C++ TCP 套接字通信 - 连接按预期工作，几秒钟后失败，没有收到新数据，read(） 和 recv(） 块

我使用的是64位Ubuntu 16.04 LTS。就像我说的，我正在尝试与另一台设备建立TCP套接字连接。程序首先从套接字读取数据以初始化last_recorded_data变量(如下图所示，朝向myStartProcedure()的底部(，我知道这完全按预期工作。然后，程序的其余部分启动，由回调驱动。当我UPDATE_BUFFER_MS做一些更小的东西，比如 8 时，它会在几秒钟后失败。这个值的频率是所需的值，但是如果我为了测试目的(例如 500(将其变大，那么它的工作时间会更长一些，但最终也会以同样的方式失败。

失败如下：我尝试从中读取的设备始终每 8 毫秒发送一次数据，在此数据包中，保留前几个字节用于告诉客户端数据包的大小(以字节为单位(。在正常操作期间，接收的字节数和前几个字节描述的大小相等。但是，在read()调用开始阻止之前直接接收的数据包始终比预期大小小 24 字节，但数据包表示发送的数据包仍应为预期大小。下次尝试获取数据时，read()调用会阻止，并在超时时将errno设置为EAGAIN (Resource temporarily unavailable)。

我尝试与Python应用程序与同一设备进行通信，但它没有遇到相同的问题。此外，我在另一台设备上尝试了这个C++应用程序，我看到了相同的行为，所以我认为这是我的问题。我的代码(简化(如下。如果您看到任何明显的错误，请告诉我，谢谢！！

#include <string>
#include <unistd.h>
#include <iostream>
#include <stdio.h>
#include <errno.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define COMM_DOMAIN AF_INET
#define PORT        8008
#define TIMEOUT_SECS  3
#define TIMEOUT_USECS 0
#define UPDATE_BUFFER_MS 8
#define PACKET_SIZE_BYTES_MAX 1200
//
// Global variables
//
// Socket file descriptor
int socket_conn;
// Tracks the timestamp of the last time data was recorded
// The data packet from the TCP connection is sent every UPDATE_BUFFER_MS milliseconds
unsigned long last_process_cycle_timestamp;
// The most recently heard data, cast to a double
double last_recorded_data;
// The number of bytes expected from a full packet
int full_packet_size;
// The minimum number of bytes needed from the packet, as I don't need all of the data
int min_required_packet_size;
// Helper to cast the packet data to a double
union PacketAsFloat
{
unsigned char byte_values[8];
double decimal_value;
};
// Simple struct to package the data read from the socket
struct SimpleDataStruct
{
// Whether or not the struct was properly populated
bool valid;
// Some data that we're interested in right now
double important_data;
//
// Other, irrelevant members removed for simplicity
//
};
// Procedure to read the next data packet
SimpleDataStruct readCurrentData()
{
SimpleDataStruct data;
data.valid = false;
unsigned char socket_data_buffer[PACKET_SIZE_BYTES_MAX] = {0};
int read_status = read(socket_conn, socket_data_buffer, PACKET_SIZE_BYTES_MAX);
if (read_status < min_required_packet_size)
{
return data;
}
//for (int i = 0; i < read_status - 1; i++)
//{
//  std::cout << static_cast<int>(socket_data_buffer[i]) << ", ";
//}
//std::cout << static_cast<int>(socket_data_buffer[read_status - 1]) << std::endl;
PacketAsFloat packet_union;
for (int j = 0; j < 8; j++)
{
packet_union.byte_values[7 - j] = socket_data_buffer[j + 252];
}
data.important_data = packet_union.decimal_value;
data.valid          = true;
return data;
}
// This acts as the main entry point
void myStartProcedure(std::string host)
{
//
// Code to determine the value for full_packet_size and min_required_packet_size (because it can vary) was removed
// Simplified version is below
//
full_packet_size         = some_known_value;
min_required_packet_size = some_other_known_value;
//
// Create socket connection
//
if ((socket_conn = socket(COMM_DOMAIN, SOCK_STREAM, 0)) < 0)
{
std::cout << "socket_conn heard a bad value..." << std::endl;
return;
}
struct sockaddr_in socket_server_address;
memset(&socket_server_address, '0', sizeof(socket_server_address));
socket_server_address.sin_family = COMM_DOMAIN;
socket_server_address.sin_port   = htons(PORT);
// Create and set timeout
struct timeval timeout_chars;
timeout_chars.tv_sec  = TIMEOUT_SECS;
timeout_chars.tv_usec = TIMEOUT_USECS;
setsockopt(socket_conn, SOL_SOCKET, SO_RCVTIMEO, (const char*)&timeout_chars, sizeof(timeout_chars));
if (inet_pton(COMM_DOMAIN, host.c_str(), &socket_server_address.sin_addr) <= 0)
{
std::cout << "Invalid address heard..." << std::endl;
return;
}
if (connect(socket_conn, (struct sockaddr *)&socket_server_address, sizeof(socket_server_address)) < 0)
{
std::cout << "Failed to make connection to " << host << ":" << PORT << std::endl;
return;
}
else
{
std::cout << "Successfully brought up socket connection..." << std::endl;
}
// Sleep for half a second to let the networking setup properly
sleepMilli(500); // A sleep function I defined elsewhere
SimpleDataStruct initial = readCurrentData();
if (initial.valid)
{
last_recorded_data = initial.important_data;
}
else
{
// Error handling
return -1;
}
//
// Start the rest of the program, which is driven by callbacks
//
}
void updateRequestCallback()
{
unsigned long now_ns = currentTime(); // A function I defined elsewhere that gets the current system time in nanoseconds
if (now_ns - last_process_cycle_timestamp >= 1000000 * UPDATE_BUFFER_MS)
{
SimpleDataStruct current_data = readCurrentData();
if (current_data.valid)
{
last_recorded_data = current_data.important_data;
last_process_cycle_timestamp = now_ns;
}
else
{
// Error handling
std::cout << "ERROR setting updated data, SimpleDataStruct was invalid." << std:endl;
return;
}
}
}

编辑 #1

我应该每次都接收一定数量的字节，我希望read()的返回值也返回该值。但是，我刚刚尝试将PACKET_SIZE_BYTES_MAX的值更改为 2048，read()的返回值现在是 2048，此时它应该是设备发回的数据包的大小(不是 2048(。Python 应用程序还将最大值设置为 2048，其返回的数据包大小是正确的/预期的大小......