debug: add PDC_TRACE_FLUSH env var to toggle aggressive fflush()

pdcurses/debug.c

@@ -31,11 +31,13 @@ debug
 
 **man-end****************************************************************/
 
+#include <stdlib.h>
 #include <string.h>
 #include <sys/types.h>
 #include <time.h>
 
 FILE *pdc_dbfp = NULL;
+static bool want_fflush = FALSE;
 
 void PDC_debug(const char *fmt, ...)
 {
@@ -53,10 +55,25 @@ void PDC_debug(const char *fmt, ...)
     va_start(args, fmt);
     vfprintf(pdc_dbfp, fmt, args);
     va_end(args);
+
+    /* If you are crashing and losing debugging information, enable this
+     * by setting the environment variable PDC_TRACE_FLUSH to 1. This may
+     * impact performance.
+     */
+    if (want_fflush)
+        fflush(pdc_dbfp);
+
+    /* If with PDC_TRACE_FLUSH enabled you are still losing logging in
+     * crashes, you may need to add a platform-dependent mechanism to flush
+     * the OS buffers as well (such as fsync() on POSIX) -- but expect
+     * terrible performance.
+     */
 }
 
 void traceon(void)
 {
+    char *env;
+
     if (pdc_dbfp)
         fclose(pdc_dbfp);
 
@@ -69,6 +86,9 @@ void traceon(void)
         return;
     }
 
+    if ((env = getenv("PDC_TRACE_FLUSH")))
+        want_fflush = atoi(env);
+
     PDC_LOG(("traceon() - called\n"));
 }
 
@@ -81,4 +101,5 @@ void traceoff(void)
 
     fclose(pdc_dbfp);
     pdc_dbfp = NULL;
+    want_fflush = FALSE;
 }