and discard the 'tickle' from worker
if(nextCharacter != EOF)
{
trainingData >> v;
send(networkEvents[y-1].data.fd, &v, sizeof(v), MSG_DONTWAIT);
advanceToNextInputValue(trainingData, nextCharacter);
}
}
y--;
}
}
close(epollInstance);
return 0;
}
这是客户端部分：
#include <arpa/inet.h>
int main()
{
int workerSocket = socket(AF_INET, SOCK_STREAM, 0);
// Name the socket as agreed with the server:
sockaddr_in serverSocketAddress;
serverSocketAddress.sin_family = AF_INET;
serverSocketAddress.sin_port = htons(9988);
inet_pton(AF_INET, "127.0.0.1", &(serverSocketAddress.sin_addr));
// Connect your socket to the server's socket:
connect(workerSocket, reinterpret_cast<sockaddr*>(&serverSocketAddress), sizeof(serverSocketAddress));
long double z;
while(1)
{
send(workerSocket, &z, sizeof(z), MSG_DONTWAIT); // Send a dummy result/tickle to server,...
recv(workerSocket, &z, sizeof(z), MSG_WAITALL);
}
}
我遇到问题的代码部分如下（来自服务器）：
std::cout << "nextCharacter before call to ioctl: " << nextCharacter << std::endl;
ioctl(networkEvents[y-1].data.fd, FIONREAD, &w);
std::cout << "nextCharacter after call to ioctl: " << nextCharacter << std::endl;
在这里（至少在我的系统上），在某些情况下，对ioctl的调用基本上消除了'nextCharacter'的值，我无法弄清楚如何或为什么！
这些是我期望获得的结果：
$ ./server.exe
nextCharacter before call to ioctl: A
nextCharacter after call to ioctl: A
nextCharacter before call to ioctl: 1
nextCharacter after call to ioctl: 1
nextCharacter before call to ioctl: 9
nextCharacter after call to ioctl: 9
nextCharacter before call to ioctl: 2
nextCharacter after call to ioctl: 2
nextCharacter before call to ioctl: 1
nextCharacter after call to ioctl: 1
nextCharacter before call to ioctl: 1
nextCharacter after call to ioctl: 1
nextCharacter before call to ioctl: 1
nextCharacter after call to ioctl: 1
nextCharacter before call to ioctl: 2
nextCharacter after call to ioctl: 2
nextCharacter before call to ioctl: ÿ
nextCharacter after call to ioctl: ÿ
（带有变音符号的小写'y'是文件结尾字符EOF）
这些是我得到的结果（请注意，我们最终会进入无限循环，因为停止条件依赖于nextCharacter的值并且已经消失，因此它永远不会停止）：
$ ./server.exe
nextCharacter before call to ioctl: A
nextCharacter after call to ioctl:
nextCharacter before call to ioctl: 1
nextCharacter after call to ioctl:
nextCharacter before call to ioctl: 9
nextCharacter after call to ioctl:
nextCharacter before call to ioctl: 2
nextCharacter after call to ioctl:
nextCharacter before call to ioctl: 1
nextCharacter after call to ioctl:
nextCharacter before call to ioctl: 1
nextCharacter after call to ioctl:
nextCharacter before call to ioctl: 1
nextCharacter after call to ioctl:
nextCharacter before call to ioctl: 2
nextCharacter after call to ioctl:
nextCharacter before call to ioctl: ÿ
nextCharacter after call to ioctl:
nextCharacter before call to ioctl: ÿ
nextCharacter after call to ioctl:
nextCharacter before call to ioctl: ÿ
nextCharacter after call to ioctl:
.
.
.
如果我注释掉本节中的任何睡眠陈述（在服务器中）：
void advanceToNextInputValue(std::ifstream &trainingData, char &nextCharacter)
{
nextCharacter = trainingData.peek();
while(nextCharacter != EOF && !isdigit(nextCharacter))
{
sleep(1);
trainingData.get();
sleep(1);
nextCharacter = trainingData.peek();
}
}
然后我得到了我期望得到的结果，......
这是我正在使用的makefile：
$ cat Makefile
all: server client
server: server.cpp
g++ server.cpp -o server.exe -ansi -fno-elide-constructors -O3 -pedantic-errors -Wall -Wextra -Winit-self -Wold-style-cast -Woverloaded-virtual -Wuninitialized -Winit-self
client: client.cpp
g++ client.cpp -o client.exe -ansi -fno-elide-constructors -O3 -pedantic-errors -Wall -Wextra -Winit-self -Wold-style-cast -Woverloaded-virtual -Wuninitialized -Winit-self
使用trainingData.txt文件，如下所示：
$ cat trainingData.txt
15616.16993666375,15616.16993666375,9.28693983312753E20,24.99528974548316,16.91935342923897,16.91935342923897,1.386594632397968E6,2.567209162871251
所以我发现了一个新的bug还是我只是愚蠢的？ :)老实说，我不明白为什么用FIONREAD调用ioctl这应该告诉我等待读取的套接字上有多少字节，应该以任何方式影响变量'nextCharacter'的值，...
请注意，这是原始程序的削减版本，仍然能够重现问题（至少在我的系统上），所以请记住，在上面的代码片段中有些事情可能没有意义：）< / p>
特里
答案 0 :(得分：0)
来自man ioctl_list：
FIONREAD int *
也就是说，FIONREAD需要一个指向整数的指针，但是你传递一个指向signed char的指针。
解决方案：改变你的：
signed char w;
到
int w;
否则您将遭受未定义的行为。
您所看到的解释是，编译器可能将w和nextCharacter变量放在内存中，前者的溢出会覆盖后者的值。