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Commit73042b8

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Map and unmap the shared memory block before risking VirtualFree.
The idea here is to get Windows' userspace infrastructure to allocatewhatever space it needs for MapViewOfFileEx() before we release thelocked-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 perhapsameliorate that by mapping only part of the shared memory block inthis way, but for the moment I just want to see if this approachwill fix dory's problem.Discussion:https://postgr.es/m/25495.1524517820@sss.pgh.pa.us
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‎src/backend/port/win32_shmem.c

Lines changed: 23 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -65,18 +65,18 @@ dumpmem(StringInfo buf, const char *reason)
6565
char*addr=0;
6666
MEMORY_BASIC_INFORMATIONmi;
6767

68-
appendStringInfo(buf,"%s memory map:",reason);
68+
appendStringInfo(buf,"%s memory map:\n",reason);
6969
do
7070
{
7171
memset(&mi,0,sizeof(mi));
7272
if (!VirtualQuery(addr,&mi,sizeof(mi)))
7373
{
7474
if (GetLastError()==ERROR_INVALID_PARAMETER)
7575
break;
76-
appendStringInfo(buf,"\nVirtualQuery failed: %lu",GetLastError());
76+
appendStringInfo(buf,"VirtualQuery failed: %lu\n",GetLastError());
7777
break;
7878
}
79-
appendStringInfo(buf,"\n0x%p+0x%p %s (alloc 0x%p) %s",
79+
appendStringInfo(buf,"0x%p+0x%p %s (alloc 0x%p) %s\n",
8080
mi.BaseAddress, (void*)mi.RegionSize,
8181
mi_type(mi.Type),mi.AllocationBase,
8282
mi_state(mi.State));
@@ -457,6 +457,22 @@ PGSharedMemoryReAttach(void)
457457
initStringInfo(&buf);
458458
enlargeStringInfo(&buf,128*1024);
459459

460+
dumpmem(&buf,"beginning PGSharedMemoryReAttach");
461+
462+
hdr= (PGShmemHeader*)MapViewOfFileEx(UsedShmemSegID,FILE_MAP_READ |FILE_MAP_WRITE,0,0,0,NULL);
463+
if (hdr)
464+
{
465+
if (!UnmapViewOfFile(hdr))
466+
elog(LOG,"could not unmap temporary view of shared memory: error code %lu",
467+
GetLastError());
468+
}
469+
else
470+
{
471+
/* This isn't fatal, just unpromising ... */
472+
elog(LOG,"could not attach to shared memory (key=%p) at any address: error code %lu",
473+
UsedShmemSegID,GetLastError());
474+
}
475+
460476
dumpmem(&buf,"before VirtualFree");
461477

462478
/*
@@ -479,6 +495,10 @@ PGSharedMemoryReAttach(void)
479495
elog(FATAL,"could not reattach to shared memory (key=%p, addr=%p): error code %lu",
480496
UsedShmemSegID,UsedShmemSegAddr,maperr);
481497
}
498+
499+
dumpmem(&buf,"after MapViewOfFileEx");
500+
elog(LOG,"%s",buf.data);
501+
482502
if (hdr!=origUsedShmemSegAddr)
483503
elog(FATAL,"reattaching to shared memory returned unexpected address (got %p, expected %p)",
484504
hdr,origUsedShmemSegAddr);

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