Reserve the shared memory region during backend startup on Windows, so

that memory allocated by starting third party DLLs doesn't end up
conflicting with it.

Hopefully this solves the long-time issue with "could not reattach
to shared memory" errors on Win32.

Patch from Tsutomu Yamada and me, based on idea from Trevor Talbot.

src/backend/port/win32_shmem.c

@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/port/win32_shmem.c,v 1.11 2009/06/11 14:49:00 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/port/win32_shmem.c,v 1.12 2009/07/24 20:12:42 mha Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -18,6 +18,7 @@
 
 unsigned long UsedShmemSegID = 0;
 void	   *UsedShmemSegAddr = NULL;
+static Size UsedShmemSegSize = 0;
 
 static void pgwin32_SharedMemoryDelete(int status, Datum shmId);
 
@@ -233,6 +234,7 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port)
 
 	/* Save info for possible future use */
 	UsedShmemSegAddr = memAddress;
+	UsedShmemSegSize = size;
 	UsedShmemSegID = (unsigned long) hmap2;
 
 	return hdr;
@@ -257,6 +259,13 @@ PGSharedMemoryReAttach(void)
 	Assert(UsedShmemSegAddr != NULL);
 	Assert(IsUnderPostmaster);
 
+	/*
+	 * Release memory region reservation that was made by the postmaster
+	 */
+	if (VirtualFree(UsedShmemSegAddr, 0, MEM_RELEASE) == 0)
+		elog(FATAL, "failed to release reserved memory region (addr=%p): %lu",
+			 UsedShmemSegAddr, GetLastError());
+
 	hdr = (PGShmemHeader *) MapViewOfFileEx((HANDLE) UsedShmemSegID, FILE_MAP_READ | FILE_MAP_WRITE, 0, 0, 0, UsedShmemSegAddr);
 	if (!hdr)
 		elog(FATAL, "could not reattach to shared memory (key=%d, addr=%p): %lu",
@@ -302,3 +311,53 @@ pgwin32_SharedMemoryDelete(int status, Datum shmId)
 	if (!CloseHandle((HANDLE) DatumGetInt32(shmId)))
 		elog(LOG, "could not close handle to shared memory: %lu", GetLastError());
 }
+
+/*
+ * pgwin32_ReserveSharedMemoryRegion(hChild)
+ *
+ * Reserve the memory region that will be used for shared memory in a child
+ * process. It is called before the child process starts, to make sure the
+ * memory is available.
+ *
+ * Once the child starts, DLLs loading in different order or threads getting
+ * scheduled differently may allocate memory which can conflict with the
+ * address space we need for our shared memory. By reserving the shared
+ * memory region before the child starts, and freeing it only just before we
+ * attempt to get access to the shared memory forces these allocations to
+ * be given different address ranges that don't conflict.
+ *
+ * NOTE! This function executes in the postmaster, and should for this
+ * reason not use elog(FATAL) since that would take down the postmaster.
+ */
+int
+pgwin32_ReserveSharedMemoryRegion(HANDLE hChild)
+{
+	void *address;
+
+	Assert(UsedShmemSegAddr != NULL);
+	Assert(UsedShmemSegSize != 0);
+
+	address = VirtualAllocEx(hChild, UsedShmemSegAddr, UsedShmemSegSize,
+								MEM_RESERVE, PAGE_READWRITE);
+	if (address == NULL) {
+		/* Don't use FATAL since we're running in the postmaster */
+		elog(LOG, "could not reserve shared memory region (addr=%p) for child %lu: %lu",
+			 UsedShmemSegAddr, hChild, GetLastError());
+		return false;
+	}
+	if (address != UsedShmemSegAddr)
+	{
+		/*
+		 * Should never happen - in theory if allocation granularity causes strange
+		 * effects it could, so check just in case.
+		 *
+		 * Don't use FATAL since we're running in the postmaster.
+		 */
+	    elog(LOG, "reserved shared memory region got incorrect address %p, expected %p",
+			 address, UsedShmemSegAddr);
+		VirtualFreeEx(hChild, address, 0, MEM_RELEASE);
+		return false;
+	}
+
+	return true;
+}

src/backend/postmaster/postmaster.c

@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.584 2009/07/08 18:55:35 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.585 2009/07/24 20:12:42 mha Exp $
  *
  * NOTES
  *
@@ -3635,7 +3635,7 @@ internal_forkexec(int argc, char *argv[], Port *port)
 		return -1;				/* log made by save_backend_variables */
 	}
 
-	/* Drop the shared memory that is now inherited to the backend */
+	/* Drop the parameter shared memory that is now inherited to the backend */
 	if (!UnmapViewOfFile(param))
 		elog(LOG, "could not unmap view of backend parameter file: error code %d",
 			 (int) GetLastError());
@@ -3643,6 +3643,25 @@ internal_forkexec(int argc, char *argv[], Port *port)
 		elog(LOG, "could not close handle to backend parameter file: error code %d",
 			 (int) GetLastError());
 
+	/*
+	 * Reserve the memory region used by our main shared memory segment before we
+	 * resume the child process.
+	 */
+	if (!pgwin32_ReserveSharedMemoryRegion(pi.hProcess))
+	{
+		/*
+		 * Failed to reserve the memory, so terminate the newly created
+		 * process and give up.
+		 */
+		if (!TerminateProcess(pi.hProcess, 255))
+			ereport(ERROR,
+					(errmsg_internal("could not terminate process that failed to reserve memory: error code %d",
+									 (int) GetLastError())));
+		CloseHandle(pi.hProcess);
+		CloseHandle(pi.hThread);
+		return -1;			/* logging done made by pgwin32_ReserveSharedMemoryRegion() */
+	}
+
 	/*
 	 * Now that the backend variables are written out, we start the child
 	 * thread so it can start initializing while we set up the rest of the

src/include/port/win32.h

-/* $PostgreSQL: pgsql/src/include/port/win32.h,v 1.88 2009/06/11 14:49:12 momjian Exp $ */
+/* $PostgreSQL: pgsql/src/include/port/win32.h,v 1.89 2009/07/24 20:12:42 mha Exp $ */
 
 #if defined(_MSC_VER) || defined(__BORLANDC__)
 #define WIN32_ONLY_COMPILER
@@ -288,6 +288,9 @@ extern int	pgwin32_is_admin(void);
 extern int	pgwin32_is_service(void);
 #endif
 
+/* in backend/port/win32_shmem.c */
+extern int	pgwin32_ReserveSharedMemoryRegion(HANDLE);
+
 /* in port/win32error.c */
 extern void _dosmaperr(unsigned long);