使用重迭 I/O 的具名管道伺服器
以下是使用重迭作業來服務多個管道用戶端同時連線的單一線程管道伺服器範例。 管道伺服器會建立固定數目的管道實例。 每個管道實例都可以連接到不同的管道用戶端。 當管道用戶端使用其管道實例完成時，伺服器會與用戶端中斷連線，並重複使用管道實例以連線到新的用戶端。 此管道伺服器可以與 具名管道用戶端中所述的管道用戶端搭配使用。
OVERLAPPED結構會指定為管道實例上每個ReadFile、WriteFile和ConnectNamedPipe作業的參數。 雖然此範例顯示不同管道實例上的同時作業，但是它會使用 OVERLAPPED 結構中的事件物件，避免在單一管道實例上同時執行作業。 因為相同的事件物件用於每個實例的讀取、寫入和連接作業，所以無法知道哪個作業完成會導致事件設定為使用相同管道實例同時作業的訊號狀態。
每個管道實例的事件控制碼會儲存在傳遞至 WaitForMultipleObjects 函 式的陣列中。 此函式會等候其中一個事件發出訊號，並傳回導致等候作業完成之事件的陣列索引。 本主題中的範例會使用此陣列索引來擷取包含管道實例資訊的結構。 伺服器會使用 結構的 fPendingIO 成員來追蹤實例上最新的 I/O 作業是否擱置中，這需要呼叫 GetOverlappedResult 函式。 伺服器會使用 結構的 dwState 成員來判斷必須針對管道實例執行的下一個作業。
重迭 的 ReadFile、 WriteFile和 ConnectNamedPipe 作業可以在函式傳回時完成。 否則，如果作業擱置中，指定 之 OVERLAPPED 結構中的事件物件會在函式傳回之前設定為非簽署狀態。 當擱置的作業完成時，系統會將事件物件的狀態設定為已發出訊號。 如果作業在函式傳回之前完成，事件物件的狀態不會變更。
因為此範例使用手動重設事件物件，所以 WaitForMultipleObjects 函式不會將事件物件的狀態變更為非ignalal。 這很重要，因為範例依賴剩餘處於訊號狀態的事件物件，除非有擱置的作業。
如果 ReadFile、 WriteFile或 ConnectNamedPipe 傳回時作業已經完成，則函式的傳回值會指出結果。 針對讀取和寫入作業，也會傳回傳輸的位元組數目。 如果作業仍然擱置中， ReadFile、 WriteFile或 ConnectNamedPipe 函式會傳回零， 而 GetLastError 函式會傳回ERROR_IO_PENDING。 在此情況下，請使用 GetOverlappedResult 函式，在作業完成之後擷取結果。 GetOverlappedResult 只會傳回擱置作業的結果。 它不會報告在傳回重迭 的 ReadFile、 WriteFile或 ConnectNamedPipe 函式之前已完成的作業結果。
在中斷與用戶端的連線之前，您必須等候指出用戶端已完成的訊號。 (排清檔案緩衝區會破壞重迭 I/O 的用途，因為排清作業會在等候用戶端將 pipe 清空時封鎖執行伺服器執行緒。) 在此範例中，嘗試從管道讀取管線關閉控制碼所產生的錯誤。
#include <windows.h>
#include <stdio.h>
#include <tchar.h>
#include <strsafe.h>
#define CONNECTING_STATE 0
#define READING_STATE 1
#define WRITING_STATE 2
#define INSTANCES 4
#define PIPE_TIMEOUT 5000
#define BUFSIZE 4096
typedef struct
{
OVERLAPPED oOverlap;
HANDLE hPipeInst;
TCHAR chRequest[BUFSIZE];
DWORD cbRead;
TCHAR chReply[BUFSIZE];
DWORD cbToWrite;
DWORD dwState;
BOOL fPendingIO;
} PIPEINST, *LPPIPEINST;
VOID DisconnectAndReconnect(DWORD);
BOOL ConnectToNewClient(HANDLE, LPOVERLAPPED);
VOID GetAnswerToRequest(LPPIPEINST);
PIPEINST Pipe[INSTANCES];
HANDLE hEvents[INSTANCES];
int _tmain(VOID)
{
DWORD i, dwWait, cbRet, dwErr;
BOOL fSuccess;
LPCTSTR lpszPipename = TEXT("\\\\.\\pipe\\mynamedpipe");
// The initial loop creates several instances of a named pipe
// along with an event object for each instance. An
// overlapped ConnectNamedPipe operation is started for
// each instance.
for (i = 0; i < INSTANCES; i++)
{
// Create an event object for this instance.
hEvents[i] = CreateEvent(
NULL, // default security attribute
TRUE, // manual-reset event
TRUE, // initial state = signaled
NULL); // unnamed event object
if (hEvents[i] == NULL)
{
printf("CreateEvent failed with %d.\n", GetLastError());
return 0;
}
Pipe[i].oOverlap.hEvent = hEvents[i];
Pipe[i].oOverlap.Offset = 0;
Pipe[i].oOverlap.OffsetHigh = 0;
Pipe[i].hPipeInst = CreateNamedPipe(
lpszPipename, // pipe name
PIPE_ACCESS_DUPLEX | // read/write access
FILE_FLAG_OVERLAPPED, // overlapped mode
PIPE_TYPE_MESSAGE | // message-type pipe
PIPE_READMODE_MESSAGE | // message-read mode
PIPE_WAIT, // blocking mode
INSTANCES, // number of instances
BUFSIZE*sizeof(TCHAR), // output buffer size
BUFSIZE*sizeof(TCHAR), // input buffer size
PIPE_TIMEOUT, // client time-out
NULL); // default security attributes
if (Pipe[i].hPipeInst == INVALID_HANDLE_VALUE)
{
printf("CreateNamedPipe failed with %d.\n", GetLastError());
return 0;
}
// Call the subroutine to connect to the new client
Pipe[i].fPendingIO = ConnectToNewClient(
Pipe[i].hPipeInst,
&Pipe[i].oOverlap);
Pipe[i].dwState = Pipe[i].fPendingIO ?
CONNECTING_STATE : // still connecting
READING_STATE; // ready to read
}
while (1)
{
// Wait for the event object to be signaled, indicating
// completion of an overlapped read, write, or
// connect operation.
dwWait = WaitForMultipleObjects(
INSTANCES, // number of event objects
hEvents, // array of event objects
FALSE, // does not wait for all
INFINITE); // waits indefinitely
// dwWait shows which pipe completed the operation.
i = dwWait - WAIT_OBJECT_0; // determines which pipe
if (i < 0 || i > (INSTANCES - 1))
{
printf("Index out of range.\n");
return 0;
}
// Get the result if the operation was pending.
if (Pipe[i].fPendingIO)
{
fSuccess = GetOverlappedResult(
Pipe[i].hPipeInst, // handle to pipe
&Pipe[i].oOverlap, // OVERLAPPED structure
&cbRet, // bytes transferred
FALSE); // do not wait
switch (Pipe[i].dwState)
{
// Pending connect operation
case CONNECTING_STATE:
if (! fSuccess)
{
printf("Error %d.\n", GetLastError());
return 0;
}
Pipe[i].dwState = READING_STATE;
break;
// Pending read operation
case READING_STATE:
if (! fSuccess || cbRet == 0)
{
DisconnectAndReconnect(i);
continue;
}
Pipe[i].cbRead = cbRet;
Pipe[i].dwState = WRITING_STATE;
break;
// Pending write operation
case WRITING_STATE:
if (! fSuccess || cbRet != Pipe[i].cbToWrite)
{
DisconnectAndReconnect(i);
continue;
}
Pipe[i].dwState = READING_STATE;
break;
default:
{
printf("Invalid pipe state.\n");
return 0;
}
}
}
// The pipe state determines which operation to do next.
switch (Pipe[i].dwState)
{
// READING_STATE:
// The pipe instance is connected to the client
// and is ready to read a request from the client.
case READING_STATE:
fSuccess = ReadFile(
Pipe[i].hPipeInst,
Pipe[i].chRequest,
BUFSIZE*sizeof(TCHAR),
&Pipe[i].cbRead,
&Pipe[i].oOverlap);
// The read operation completed successfully.
if (fSuccess && Pipe[i].cbRead != 0)
{
Pipe[i].fPendingIO = FALSE;
Pipe[i].dwState = WRITING_STATE;
continue;
}
// The read operation is still pending.
dwErr = GetLastError();
if (! fSuccess && (dwErr == ERROR_IO_PENDING))
{
Pipe[i].fPendingIO = TRUE;
continue;
}
// An error occurred; disconnect from the client.
DisconnectAndReconnect(i);
break;
// WRITING_STATE:
// The request was successfully read from the client.
// Get the reply data and write it to the client.
case WRITING_STATE:
GetAnswerToRequest(&Pipe[i]);
fSuccess = WriteFile(
Pipe[i].hPipeInst,
Pipe[i].chReply,
Pipe[i].cbToWrite,
&cbRet,
&Pipe[i].oOverlap);
// The write operation completed successfully.
if (fSuccess && cbRet == Pipe[i].cbToWrite)
{
Pipe[i].fPendingIO = FALSE;
Pipe[i].dwState = READING_STATE;
continue;
}
// The write operation is still pending.
dwErr = GetLastError();
if (! fSuccess && (dwErr == ERROR_IO_PENDING))
{
Pipe[i].fPendingIO = TRUE;
continue;
}
// An error occurred; disconnect from the client.
DisconnectAndReconnect(i);
break;
default:
{
printf("Invalid pipe state.\n");
return 0;
}
}
}
return 0;
}
// DisconnectAndReconnect(DWORD)
// This function is called when an error occurs or when the client
// closes its handle to the pipe. Disconnect from this client, then
// call ConnectNamedPipe to wait for another client to connect.
VOID DisconnectAndReconnect(DWORD i)
{
// Disconnect the pipe instance.
if (! DisconnectNamedPipe(Pipe[i].hPipeInst) )
{
printf("DisconnectNamedPipe failed with %d.\n", GetLastError());
}
// Call a subroutine to connect to the new client.
Pipe[i].fPendingIO = ConnectToNewClient(
Pipe[i].hPipeInst,
&Pipe[i].oOverlap);
Pipe[i].dwState = Pipe[i].fPendingIO ?
CONNECTING_STATE : // still connecting
READING_STATE; // ready to read
}
// ConnectToNewClient(HANDLE, LPOVERLAPPED)
// This function is called to start an overlapped connect operation.
// It returns TRUE if an operation is pending or FALSE if the
// connection has been completed.
BOOL ConnectToNewClient(HANDLE hPipe, LPOVERLAPPED lpo)
{
BOOL fConnected, fPendingIO = FALSE;
// Start an overlapped connection for this pipe instance.
fConnected = ConnectNamedPipe(hPipe, lpo);
// Overlapped ConnectNamedPipe should return zero.
if (fConnected)
{
printf("ConnectNamedPipe failed with %d.\n", GetLastError());
return 0;
}
switch (GetLastError())
{
// The overlapped connection in progress.
case ERROR_IO_PENDING:
fPendingIO = TRUE;
break;
// Client is already connected, so signal an event.
case ERROR_PIPE_CONNECTED:
if (SetEvent(lpo->hEvent))
break;
// If an error occurs during the connect operation...
default:
{
printf("ConnectNamedPipe failed with %d.\n", GetLastError());
return 0;
}
}
return fPendingIO;
}
VOID GetAnswerToRequest(LPPIPEINST pipe)
{
_tprintf( TEXT("[%d] %s\n"), pipe->hPipeInst, pipe->chRequest);
StringCchCopy( pipe->chReply, BUFSIZE, TEXT("Default answer from server") );
pipe->cbToWrite = (lstrlen(pipe->chReply)+1)*sizeof(TCHAR);
}
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