fork: let child terminate without requiring signal from parent

The quasi-fork child was waiting for an explicit signal from the parent
before terminating. This synchronization step is unnecessary, and
it makes the child hang if the parent terminates for any reason
while the fork operation is in progress.
In that scenario, and consistently with the Posix version, the child
now completes the fork operation and terminates freely when done.

This fixes https://github.com/MSOpenTech/redis/issues/228

src/Win32_Interop/Win32_QFork.cpp

@@ -177,7 +177,6 @@ struct QForkControl {
     HANDLE forkedProcessReady;
     HANDLE operationComplete;
     HANDLE operationFailed;
-    HANDLE terminateForkedProcess;
 
     // global data pointers to be passed to the forked process
     QForkBeginInfo globalData;
@@ -267,8 +266,6 @@ BOOL QForkSlaveInit(HANDLE QForkConrolMemoryMapHandle, DWORD ParentProcessID) {
         g_pQForkControl->operationComplete = dupOperationComplete;
         SmartHandle dupOperationFailed(shParent,sfvMasterQForkControl->operationFailed);
         g_pQForkControl->operationFailed = dupOperationFailed;
-        SmartHandle dupTerminateProcess(shParent,sfvMasterQForkControl->terminateForkedProcess);
-        g_pQForkControl->terminateForkedProcess = dupTerminateProcess;
 
        // create section handle on MM file
        SIZE_T mmSize = g_pQForkControl->availableBlocksInHeap * cAllocationGranularity;
@@ -333,9 +330,6 @@ BOOL QForkSlaveInit(HANDLE QForkConrolMemoryMapHandle, DWORD ParentProcessID) {
         // let parent know we are done
         SetEvent(g_pQForkControl->operationComplete);
 
-        // parent will notify us when to quit
-        WaitForSingleObject(g_pQForkControl->terminateForkedProcess, INFINITE);
-
         g_pQForkControl = NULL;
         return TRUE;
     }
@@ -599,13 +593,6 @@ BOOL QForkMasterInit( __int64 maxheapBytes ) {
                 system_category(),
                 "CreateEvent failed.");
         }
-        g_pQForkControl->terminateForkedProcess = CreateEvent(NULL,TRUE,FALSE,NULL);
-        if (g_pQForkControl->terminateForkedProcess == NULL) {
-            throw std::system_error(
-                GetLastError(),
-                system_category(),
-                "CreateEvent failed.");
-        }
 
         return TRUE;
     }
@@ -791,10 +778,6 @@ BOOL QForkShutdown() {
             CloseHandle(g_pQForkControl->operationFailed);
             g_pQForkControl->operationFailed = NULL;
         }
-        if (g_pQForkControl->terminateForkedProcess != NULL) {
-            CloseHandle(g_pQForkControl->terminateForkedProcess);
-            g_pQForkControl->terminateForkedProcess = NULL;
-        }
         if (g_pQForkControl->heapMemoryMap != NULL) {
             CloseHandle(g_pQForkControl->heapMemoryMap);
             g_pQForkControl->heapMemoryMap = NULL;
@@ -879,12 +862,6 @@ void CreateChildProcess(PROCESS_INFORMATION *pi, char* logfile, DWORD dwCreation
             system_category(),
             "BeginForkOperation: ResetEvent() failed.");
     }
-    if (ResetEvent(g_pQForkControl->terminateForkedProcess) == FALSE) {
-        throw std::system_error(
-            GetLastError(), 
-            system_category(),
-            "BeginForkOperation: ResetEvent() failed.");
-    }
 
     // Launch the "forked" process
     char fileName[MAX_PATH];
@@ -1153,7 +1130,6 @@ void RejoinCOWPages(HANDLE mmHandle, byte* mmStart, size_t mmSize) {
 
 BOOL EndForkOperation(int * pExitCode) {
     try {
-        SetEvent(g_pQForkControl->terminateForkedProcess);
         if( g_hForkedProcess != 0 )
         {
             if (WaitForSingleObject(g_hForkedProcess, cDeadForkWait) == WAIT_TIMEOUT) {
@@ -1191,12 +1167,6 @@ BOOL EndForkOperation(int * pExitCode) {
                 system_category(),
                 "EndForkOperation: ResetEvent() failed.");
         }
-        if (ResetEvent(g_pQForkControl->terminateForkedProcess) == FALSE) {
-            throw std::system_error(
-                GetLastError(), 
-                system_category(),
-                "EndForkOperation: ResetEvent() failed.");
-        }
 
         // move local changes back into memory mapped views for next fork operation
         RejoinCOWPages(