我正在移植构建在ACE Proactor框架之上的应用程序。该应用程序对于VxWorks和Windows都运行良好,但在内核2.6.X.X的Linux(CentOS 5.5,WindRiver Linux 1.4 & 3.0)上使用librt无法实现。Linux中的同步套接字读/写(“全双工”)(特定于aio)
我已经收窄的问题降到一个非常基本的问题: 应用程序开始异步(通过的aio_read)读取套接字上操作,并随后开始异步(通过aio_write)非常相同的插座上书写。由于该协议是从应用程序结束时初始化的,因此读取操作无法实现。 - 当套接字处于阻塞模式时,永远不会写入,协议“挂起”。 - 使用O_NONBLOCK套接字时,写入成功,但读取无限期地返回“EWOULDBLOCK/EAGAIN”错误,永远不会恢复(即使重新启动AIO操作)。
我经历了多个论坛,无法找到一个明确的答案,这是否应该工作(而且我做错了什么事),或者不可能使用Linux AIO。如果我放弃AIO并寻求不同的实现(通过epoll/poll/select等),是否有可能?
附件是一个示例代码来迅速重新产生在非阻塞套接字的问题:
#include <aio.h>
#include <stdio.h>
#include <stdlib.h>
#include <netdb.h>
#include <string.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <assert.h>
#include <errno.h>
#define BUFSIZE (100)
// Global variables
struct aiocb *cblist[2];
int theSocket;
void InitializeAiocbData(struct aiocb* pAiocb, char* pBuffer)
{
bzero((char *)pAiocb, sizeof(struct aiocb));
pAiocb->aio_fildes = theSocket;
pAiocb->aio_nbytes = BUFSIZE;
pAiocb->aio_offset = 0;
pAiocb->aio_buf = pBuffer;
}
void IssueReadOperation(struct aiocb* pAiocb, char* pBuffer)
{
InitializeAiocbData(pAiocb, pBuffer);
int ret = aio_read(pAiocb);
assert (ret >= 0);
}
void IssueWriteOperation(struct aiocb* pAiocb, char* pBuffer)
{
InitializeAiocbData(pAiocb, pBuffer);
int ret = aio_write(pAiocb);
assert (ret >= 0);
}
int main()
{
int ret;
int nPort = 11111;
char* szServer = "10.10.9.123";
// Connect to the remote server
theSocket = socket(AF_INET, SOCK_STREAM, 0);
assert (theSocket >= 0);
struct hostent *pServer;
struct sockaddr_in serv_addr;
pServer = gethostbyname(szServer);
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(nPort);
bcopy((char *)pServer->h_addr, (char *)&serv_addr.sin_addr.s_addr, pServer->h_length);
assert (connect(theSocket, (const sockaddr*)(&serv_addr), sizeof(serv_addr)) >= 0);
// Set the socket to be non-blocking
int oldFlags = fcntl(theSocket, F_GETFL) ;
int newFlags = oldFlags | O_NONBLOCK;
fcntl(theSocket, F_SETFL, newFlags);
printf("Socket flags: before=%o, after=%o\n", oldFlags, newFlags);
// Construct the AIO callbacks array
struct aiocb my_aiocb1, my_aiocb2;
char* pBuffer = new char[BUFSIZE+1];
bzero((char *)cblist, sizeof(cblist));
cblist[0] = &my_aiocb1;
cblist[1] = &my_aiocb2;
// Start the read and write operations on the same socket
IssueReadOperation(&my_aiocb1, pBuffer);
IssueWriteOperation(&my_aiocb2, pBuffer);
// Wait for I/O completion on both operations
int nRound = 1;
printf("\naio_suspend round #%d:\n", nRound++);
ret = aio_suspend(cblist, 2, NULL);
assert (ret == 0);
// Check the error status for the read and write operations
ret = aio_error(&my_aiocb1);
assert (ret == EWOULDBLOCK);
// Get the return code for the read
{
ssize_t retcode = aio_return(&my_aiocb1);
printf("First read operation results: aio_error=%d, aio_return=%d - That's the first EWOULDBLOCK\n", ret, retcode);
}
ret = aio_error(&my_aiocb2);
assert (ret == EINPROGRESS);
printf("Write operation is still \"in progress\"\n");
// Re-issue the read operation
IssueReadOperation(&my_aiocb1, pBuffer);
// Wait for I/O completion on both operations
printf("\naio_suspend round #%d:\n", nRound++);
ret = aio_suspend(cblist, 2, NULL);
assert (ret == 0);
// Check the error status for the read and write operations for the second time
ret = aio_error(&my_aiocb1);
assert (ret == EINPROGRESS);
printf("Second read operation request is suddenly marked as \"in progress\"\n");
ret = aio_error(&my_aiocb2);
assert (ret == 0);
// Get the return code for the write
{
ssize_t retcode = aio_return(&my_aiocb2);
printf("Write operation has completed with results: aio_error=%d, aio_return=%d\n", ret, retcode);
}
// Now try waiting for the read operation to complete - it'll just busy-wait, receiving "EWOULDBLOCK" indefinitely
do
{
printf("\naio_suspend round #%d:\n", nRound++);
ret = aio_suspend(cblist, 1, NULL);
assert (ret == 0);
// Check the error of the read operation and re-issue if needed
ret = aio_error(&my_aiocb1);
if (ret == EWOULDBLOCK)
{
IssueReadOperation(&my_aiocb1, pBuffer);
printf("EWOULDBLOCK again on the read operation!\n");
}
}
while (ret == EWOULDBLOCK);
}
由于提前, Yotam。
请尝试使用`ace-users @ list.isis.vanderbilt.edu`邮件列表:http://www.cs.wustl.edu/~schmidt/ACE-mail.html – 2011-01-06 16:27:21