pg_upgrade: fix -j race condition on Windows

Pg_Upgrade cannot write the command string to the log file and then call
system() to write to the same file without causing occasional file-share
errors on Windows.  So instead, write the command string to the log file
after system(), in those cases.
Backpatch to 9.3.

diff --git a/contrib/pg_upgrade/exec.c b/contrib/pg_upgrade/exec.c
index ef123a8eef3e8845b3ece12a5338fae2bbf7ac81..44f6a756be30f6bf71b4cc3468944afce8dec886 100644 (file)
--- a/contrib/pg_upgrade/exec.c
+++ b/contrib/pg_upgrade/exec.c
@@ -37,12 +37,14 @@ static int  win32_check_directory_write_permissions(void);
  * If throw_error is true, this raises a PG_FATAL error and pg_upgrade
  * terminates; otherwise it is just reported as PG_REPORT and exec_prog()
  * returns false.
+ *
+ * The code requires it be called first from the primary thread on Windows.
  */
 bool
 exec_prog(const char *log_file, const char *opt_log_file,
          bool throw_error, const char *fmt,...)
 {
-   int         result;
+   int         result = 0;
    int         written;
 
 #define MAXCMDLEN (2 * MAXPGPATH)
@@ -50,6 +52,14 @@ exec_prog(const char *log_file, const char *opt_log_file,
    FILE       *log;
    va_list     ap;
 
+#ifdef WIN32
+static DWORD       mainThreadId = 0;
+
+   /* We assume we are called from the primary thread first */
+   if (mainThreadId == 0)
+       mainThreadId = GetCurrentThreadId();
+#endif
+
    written = strlcpy(cmd, SYSTEMQUOTE, sizeof(cmd));
    va_start(ap, fmt);
    written += vsnprintf(cmd + written, MAXCMDLEN - written, fmt, ap);
@@ -61,6 +71,22 @@ exec_prog(const char *log_file, const char *opt_log_file,
    if (written >= MAXCMDLEN)
        pg_log(PG_FATAL, "command too long\n");
 
+   pg_log(PG_VERBOSE, "%s\n", cmd);
+
+#ifdef WIN32
+   /*
+    * For some reason, Windows issues a file-in-use error if we write data
+    * to the log file from a non-primary thread just before we create a
+    * subprocess that also writes to the same log file.  One fix is to
+    * sleep for 100ms.  A cleaner fix is to write to the log file _after_
+    * the subprocess has completed, so we do this only when writing from
+    * a non-primary thread.  fflush(), running system() twice, and
+    * pre-creating the file do not see to help.
+    */
+   if (mainThreadId != GetCurrentThreadId())
+       result = system(cmd);
+#endif
+
    log = fopen(log_file, "a");
 
 #ifdef WIN32
@@ -84,11 +110,18 @@ exec_prog(const char *log_file, const char *opt_log_file,
 
    if (log == NULL)
        pg_log(PG_FATAL, "cannot write to log file %s\n", log_file);
+
 #ifdef WIN32
-   fprintf(log, "\n\n");
+   /* Are we printing "command:" before its output? */
+   if (mainThreadId == GetCurrentThreadId())
+       fprintf(log, "\n\n");
 #endif
-   pg_log(PG_VERBOSE, "%s\n", cmd);
    fprintf(log, "command: %s\n", cmd);
+#ifdef WIN32
+   /* Are we printing "command:" after its output? */
+   if (mainThreadId != GetCurrentThreadId())
+       fprintf(log, "\n\n");
+#endif
 
    /*
     * In Windows, we must close the log file at this point so the file is not
@@ -96,7 +129,11 @@ exec_prog(const char *log_file, const char *opt_log_file,
     */
    fclose(log);
 
-   result = system(cmd);
+#ifdef WIN32
+   /* see comment above */
+   if (mainThreadId == GetCurrentThreadId())
+#endif
+       result = system(cmd);
 
    if (result != 0)
    {
@@ -118,7 +155,6 @@ exec_prog(const char *log_file, const char *opt_log_file,
    }
 
 #ifndef WIN32
-
    /*
     * We can't do this on Windows because it will keep the "pg_ctl start"
     * output filename open until the server stops, so we do the \n\n above on