1 files changed, 61 insertions, 1 deletions

diff --git a/src/backend/port/win32/shmem.c b/src/backend/port/win32/shmem.c
index c7865bda325..2ba144c9a4a 100644
--- a/src/backend/port/win32/shmem.c
+++ b/src/backend/port/win32/shmem.c
@@ -6,14 +6,17 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/port/win32/shmem.c,v 1.13.2.1 2009/05/04 08:36:42 mha Exp $
+ *	  $PostgreSQL: pgsql/src/backend/port/win32/shmem.c,v 1.13.2.2 2010/07/23 13:53:30 mha Exp $
  *
  *-------------------------------------------------------------------------
  */
 
 #include "postgres.h"
+#include "miscadmin.h"
 
 static DWORD s_segsize = 0;
+extern void *UsedShmemSegAddr;
+extern Size UsedShmemSegSize;
 
 /* Detach from a shared mem area based on its address */
 int
@@ -29,6 +32,13 @@ shmdt(const void *shmaddr)
 void *
 shmat(int memId, void *shmaddr, int flag)
 {
+	/* Release the memory region reserved in the postmaster */
+	if (IsUnderPostmaster)
+	{
+		if (VirtualFree(shmaddr, 0, MEM_RELEASE) == 0)
+			elog(FATAL, "failed to release reserved memory region (addr=%p): %lu",
+				 shmaddr, GetLastError());
+	}
 	/* TODO -- shmat needs to count # attached to shared mem */
 	void	   *lpmem = MapViewOfFileEx((HANDLE) memId,
 										FILE_MAP_WRITE | FILE_MAP_READ,
@@ -128,3 +138,53 @@ shmget(int memKey, int size, int flag)
 
 	return (int) hmap;
 }
+
+/*
+ * 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;
+}