我正在移植一个基于ACE Proactor框架构建的应用程序。该应用程序在VxWorks和Windows上运行完美,但在Linux(CentOS 5.5、WindRiver Linux 1.4和3.0)内核2.6.X.X上使用librt时无法正常工作。
我已经将问题缩小到一个非常基本的问题: 应用程序在套接字上开始异步(通过aio_read)读取操作,随后在同一套接字上开始异步(通过aio_write)写入操作。由于协议是从应用程序端初始化的,因此尚未完成读取操作。 - 当套接字处于阻塞模式时,写入永远不会被执行,协议“挂起”。 - 当使用O_NONBLOCK套接字时,写入成功,但读取返回“EWOULDBLOCK / EAGAIN”错误,并且永远无法恢复(即使重新启动AIO操作)。
我查看了多个论坛,没有找到明确的答案,无法确定这是否可行(以及我是否做错了什么),或者Linux AIO是否不支持。如果我放弃AIO并寻求不同的实现(通过epoll / poll / select等),是否可能?
附上一个示例代码,可以快速重现非阻塞套接字上的问题:
感谢您的提前帮助,Yotam。
我已经将问题缩小到一个非常基本的问题: 应用程序在套接字上开始异步(通过aio_read)读取操作,随后在同一套接字上开始异步(通过aio_write)写入操作。由于协议是从应用程序端初始化的,因此尚未完成读取操作。 - 当套接字处于阻塞模式时,写入永远不会被执行,协议“挂起”。 - 当使用O_NONBLOCK套接字时,写入成功,但读取返回“EWOULDBLOCK / EAGAIN”错误,并且永远无法恢复(即使重新启动AIO操作)。
我查看了多个论坛,没有找到明确的答案,无法确定这是否可行(以及我是否做错了什么),或者Linux AIO是否不支持。如果我放弃AIO并寻求不同的实现(通过epoll / poll / select等),是否可能?
附上一个示例代码,可以快速重现非阻塞套接字上的问题:
#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);
}
感谢您的提前帮助,Yotam。
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