Fix Windows-specific race condition in syslogger. This could've been

[PostgreSQL.git] / src / backend / postmaster / syslogger.c

/*-------------------------------------------------------------------------
 *
 * syslogger.c
 *
 * The system logger (syslogger) is new in Postgres 8.0. It catches all
 * stderr output from the postmaster, backends, and other subprocesses
 * by redirecting to a pipe, and writes it to a set of logfiles.
 * It's possible to have size and age limits for the logfile configured
 * in postgresql.conf. If these limits are reached or passed, the
 * current logfile is closed and a new one is created (rotated).
 * The logfiles are stored in a subdirectory (configurable in
 * postgresql.conf), using an internal naming scheme that mangles
 * creation time and current postmaster pid.
 *
 * Author: Andreas Pflug <pgadmin@pse-consulting.de>
 *
 * Copyright (c) 2004-2009, PostgreSQL Global Development Group
 *
 *
 * IDENTIFICATION
 *        $PostgreSQL$
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <fcntl.h>
#include <signal.h>
#include <time.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/time.h>

#include "lib/stringinfo.h"
#include "libpq/pqsignal.h"
#include "miscadmin.h"
#include "pgtime.h"
#include "postmaster/fork_process.h"
#include "postmaster/postmaster.h"
#include "postmaster/syslogger.h"
#include "storage/ipc.h"
#include "storage/pg_shmem.h"
#include "utils/guc.h"
#include "utils/ps_status.h"
#include "utils/timestamp.h"

/*
 * We really want line-buffered mode for logfile output, but Windows does
 * not have it, and interprets _IOLBF as _IOFBF (bozos).  So use _IONBF
 * instead on Windows.
 */
#ifdef WIN32
#define LBF_MODE        _IONBF
#else
#define LBF_MODE        _IOLBF
#endif

/*
 * We read() into a temp buffer twice as big as a chunk, so that any fragment
 * left after processing can be moved down to the front and we'll still have
 * room to read a full chunk.
 */
#define READ_BUF_SIZE (2 * PIPE_CHUNK_SIZE)


/*
 * GUC parameters.      Logging_collector cannot be changed after postmaster
 * start, but the rest can change at SIGHUP.
 */
bool            Logging_collector = false;
int                     Log_RotationAge = HOURS_PER_DAY * MINS_PER_HOUR;
int                     Log_RotationSize = 10 * 1024;
char       *Log_directory = NULL;
char       *Log_filename = NULL;
bool            Log_truncate_on_rotation = false;

/*
 * Globally visible state (used by elog.c)
 */
bool            am_syslogger = false;

extern bool redirection_done;

/*
 * Private state
 */
static pg_time_t next_rotation_time;
static bool pipe_eof_seen = false;
static FILE *syslogFile = NULL;
static FILE *csvlogFile = NULL;
static char *last_file_name = NULL;
static char *last_csv_file_name = NULL;

/*
 * Buffers for saving partial messages from different backends. We don't expect
 * that there will be very many outstanding at one time, so 20 seems plenty of
 * leeway. If this array gets full we won't lose messages, but we will lose
 * the protocol protection against them being partially written or interleaved.
 *
 * An inactive buffer has pid == 0 and undefined contents of data.
 */
typedef struct
{
        int32           pid;                    /* PID of source process */
        StringInfoData data;            /* accumulated data, as a StringInfo */
} save_buffer;

#define CHUNK_SLOTS 20
static save_buffer saved_chunks[CHUNK_SLOTS];

/* These must be exported for EXEC_BACKEND case ... annoying */
#ifndef WIN32
int                     syslogPipe[2] = {-1, -1};
#else
HANDLE          syslogPipe[2] = {0, 0};
#endif

#ifdef WIN32
static HANDLE threadHandle = 0;
static CRITICAL_SECTION sysfileSection;
#endif

/*
 * Flags set by interrupt handlers for later service in the main loop.
 */
static volatile sig_atomic_t got_SIGHUP = false;
static volatile sig_atomic_t rotation_requested = false;


/* Local subroutines */
#ifdef EXEC_BACKEND
static pid_t syslogger_forkexec(void);
static void syslogger_parseArgs(int argc, char *argv[]);
#endif
static void process_pipe_input(char *logbuffer, int *bytes_in_logbuffer);
static void flush_pipe_input(char *logbuffer, int *bytes_in_logbuffer);
static void open_csvlogfile(void);

#ifdef WIN32
static unsigned int __stdcall pipeThread(void *arg);
#endif
static void logfile_rotate(bool time_based_rotation, int size_rotation_for);
static char *logfile_getname(pg_time_t timestamp, char *suffix);
static void set_next_rotation_time(void);
static void sigHupHandler(SIGNAL_ARGS);
static void sigUsr1Handler(SIGNAL_ARGS);


/*
 * Main entry point for syslogger process
 * argc/argv parameters are valid only in EXEC_BACKEND case.
 */
NON_EXEC_STATIC void
SysLoggerMain(int argc, char *argv[])
{
#ifndef WIN32
        char            logbuffer[READ_BUF_SIZE];
        int                     bytes_in_logbuffer = 0;
#endif
        char       *currentLogDir;
        char       *currentLogFilename;
        int                     currentLogRotationAge;

        IsUnderPostmaster = true;       /* we are a postmaster subprocess now */

        MyProcPid = getpid();           /* reset MyProcPid */

        MyStartTime = time(NULL);       /* set our start time in case we call elog */

#ifdef EXEC_BACKEND
        syslogger_parseArgs(argc, argv);
#endif   /* EXEC_BACKEND */

        am_syslogger = true;

        init_ps_display("logger process", "", "", "");

        /*
         * If we restarted, our stderr is already redirected into our own input
         * pipe.  This is of course pretty useless, not to mention that it
         * interferes with detecting pipe EOF.  Point stderr to /dev/null. This
         * assumes that all interesting messages generated in the syslogger will
         * come through elog.c and will be sent to write_syslogger_file.
         */
        if (redirection_done)
        {
                int                     fd = open(DEVNULL, O_WRONLY, 0);

                /*
                 * The closes might look redundant, but they are not: we want to be
                 * darn sure the pipe gets closed even if the open failed.      We can
                 * survive running with stderr pointing nowhere, but we can't afford
                 * to have extra pipe input descriptors hanging around.
                 */
                close(fileno(stdout));
                close(fileno(stderr));
                dup2(fd, fileno(stdout));
                dup2(fd, fileno(stderr));
                close(fd);
        }

        /*
         * Syslogger's own stderr can't be the syslogPipe, so set it back to text
         * mode if we didn't just close it. (It was set to binary in
         * SubPostmasterMain).
         */
#ifdef WIN32
        else
                _setmode(_fileno(stderr), _O_TEXT);
#endif

        /*
         * Also close our copy of the write end of the pipe.  This is needed to
         * ensure we can detect pipe EOF correctly.  (But note that in the restart
         * case, the postmaster already did this.)
         */
#ifndef WIN32
        if (syslogPipe[1] >= 0)
                close(syslogPipe[1]);
        syslogPipe[1] = -1;
#else
        if (syslogPipe[1])
                CloseHandle(syslogPipe[1]);
        syslogPipe[1] = 0;
#endif

        /*
         * If possible, make this process a group leader, so that the postmaster
         * can signal any child processes too.  (syslogger probably never has any
         * child processes, but for consistency we make all postmaster child
         * processes do this.)
         */
#ifdef HAVE_SETSID
        if (setsid() < 0)
                elog(FATAL, "setsid() failed: %m");
#endif

        /*
         * Properly accept or ignore signals the postmaster might send us
         *
         * Note: we ignore all termination signals, and instead exit only when all
         * upstream processes are gone, to ensure we don't miss any dying gasps of
         * broken backends...
         */

        pqsignal(SIGHUP, sigHupHandler);        /* set flag to read config file */
        pqsignal(SIGINT, SIG_IGN);
        pqsignal(SIGTERM, SIG_IGN);
        pqsignal(SIGQUIT, SIG_IGN);
        pqsignal(SIGALRM, SIG_IGN);
        pqsignal(SIGPIPE, SIG_IGN);
        pqsignal(SIGUSR1, sigUsr1Handler);      /* request log rotation */
        pqsignal(SIGUSR2, SIG_IGN);

        /*
         * Reset some signals that are accepted by postmaster but not here
         */
        pqsignal(SIGCHLD, SIG_DFL);
        pqsignal(SIGTTIN, SIG_DFL);
        pqsignal(SIGTTOU, SIG_DFL);
        pqsignal(SIGCONT, SIG_DFL);
        pqsignal(SIGWINCH, SIG_DFL);

        PG_SETMASK(&UnBlockSig);

#ifdef WIN32
        /* Fire up separate data transfer thread */
        InitializeCriticalSection(&sysfileSection);

        threadHandle = (HANDLE) _beginthreadex(NULL, 0, pipeThread, NULL, 0, NULL);
        if (threadHandle == 0)
                elog(FATAL, "could not create syslogger data transfer thread: %m");
#endif   /* WIN32 */

        /* remember active logfile parameters */
        currentLogDir = pstrdup(Log_directory);
        currentLogFilename = pstrdup(Log_filename);
        currentLogRotationAge = Log_RotationAge;
        /* set next planned rotation time */
        set_next_rotation_time();

        /* main worker loop */
        for (;;)
        {
                bool            time_based_rotation = false;
                int                     size_rotation_for = 0;

#ifndef WIN32
                int                     bytesRead;
                int                     rc;
                fd_set          rfds;
                struct timeval timeout;
#endif

                if (got_SIGHUP)
                {
                        got_SIGHUP = false;
                        ProcessConfigFile(PGC_SIGHUP);

                        /*
                         * Check if the log directory or filename pattern changed in
                         * postgresql.conf. If so, force rotation to make sure we're
                         * writing the logfiles in the right place.
                         */
                        if (strcmp(Log_directory, currentLogDir) != 0)
                        {
                                pfree(currentLogDir);
                                currentLogDir = pstrdup(Log_directory);
                                rotation_requested = true;
                        }
                        if (strcmp(Log_filename, currentLogFilename) != 0)
                        {
                                pfree(currentLogFilename);
                                currentLogFilename = pstrdup(Log_filename);
                                rotation_requested = true;
                        }

                        /*
                         * If rotation time parameter changed, reset next rotation time,
                         * but don't immediately force a rotation.
                         */
                        if (currentLogRotationAge != Log_RotationAge)
                        {
                                currentLogRotationAge = Log_RotationAge;
                                set_next_rotation_time();
                        }
                }

                if (!rotation_requested && Log_RotationAge > 0)
                {
                        /* Do a logfile rotation if it's time */
                        pg_time_t       now = (pg_time_t) time(NULL);

                        if (now >= next_rotation_time)
                                rotation_requested = time_based_rotation = true;
                }

                if (!rotation_requested && Log_RotationSize > 0)
                {
                        /* Do a rotation if file is too big */
                        if (ftell(syslogFile) >= Log_RotationSize * 1024L)
                        {
                                rotation_requested = true;
                                size_rotation_for |= LOG_DESTINATION_STDERR;
                        }
                        if (csvlogFile != NULL &&
                                ftell(csvlogFile) >= Log_RotationSize * 1024L)
                        {
                                rotation_requested = true;
                                size_rotation_for |= LOG_DESTINATION_CSVLOG;
                        }
                }

                if (rotation_requested)
                {
                        /*
                         * Force rotation when both values are zero. It means the request
                         * was sent by pg_rotate_logfile.
                         */
                        if (!time_based_rotation && size_rotation_for == 0)
                                size_rotation_for = LOG_DESTINATION_STDERR | LOG_DESTINATION_CSVLOG;
                        logfile_rotate(time_based_rotation, size_rotation_for);
                }

#ifndef WIN32

                /*
                 * Wait for some data, timing out after 1 second
                 */
                FD_ZERO(&rfds);
                FD_SET(syslogPipe[0], &rfds);
                timeout.tv_sec = 1;
                timeout.tv_usec = 0;

                rc = select(syslogPipe[0] + 1, &rfds, NULL, NULL, &timeout);

                if (rc < 0)
                {
                        if (errno != EINTR)
                                ereport(LOG,
                                                (errcode_for_socket_access(),
                                                 errmsg("select() failed in logger process: %m")));
                }
                else if (rc > 0 && FD_ISSET(syslogPipe[0], &rfds))
                {
                        bytesRead = piperead(syslogPipe[0],
                                                                 logbuffer + bytes_in_logbuffer,
                                                                 sizeof(logbuffer) - bytes_in_logbuffer);
                        if (bytesRead < 0)
                        {
                                if (errno != EINTR)
                                        ereport(LOG,
                                                        (errcode_for_socket_access(),
                                                         errmsg("could not read from logger pipe: %m")));
                        }
                        else if (bytesRead > 0)
                        {
                                bytes_in_logbuffer += bytesRead;
                                process_pipe_input(logbuffer, &bytes_in_logbuffer);
                                continue;
                        }
                        else
                        {
                                /*
                                 * Zero bytes read when select() is saying read-ready means
                                 * EOF on the pipe: that is, there are no longer any processes
                                 * with the pipe write end open.  Therefore, the postmaster
                                 * and all backends are shut down, and we are done.
                                 */
                                pipe_eof_seen = true;

                                /* if there's any data left then force it out now */
                                flush_pipe_input(logbuffer, &bytes_in_logbuffer);
                        }
                }
#else                                                   /* WIN32 */

                /*
                 * On Windows we leave it to a separate thread to transfer data and
                 * detect pipe EOF.  The main thread just wakes up once a second to
                 * check for SIGHUP and rotation conditions.
                 */
                pg_usleep(1000000L);
#endif   /* WIN32 */

                if (pipe_eof_seen)
                {
                        /*
                         * seeing this message on the real stderr is annoying - so we make
                         * it DEBUG1 to suppress in normal use.
                         */
                        ereport(DEBUG1,
                                        (errmsg("logger shutting down")));

                        /*
                         * Normal exit from the syslogger is here.      Note that we
                         * deliberately do not close syslogFile before exiting; this is to
                         * allow for the possibility of elog messages being generated
                         * inside proc_exit.  Regular exit() will take care of flushing
                         * and closing stdio channels.
                         */
                        proc_exit(0);
                }
        }
}

/*
 * Postmaster subroutine to start a syslogger subprocess.
 */
int
SysLogger_Start(void)
{
        pid_t           sysloggerPid;
        char       *filename;

        if (!Logging_collector)
                return 0;

        /*
         * If first time through, create the pipe which will receive stderr
         * output.
         *
         * If the syslogger crashes and needs to be restarted, we continue to use
         * the same pipe (indeed must do so, since extant backends will be writing
         * into that pipe).
         *
         * This means the postmaster must continue to hold the read end of the
         * pipe open, so we can pass it down to the reincarnated syslogger. This
         * is a bit klugy but we have little choice.
         */
#ifndef WIN32
        if (syslogPipe[0] < 0)
        {
                if (pgpipe(syslogPipe) < 0)
                        ereport(FATAL,
                                        (errcode_for_socket_access(),
                                         (errmsg("could not create pipe for syslog: %m"))));
        }
#else
        if (!syslogPipe[0])
        {
                SECURITY_ATTRIBUTES sa;

                memset(&sa, 0, sizeof(SECURITY_ATTRIBUTES));
                sa.nLength = sizeof(SECURITY_ATTRIBUTES);
                sa.bInheritHandle = TRUE;

                if (!CreatePipe(&syslogPipe[0], &syslogPipe[1], &sa, 32768))
                        ereport(FATAL,
                                        (errcode_for_file_access(),
                                         (errmsg("could not create pipe for syslog: %m"))));
        }
#endif

        /*
         * Create log directory if not present; ignore errors
         */
        mkdir(Log_directory, 0700);

        /*
         * The initial logfile is created right in the postmaster, to verify that
         * the Log_directory is writable.
         */
        filename = logfile_getname(time(NULL), NULL);

        syslogFile = fopen(filename, "a");

        if (!syslogFile)
                ereport(FATAL,
                                (errcode_for_file_access(),
                                 (errmsg("could not create log file \"%s\": %m",
                                                 filename))));

        setvbuf(syslogFile, NULL, LBF_MODE, 0);

        pfree(filename);

#ifdef EXEC_BACKEND
        switch ((sysloggerPid = syslogger_forkexec()))
#else
        switch ((sysloggerPid = fork_process()))
#endif
        {
                case -1:
                        ereport(LOG,
                                        (errmsg("could not fork system logger: %m")));
                        return 0;

#ifndef EXEC_BACKEND
                case 0:
                        /* in postmaster child ... */
                        /* Close the postmaster's sockets */
                        ClosePostmasterPorts(true);

                        /* Lose the postmaster's on-exit routines */
                        on_exit_reset();

                        /* Drop our connection to postmaster's shared memory, as well */
                        PGSharedMemoryDetach();

                        /* do the work */
                        SysLoggerMain(0, NULL);
                        break;
#endif

                default:
                        /* success, in postmaster */

                        /* now we redirect stderr, if not done already */
                        if (!redirection_done)
                        {
#ifndef WIN32
                                fflush(stdout);
                                if (dup2(syslogPipe[1], fileno(stdout)) < 0)
                                        ereport(FATAL,
                                                        (errcode_for_file_access(),
                                                         errmsg("could not redirect stdout: %m")));
                                fflush(stderr);
                                if (dup2(syslogPipe[1], fileno(stderr)) < 0)
                                        ereport(FATAL,
                                                        (errcode_for_file_access(),
                                                         errmsg("could not redirect stderr: %m")));
                                /* Now we are done with the write end of the pipe. */
                                close(syslogPipe[1]);
                                syslogPipe[1] = -1;
#else
                                int                     fd;

                                /*
                                 * open the pipe in binary mode and make sure stderr is binary
                                 * after it's been dup'ed into, to avoid disturbing the pipe
                                 * chunking protocol.
                                 */
                                fflush(stderr);
                                fd = _open_osfhandle((long) syslogPipe[1],
                                                                         _O_APPEND | _O_BINARY);
                                if (dup2(fd, _fileno(stderr)) < 0)
                                        ereport(FATAL,
                                                        (errcode_for_file_access(),
                                                         errmsg("could not redirect stderr: %m")));
                                close(fd);
                                _setmode(_fileno(stderr), _O_BINARY);
                                /* Now we are done with the write end of the pipe. */
                                CloseHandle(syslogPipe[1]);
                                syslogPipe[1] = 0;
#endif
                                redirection_done = true;
                        }

                        /* postmaster will never write the file; close it */
                        fclose(syslogFile);
                        syslogFile = NULL;
                        return (int) sysloggerPid;
        }

        /* we should never reach here */
        return 0;
}


#ifdef EXEC_BACKEND

/*
 * syslogger_forkexec() -
 *
 * Format up the arglist for, then fork and exec, a syslogger process
 */
static pid_t
syslogger_forkexec(void)
{
        char       *av[10];
        int                     ac = 0;
        char            filenobuf[32];

        av[ac++] = "postgres";
        av[ac++] = "--forklog";
        av[ac++] = NULL;                        /* filled in by postmaster_forkexec */

        /* static variables (those not passed by write_backend_variables) */
#ifndef WIN32
        if (syslogFile != NULL)
                snprintf(filenobuf, sizeof(filenobuf), "%d",
                                 fileno(syslogFile));
        else
                strcpy(filenobuf, "-1");
#else                                                   /* WIN32 */
        if (syslogFile != NULL)
                snprintf(filenobuf, sizeof(filenobuf), "%ld",
                                 _get_osfhandle(_fileno(syslogFile)));
        else
                strcpy(filenobuf, "0");
#endif   /* WIN32 */
        av[ac++] = filenobuf;

        av[ac] = NULL;
        Assert(ac < lengthof(av));

        return postmaster_forkexec(ac, av);
}

/*
 * syslogger_parseArgs() -
 *
 * Extract data from the arglist for exec'ed syslogger process
 */
static void
syslogger_parseArgs(int argc, char *argv[])
{
        int                     fd;

        Assert(argc == 4);
        argv += 3;

#ifndef WIN32
        fd = atoi(*argv++);
        if (fd != -1)
        {
                syslogFile = fdopen(fd, "a");
                setvbuf(syslogFile, NULL, LBF_MODE, 0);
        }
#else                                                   /* WIN32 */
        fd = atoi(*argv++);
        if (fd != 0)
        {
                fd = _open_osfhandle(fd, _O_APPEND | _O_TEXT);
                if (fd > 0)
                {
                        syslogFile = fdopen(fd, "a");
                        setvbuf(syslogFile, NULL, LBF_MODE, 0);
                }
        }
#endif   /* WIN32 */
}
#endif   /* EXEC_BACKEND */


/* --------------------------------
 *              pipe protocol handling
 * --------------------------------
 */

/*
 * Process data received through the syslogger pipe.
 *
 * This routine interprets the log pipe protocol which sends log messages as
 * (hopefully atomic) chunks - such chunks are detected and reassembled here.
 *
 * The protocol has a header that starts with two nul bytes, then has a 16 bit
 * length, the pid of the sending process, and a flag to indicate if it is
 * the last chunk in a message. Incomplete chunks are saved until we read some
 * more, and non-final chunks are accumulated until we get the final chunk.
 *
 * All of this is to avoid 2 problems:
 * . partial messages being written to logfiles (messes rotation), and
 * . messages from different backends being interleaved (messages garbled).
 *
 * Any non-protocol messages are written out directly. These should only come
 * from non-PostgreSQL sources, however (e.g. third party libraries writing to
 * stderr).
 *
 * logbuffer is the data input buffer, and *bytes_in_logbuffer is the number
 * of bytes present.  On exit, any not-yet-eaten data is left-justified in
 * logbuffer, and *bytes_in_logbuffer is updated.
 */
static void
process_pipe_input(char *logbuffer, int *bytes_in_logbuffer)
{
        char       *cursor = logbuffer;
        int                     count = *bytes_in_logbuffer;
        int                     dest = LOG_DESTINATION_STDERR;

        /* While we have enough for a header, process data... */
        while (count >= (int) sizeof(PipeProtoHeader))
        {
                PipeProtoHeader p;
                int                     chunklen;

                /* Do we have a valid header? */
                memcpy(&p, cursor, sizeof(PipeProtoHeader));
                if (p.nuls[0] == '\0' && p.nuls[1] == '\0' &&
                        p.len > 0 && p.len <= PIPE_MAX_PAYLOAD &&
                        p.pid != 0 &&
                        (p.is_last == 't' || p.is_last == 'f' ||
                         p.is_last == 'T' || p.is_last == 'F'))
                {
                        chunklen = PIPE_HEADER_SIZE + p.len;

                        /* Fall out of loop if we don't have the whole chunk yet */
                        if (count < chunklen)
                                break;

                        dest = (p.is_last == 'T' || p.is_last == 'F') ?
                                LOG_DESTINATION_CSVLOG : LOG_DESTINATION_STDERR;

                        if (p.is_last == 'f' || p.is_last == 'F')
                        {
                                /*
                                 * Save a complete non-final chunk in the per-pid buffer if
                                 * possible - if not just write it out.
                                 */
                                int                     free_slot = -1,
                                                        existing_slot = -1;
                                int                     i;
                                StringInfo      str;

                                for (i = 0; i < CHUNK_SLOTS; i++)
                                {
                                        if (saved_chunks[i].pid == p.pid)
                                        {
                                                existing_slot = i;
                                                break;
                                        }
                                        if (free_slot < 0 && saved_chunks[i].pid == 0)
                                                free_slot = i;
                                }
                                if (existing_slot >= 0)
                                {
                                        str = &(saved_chunks[existing_slot].data);
                                        appendBinaryStringInfo(str,
                                                                                   cursor + PIPE_HEADER_SIZE,
                                                                                   p.len);
                                }
                                else if (free_slot >= 0)
                                {
                                        saved_chunks[free_slot].pid = p.pid;
                                        str = &(saved_chunks[free_slot].data);
                                        initStringInfo(str);
                                        appendBinaryStringInfo(str,
                                                                                   cursor + PIPE_HEADER_SIZE,
                                                                                   p.len);
                                }
                                else
                                {
                                        /*
                                         * If there is no free slot we'll just have to take our
                                         * chances and write out a partial message and hope that
                                         * it's not followed by something from another pid.
                                         */
                                        write_syslogger_file(cursor + PIPE_HEADER_SIZE, p.len,
                                                                                 dest);
                                }
                        }
                        else
                        {
                                /*
                                 * Final chunk --- add it to anything saved for that pid, and
                                 * either way write the whole thing out.
                                 */
                                int                     existing_slot = -1;
                                int                     i;
                                StringInfo      str;

                                for (i = 0; i < CHUNK_SLOTS; i++)
                                {
                                        if (saved_chunks[i].pid == p.pid)
                                        {
                                                existing_slot = i;
                                                break;
                                        }
                                }
                                if (existing_slot >= 0)
                                {
                                        str = &(saved_chunks[existing_slot].data);
                                        appendBinaryStringInfo(str,
                                                                                   cursor + PIPE_HEADER_SIZE,
                                                                                   p.len);
                                        write_syslogger_file(str->data, str->len, dest);
                                        saved_chunks[existing_slot].pid = 0;
                                        pfree(str->data);
                                }
                                else
                                {
                                        /* The whole message was one chunk, evidently. */
                                        write_syslogger_file(cursor + PIPE_HEADER_SIZE, p.len,
                                                                                 dest);
                                }
                        }

                        /* Finished processing this chunk */
                        cursor += chunklen;
                        count -= chunklen;
                }
                else
                {
                        /* Process non-protocol data */

                        /*
                         * Look for the start of a protocol header.  If found, dump data
                         * up to there and repeat the loop.  Otherwise, dump it all and
                         * fall out of the loop.  (Note: we want to dump it all if at all
                         * possible, so as to avoid dividing non-protocol messages across
                         * logfiles.  We expect that in many scenarios, a non-protocol
                         * message will arrive all in one read(), and we want to respect
                         * the read() boundary if possible.)
                         */
                        for (chunklen = 1; chunklen < count; chunklen++)
                        {
                                if (cursor[chunklen] == '\0')
                                        break;
                        }
                        /* fall back on the stderr log as the destination */
                        write_syslogger_file(cursor, chunklen, LOG_DESTINATION_STDERR);
                        cursor += chunklen;
                        count -= chunklen;
                }
        }

        /* We don't have a full chunk, so left-align what remains in the buffer */
        if (count > 0 && cursor != logbuffer)
                memmove(logbuffer, cursor, count);
        *bytes_in_logbuffer = count;
}

/*
 * Force out any buffered data
 *
 * This is currently used only at syslogger shutdown, but could perhaps be
 * useful at other times, so it is careful to leave things in a clean state.
 */
static void
flush_pipe_input(char *logbuffer, int *bytes_in_logbuffer)
{
        int                     i;
        StringInfo      str;

        /* Dump any incomplete protocol messages */
        for (i = 0; i < CHUNK_SLOTS; i++)
        {
                if (saved_chunks[i].pid != 0)
                {
                        str = &(saved_chunks[i].data);
                        write_syslogger_file(str->data, str->len, LOG_DESTINATION_STDERR);
                        saved_chunks[i].pid = 0;
                        pfree(str->data);
                }
        }

        /*
         * Force out any remaining pipe data as-is; we don't bother trying to
         * remove any protocol headers that may exist in it.
         */
        if (*bytes_in_logbuffer > 0)
                write_syslogger_file(logbuffer, *bytes_in_logbuffer,
                                                         LOG_DESTINATION_STDERR);
        *bytes_in_logbuffer = 0;
}


/* --------------------------------
 *              logfile routines
 * --------------------------------
 */

/*
 * Write text to the currently open logfile
 *
 * This is exported so that elog.c can call it when am_syslogger is true.
 * This allows the syslogger process to record elog messages of its own,
 * even though its stderr does not point at the syslog pipe.
 */
void
write_syslogger_file(const char *buffer, int count, int destination)
{
        int                     rc;
        FILE       *logfile;

        if (destination == LOG_DESTINATION_CSVLOG && csvlogFile == NULL)
                open_csvlogfile();

#ifdef WIN32
        EnterCriticalSection(&sysfileSection);
#endif

        logfile = destination == LOG_DESTINATION_CSVLOG ? csvlogFile : syslogFile;
        rc = fwrite(buffer, 1, count, logfile);

#ifdef WIN32
        LeaveCriticalSection(&sysfileSection);
#endif

        /* can't use ereport here because of possible recursion */
        if (rc != count)
                write_stderr("could not write to log file: %s\n", strerror(errno));
}

#ifdef WIN32

/*
 * Worker thread to transfer data from the pipe to the current logfile.
 *
 * We need this because on Windows, WaitForSingleObject does not work on
 * unnamed pipes: it always reports "signaled", so the blocking ReadFile won't
 * allow for SIGHUP; and select is for sockets only.
 */
static unsigned int __stdcall
pipeThread(void *arg)
{
        char            logbuffer[READ_BUF_SIZE];
        int                     bytes_in_logbuffer = 0;

        for (;;)
        {
                DWORD           bytesRead;

                if (!ReadFile(syslogPipe[0],
                                          logbuffer + bytes_in_logbuffer,
                                          sizeof(logbuffer) - bytes_in_logbuffer,
                                          &bytesRead, 0))
                {
                        DWORD           error = GetLastError();

                        if (error == ERROR_HANDLE_EOF ||
                                error == ERROR_BROKEN_PIPE)
                                break;
                        _dosmaperr(error);
                        ereport(LOG,
                                        (errcode_for_file_access(),
                                         errmsg("could not read from logger pipe: %m")));
                }
                else if (bytesRead > 0)
                {
                        bytes_in_logbuffer += bytesRead;
                        process_pipe_input(logbuffer, &bytes_in_logbuffer);
                }
        }

        /* We exit the above loop only upon detecting pipe EOF */
        pipe_eof_seen = true;

        /* if there's any data left then force it out now */
        flush_pipe_input(logbuffer, &bytes_in_logbuffer);

        _endthread();
        return 0;
}
#endif   /* WIN32 */

/*
 * open the csv log file - we do this opportunistically, because
 * we don't know if CSV logging will be wanted.
 */
static void
open_csvlogfile(void)
{
        char       *filename;
        FILE       *fh;

        filename = logfile_getname(time(NULL), ".csv");

        fh = fopen(filename, "a");

        if (!fh)
                ereport(FATAL,
                                (errcode_for_file_access(),
                                 (errmsg("could not create log file \"%s\": %m",
                                                 filename))));

        setvbuf(fh, NULL, LBF_MODE, 0);

#ifdef WIN32
        _setmode(_fileno(fh), _O_TEXT);         /* use CRLF line endings on Windows */
#endif

        csvlogFile = fh;

        pfree(filename);

}

/*
 * perform logfile rotation
 */
static void
logfile_rotate(bool time_based_rotation, int size_rotation_for)
{
        char       *filename;
        char       *csvfilename = NULL;
        FILE       *fh;

        rotation_requested = false;

        /*
         * When doing a time-based rotation, invent the new logfile name based on
         * the planned rotation time, not current time, to avoid "slippage" in the
         * file name when we don't do the rotation immediately.
         */
        if (time_based_rotation)
        {
                filename = logfile_getname(next_rotation_time, NULL);
                if (csvlogFile != NULL)
                        csvfilename = logfile_getname(next_rotation_time, ".csv");
        }
        else
        {
                filename = logfile_getname(time(NULL), NULL);
                if (csvlogFile != NULL)
                        csvfilename = logfile_getname(time(NULL), ".csv");
        }

        /*
         * Decide whether to overwrite or append.  We can overwrite if (a)
         * Log_truncate_on_rotation is set, (b) the rotation was triggered by
         * elapsed time and not something else, and (c) the computed file name is
         * different from what we were previously logging into.
         *
         * Note: during the first rotation after forking off from the postmaster,
         * last_file_name will be NULL.  (We don't bother to set it in the
         * postmaster because it ain't gonna work in the EXEC_BACKEND case.) So we
         * will always append in that situation, even though truncating would
         * usually be safe.
         *
         * For consistency, we treat CSV logs the same even though they aren't
         * opened in the postmaster.
         */
        if (time_based_rotation || (size_rotation_for & LOG_DESTINATION_STDERR))
        {
                if (Log_truncate_on_rotation && time_based_rotation &&
                        last_file_name != NULL &&
                        strcmp(filename, last_file_name) != 0)
                        fh = fopen(filename, "w");
                else
                        fh = fopen(filename, "a");

                if (!fh)
                {
                        int                     saveerrno = errno;

                        ereport(LOG,
                                        (errcode_for_file_access(),
                                         errmsg("could not open new log file \"%s\": %m",
                                                        filename)));

                        /*
                         * ENFILE/EMFILE are not too surprising on a busy system; just
                         * keep using the old file till we manage to get a new one.
                         * Otherwise, assume something's wrong with Log_directory and stop
                         * trying to create files.
                         */
                        if (saveerrno != ENFILE && saveerrno != EMFILE)
                        {
                                ereport(LOG,
                                                (errmsg("disabling automatic rotation (use SIGHUP to reenable)")));
                                Log_RotationAge = 0;
                                Log_RotationSize = 0;
                        }
                        pfree(filename);
                        if (csvfilename)
                                pfree(csvfilename);
                        return;
                }

                setvbuf(fh, NULL, LBF_MODE, 0);

#ifdef WIN32
                _setmode(_fileno(fh), _O_TEXT); /* use CRLF line endings on Windows */
#endif

                /* On Windows, need to interlock against data-transfer thread */
#ifdef WIN32
                EnterCriticalSection(&sysfileSection);
#endif
                fclose(syslogFile);
                syslogFile = fh;
#ifdef WIN32
                LeaveCriticalSection(&sysfileSection);
#endif

                /* instead of pfree'ing filename, remember it for next time */
                if (last_file_name != NULL)
                        pfree(last_file_name);
                last_file_name = filename;
        }

        /* Same as above, but for csv file. */

        if (csvlogFile != NULL &&
                (time_based_rotation || (size_rotation_for & LOG_DESTINATION_CSVLOG)))
        {
                if (Log_truncate_on_rotation && time_based_rotation &&
                        last_csv_file_name != NULL &&
                        strcmp(csvfilename, last_csv_file_name) != 0)
                        fh = fopen(csvfilename, "w");
                else
                        fh = fopen(csvfilename, "a");

                if (!fh)
                {
                        int                     saveerrno = errno;

                        ereport(LOG,
                                        (errcode_for_file_access(),
                                         errmsg("could not open new log file \"%s\": %m",
                                                        csvfilename)));

                        /*
                         * ENFILE/EMFILE are not too surprising on a busy system; just
                         * keep using the old file till we manage to get a new one.
                         * Otherwise, assume something's wrong with Log_directory and stop
                         * trying to create files.
                         */
                        if (saveerrno != ENFILE && saveerrno != EMFILE)
                        {
                                ereport(LOG,
                                                (errmsg("disabling automatic rotation (use SIGHUP to reenable)")));
                                Log_RotationAge = 0;
                                Log_RotationSize = 0;
                        }
                        pfree(csvfilename);
                        return;
                }

                setvbuf(fh, NULL, LBF_MODE, 0);

#ifdef WIN32
                _setmode(_fileno(fh), _O_TEXT); /* use CRLF line endings on Windows */
#endif

                /* On Windows, need to interlock against data-transfer thread */
#ifdef WIN32
                EnterCriticalSection(&sysfileSection);
#endif
                fclose(csvlogFile);
                csvlogFile = fh;
#ifdef WIN32
                LeaveCriticalSection(&sysfileSection);
#endif

                /* instead of pfree'ing filename, remember it for next time */
                if (last_csv_file_name != NULL)
                        pfree(last_csv_file_name);
                last_csv_file_name = csvfilename;
        }

        set_next_rotation_time();
}


/*
 * construct logfile name using timestamp information
 *
 * Result is palloc'd.
 */
static char *
logfile_getname(pg_time_t timestamp, char *suffix)
{
        char       *filename;
        int                     len;

        filename = palloc(MAXPGPATH);

        snprintf(filename, MAXPGPATH, "%s/", Log_directory);

        len = strlen(filename);

        /* treat it as a strftime pattern */
        pg_strftime(filename + len, MAXPGPATH - len, Log_filename,
                pg_localtime(&timestamp, log_timezone));

        if (suffix != NULL)
        {
                len = strlen(filename);
                if (len > 4 && (strcmp(filename + (len - 4), ".log") == 0))
                        len -= 4;
                strncpy(filename + len, suffix, MAXPGPATH - len);
        }

        return filename;
}

/*
 * Determine the next planned rotation time, and store in next_rotation_time.
 */
static void
set_next_rotation_time(void)
{
        pg_time_t       now;
        struct pg_tm *tm;
        int                     rotinterval;

        /* nothing to do if time-based rotation is disabled */
        if (Log_RotationAge <= 0)
                return;

        /*
         * The requirements here are to choose the next time > now that is a
         * "multiple" of the log rotation interval.  "Multiple" can be interpreted
         * fairly loosely.      In this version we align to log_timezone rather than
         * GMT.
         */
        rotinterval = Log_RotationAge * SECS_PER_MINUTE;        /* convert to seconds */
        now = (pg_time_t) time(NULL);
        tm = pg_localtime(&now, log_timezone);
        now += tm->tm_gmtoff;
        now -= now % rotinterval;
        now += rotinterval;
        now -= tm->tm_gmtoff;
        next_rotation_time = now;
}

/* --------------------------------
 *              signal handler routines
 * --------------------------------
 */

/* SIGHUP: set flag to reload config file */
static void
sigHupHandler(SIGNAL_ARGS)
{
        got_SIGHUP = true;
}

/* SIGUSR1: set flag to rotate logfile */
static void
sigUsr1Handler(SIGNAL_ARGS)
{
        rotation_requested = true;
}