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Map and unmap the shared memory block before risking VirtualFree.

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The idea here is to get Windows' userspace infrastructure to allocate
whatever space it needs for MapViewOfFileEx() before we release the
locked-down space that we want to map the shared memory block into.

This is a fairly brute-force attempt, and would likely (for example)
fail with large shared memory on 32-bit Windows.  We could perhaps
ameliorate that by mapping only part of the shared memory block in
this way, but for the moment I just want to see if this approach
will fix dory's problem.

Discussion: https://postgr.es/m/25495.1524517820@sss.pgh.pa.us
This commit is contained in:
Tom Lane 2018-04-30 17:07:14 -04:00
parent ce07aff48f
commit 73042b8d13
1 changed files with 23 additions and 3 deletions
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26
src/backend/port/win32_shmem.c
View File

@ -65,7 +65,7 @@ dumpmem(StringInfo buf, const char *reason)
char *addr = 0;
MEMORY_BASIC_INFORMATION mi;
appendStringInfo(buf, "%s memory map:", reason);
appendStringInfo(buf, "%s memory map:\n", reason);
do
{
memset(&mi, 0, sizeof(mi));
@ -73,10 +73,10 @@ dumpmem(StringInfo buf, const char *reason)
{
if (GetLastError() == ERROR_INVALID_PARAMETER)
break;
appendStringInfo(buf, "\nVirtualQuery failed: %lu", GetLastError());
appendStringInfo(buf, "VirtualQuery failed: %lu\n", GetLastError());
break;
}
appendStringInfo(buf, "\n0x%p+0x%p %s (alloc 0x%p) %s",
appendStringInfo(buf, "0x%p+0x%p %s (alloc 0x%p) %s\n",
mi.BaseAddress, (void *) mi.RegionSize,
mi_type(mi.Type), mi.AllocationBase,
mi_state(mi.State));
@ -457,6 +457,22 @@ PGSharedMemoryReAttach(void)
initStringInfo(&buf);
enlargeStringInfo(&buf, 128 * 1024);
dumpmem(&buf, "beginning PGSharedMemoryReAttach");
hdr = (PGShmemHeader *) MapViewOfFileEx(UsedShmemSegID, FILE_MAP_READ | FILE_MAP_WRITE, 0, 0, 0, NULL);
if (hdr)
{
if (!UnmapViewOfFile(hdr))
elog(LOG, "could not unmap temporary view of shared memory: error code %lu",
GetLastError());
}
else
{
/* This isn't fatal, just unpromising ... */
elog(LOG, "could not attach to shared memory (key=%p) at any address: error code %lu",
UsedShmemSegID, GetLastError());
}
dumpmem(&buf, "before VirtualFree");
/*
@ -479,6 +495,10 @@ PGSharedMemoryReAttach(void)
elog(FATAL, "could not reattach to shared memory (key=%p, addr=%p): error code %lu",
UsedShmemSegID, UsedShmemSegAddr, maperr);
}
dumpmem(&buf, "after MapViewOfFileEx");
elog(LOG, "%s", buf.data);
if (hdr != origUsedShmemSegAddr)
elog(FATAL, "reattaching to shared memory returned unexpected address (got %p, expected %p)",
hdr, origUsedShmemSegAddr);