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Fixed work with Shared Memory on Windows. #17273

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Fixed work with Shared Memory on Windows. #17273

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f51a238
Fixed work with Shared Memory on Windows.
Dec 26, 2024
eddb03e
Update tsrm_win32.c
CoderAImen Dec 27, 2024
0f57e0c
Update tsrm_win32.c
CoderAImen Dec 27, 2024
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34 changes: 29 additions & 5 deletions TSRM/tsrm_win32.c
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Original file line number Diff line number Diff line change
Expand Up @@ -688,8 +688,21 @@ TSRM_API int shmget(key_t key, size_t size, int flags)
CloseHandle(shm_handle);
return -1;
}
shm->segment = shm_handle;
shm->descriptor = MapViewOfFileEx(shm->segment, FILE_MAP_ALL_ACCESS, 0, 0, 0, NULL);
if (NULL == shm->segment || INVALID_HANDLE_VALUE == shm->segment) {
shm->segment = shm_handle;
shm->created = created;
}
else if (TRUE == created) {
CloseHandle(shm->segment);
shm->segment = shm_handle;
shm->created = TRUE;
}
Comment on lines +695 to +699
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I don't understand what would be special about created. We either use OpenFileMapping() or CreateFileMapping() to get the shm_handle, and it seems to me that we want to close the shm->segment in neither case.

else {
CloseHandle(shm_handle);
}
if(NULL == shm->descriptor){
shm->descriptor = MapViewOfFileEx(shm->segment, FILE_MAP_ALL_ACCESS, 0, 0, 0, NULL);
}

if (NULL != shm->descriptor && created) {
shm->descriptor->shm_perm.key = key;
Expand Down Expand Up @@ -730,6 +743,7 @@ TSRM_API void *shmat(int key, const void *shmaddr, int flags)
shm->descriptor->shm_atime = time(NULL);
shm->descriptor->shm_lpid = getpid();
shm->descriptor->shm_nattch++;
shm->shm_nattch++;

return shm->addr;
}/*}}}*/
Expand All @@ -746,12 +760,22 @@ TSRM_API int shmdt(const void *shmaddr)
shm->descriptor->shm_dtime = time(NULL);
shm->descriptor->shm_lpid = getpid();
shm->descriptor->shm_nattch--;
shm->shm_nattch--;

ret = 0;
if (shm->descriptor->shm_nattch <= 0) {
ret = UnmapViewOfFile(shm->descriptor) ? 0 : -1;
shm->descriptor = NULL;
if (shm->shm_nattch <= 0) {
shm->shm_nattch = 0;
if (NULL != shm->segment && INVALID_HANDLE_VALUE != shm->segment && FALSE == shm->created) {
if(NULL != shm->descriptor){
ret = UnmapViewOfFile(shm->descriptor) ? 0 : -1;
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I still think that we need to UnmapViewOfFile() "unconditionally". From https://learn.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createfilemappinga:

Therefore, to fully close a file mapping object, an application must unmap all mapped views of the file mapping object by calling UnmapViewOfFile and close the file mapping object handle by calling CloseHandle.

If we only unmap when the number of attachments drops to zero, that would not necessarily match the attachments.

}
shm->descriptor = NULL;
CloseHandle(shm->segment);
shm->segment = INVALID_HANDLE_VALUE;
shm->addr = NULL;
}
}

return ret;
}/*}}}*/

Expand Down
2 changes: 2 additions & 0 deletions TSRM/tsrm_win32.h
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Expand Up @@ -51,6 +51,8 @@ typedef struct {
typedef struct {
void *addr;
HANDLE segment;
BOOL created;
int shm_nattch;
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Okay, I see that we need to track the number of attachments for each process/thread, so that we're able to close the file handle per process/thread when we're done with the SHM.

struct shmid_ds *descriptor;
} shm_pair;

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