Support for collecting crash dumps on Windows

Add support for collecting "minidump" style crash dumps on
Windows, by setting up an exception handling filter. Crash
dumps will be generated in PGDATA/crashdumps if the directory
is created (the existance of the directory is used as on/off
switch for the generation of the dumps).

Craig Ringer and Magnus Hagander

doc/src/sgml/installation.sgml

@@ -2734,6 +2734,22 @@ cc-1020 cc: ERROR File = pqcomm.c, Line = 427
     under <command>CMD.EXE</command>, as the MSYS console has
     buffering issues.
    </para>
+
+   <sect3>
+    <title>Collecting crash dumps on Windows</title>
+
+    <para>
+     If PostgreSQL on Windows crashes, it has the ability to generate
+     <productname>minidumps</> that can be used to track down the cause
+     for the crash, similar to core dumps on Unix. These dumps can be
+     read using the <productname>Windows Debugger Tools</> or using
+     <productname>Visual Studio</>. To enable the generation of dumps
+     on Windows, create a subdirectory named <filename>crashdumps</filename>
+     inside the cluster data directory. The dumps will then be written
+     into this directory with a unique name based on the identifier of
+     the crashing process and the current time of the crash.
+    </para>
+   </sect3>
   </sect2>
 
   <sect2 id="installation-notes-sco">

src/backend/main/main.c

@@ -81,6 +81,14 @@ main(int argc, char *argv[])
 	 */
 	argv = save_ps_display_args(argc, argv);
 
+	/*
+	 * If supported on the current platform, set up a handler to be called if
+	 * the backend/postmaster crashes with a fatal signal or exception.
+	 */
+#ifdef WIN32
+	pgwin32_install_crashdump_handler();
+#endif
+
 	/*
 	 * Set up locale information from environment.	Note that LC_CTYPE and
 	 * LC_COLLATE will be overridden later from pg_control if we are in an

src/backend/port/win32/Makefile

@@ -12,6 +12,6 @@ subdir = src/backend/port/win32
 top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
-OBJS = timer.o socket.o signal.o security.o mingwcompat.o
+OBJS = timer.o socket.o signal.o security.o mingwcompat.o crashdump.o
 
 include $(top_srcdir)/src/backend/common.mk

src/backend/port/win32/crashdump.c

+/*-------------------------------------------------------------------------
+ *
+ * win32_crashdump.c
+ *         Automatic crash dump creation for PostgreSQL on Windows
+ *
+ * The crashdump feature traps unhandled win32 exceptions produced by the
+ * backend, and tries to produce a Windows MiniDump crash
+ * dump for later debugging and analysis. The machine performing the dump
+ * doesn't need any special debugging tools; the user only needs to send
+ * the dump to somebody who has the same version of PostgreSQL and has debugging
+ * tools.
+ *
+ * crashdump module originally by Craig Ringer <ringerc@ringerc.id.au>
+ *
+ * LIMITATIONS
+ * ===========
+ * This *won't* work in hard OOM situations or stack overflows.
+ *
+ * For those, it'd be necessary to take a much more complicated approach where
+ * the handler switches to a new stack (if it can) and forks a helper process
+ * to debug it self.
+ *
+ * POSSIBLE FUTURE WORK
+ * ====================
+ * For bonus points, the crash dump format permits embedding of user-supplied
+ * data. If there's anything else that should always be supplied with a crash
+ * dump (postgresql.conf? Last few lines of a log file?), it could potentially
+ * be added, though at the cost of a greater chance of the crash dump failing.
+ *
+ *
+ * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/port/win32/crashdump.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+#include <string.h>
+#include <dbghelp.h>
+
+/*
+ * Much of the following code is based on CodeProject and MSDN examples,
+ * particularly
+ * http://www.codeproject.com/KB/debug/postmortemdebug_standalone1.aspx
+ *
+ * Useful MSDN articles:
+ *
+ * http://msdn.microsoft.com/en-us/library/ff805116(v=VS.85).aspx
+ * http://msdn.microsoft.com/en-us/library/ms679294(VS.85).aspx
+ *
+ * Other useful articles on working with minidumps:
+ * http://www.debuginfo.com/articles/effminidumps.html
+ */
+
+typedef BOOL (WINAPI *MINIDUMPWRITEDUMP)(HANDLE hProcess, DWORD dwPid, HANDLE hFile, MINIDUMP_TYPE DumpType,
+									CONST PMINIDUMP_EXCEPTION_INFORMATION ExceptionParam,
+									CONST PMINIDUMP_USER_STREAM_INFORMATION UserStreamParam,
+									CONST PMINIDUMP_CALLBACK_INFORMATION CallbackParam
+									);
+
+
+/*
+ * This function is the exception handler passed to SetUnhandledExceptionFilter.
+ * It's invoked only if there's an unhandled exception. The handler will use
+ * dbghelp.dll to generate a crash dump, then resume the normal unhandled
+ * exception process, which will generally exit with an error message from
+ * the runtime.
+ *
+ * This function is run under the unhandled exception handler, effectively
+ * in a crash context, so it should be careful with memory and avoid using
+ * any PostgreSQL functions.
+ */
+static LONG WINAPI
+crashDumpHandler(struct _EXCEPTION_POINTERS *pExceptionInfo)
+{
+	/*
+	 * We only write crash dumps if the "crashdumps" directory within
+	 * the postgres data directory exists.
+	 */
+	DWORD attribs = GetFileAttributesA("crashdumps");
+	if (attribs != INVALID_FILE_ATTRIBUTES && (attribs & FILE_ATTRIBUTE_DIRECTORY) )
+	{
+		/* 'crashdumps' exists and is a directory. Try to write a dump' */
+		HMODULE hDll = NULL;
+		MINIDUMPWRITEDUMP pDump = NULL;
+		MINIDUMP_TYPE dumpType;
+		char dumpPath[_MAX_PATH];
+		HANDLE selfProcHandle = GetCurrentProcess();
+		DWORD selfPid = GetProcessId(selfProcHandle);
+		HANDLE dumpFile;
+		DWORD systemTicks;
+		struct _MINIDUMP_EXCEPTION_INFORMATION ExInfo;
+
+		ExInfo.ThreadId = GetCurrentThreadId();
+		ExInfo.ExceptionPointers = pExceptionInfo;
+		ExInfo.ClientPointers = FALSE;
+
+		/* Load the dbghelp.dll library and functions */
+		hDll = LoadLibrary("dbghelp.dll");
+		if (hDll == NULL)
+		{
+			write_stderr("could not load dbghelp.dll, cannot write crashdump\n");
+			return EXCEPTION_CONTINUE_SEARCH;
+		}
+
+		pDump = (MINIDUMPWRITEDUMP)GetProcAddress(hDll, "MiniDumpWriteDump");
+
+		if (pDump==NULL)
+		{
+			write_stderr("could not load required functions in dbghelp.dll, cannot write crashdump\n");
+			return EXCEPTION_CONTINUE_SEARCH;
+		}
+
+		/*
+		 * Dump as much as we can, except shared memory, code segments,
+		 * and memory mapped files.
+		 * Exactly what we can dump depends on the version of dbghelp.dll,
+		 * see:
+		 * http://msdn.microsoft.com/en-us/library/ms680519(v=VS.85).aspx
+		 */
+		dumpType = MiniDumpNormal | MiniDumpWithHandleData |
+			MiniDumpWithDataSegs;
+
+		if (GetProcAddress(hDll, "EnumDirTree") != NULL)
+		{
+			/* If this function exists, we have version 5.2 or newer */
+			dumpType |= MiniDumpWithIndirectlyReferencedMemory |
+				MiniDumpWithPrivateReadWriteMemory;
+		}
+		if (GetProcAddress(hDll, "SymFromIndex") != NULL)
+		{
+			/* If this function exists, we have version 6.2 or newer */
+			dumpType |= MiniDumpWithThreadInfo;
+		}
+
+		systemTicks = GetTickCount();
+		snprintf(dumpPath, _MAX_PATH,
+				 "crashdumps\\postgres-pid%0i-%0i.mdmp", selfPid, systemTicks);
+		dumpPath[_MAX_PATH-1] = '\0';
+
+		dumpFile = CreateFile(dumpPath, GENERIC_WRITE, FILE_SHARE_WRITE,
+							  NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL,
+							  NULL);
+		if (dumpFile==INVALID_HANDLE_VALUE)
+		{
+			write_stderr("could not open crash dump file %s for writing: error code %d\n",
+					dumpPath, GetLastError());
+			return EXCEPTION_CONTINUE_SEARCH;
+		}
+
+		if ((*pDump)(selfProcHandle, selfPid, dumpFile, dumpType, &ExInfo,
+					 NULL, NULL))
+			write_stderr("wrote crash dump to %s\n", dumpPath);
+		else
+			write_stderr("could not write crash dump to %s: error code %08x\n",
+					dumpPath, GetLastError());
+
+		CloseHandle(dumpFile);
+	}
+
+	return EXCEPTION_CONTINUE_SEARCH;
+}
+
+
+void
+pgwin32_install_crashdump_handler(void)
+{
+	SetUnhandledExceptionFilter(crashDumpHandler);
+}

src/include/port/win32.h

@@ -303,6 +303,9 @@ extern int	pgwin32_is_service(void);
 /* in backend/port/win32_shmem.c */
 extern int	pgwin32_ReserveSharedMemoryRegion(HANDLE);
 
+/* in backend/port/win32/crashdump.c */
+extern void pgwin32_install_crashdump_handler(void);
+
 /* in port/win32error.c */
 extern void _dosmaperr(unsigned long);