[Libguestfs] [nbdkit PATCH 1/4] errors: Avoid interleaved errors from parallel threads
Since we construct our error/debug messages via multiple calls
to stdio primitives, we are at risk of multiple threads interleaving
their output if they try to output at once. Add a mutex to group
related outputs into an atomic chunk.
Signed-off-by: Eric Blake <eblake(a)redhat.com>
---
src/errors.c | 30 +++++++++++++++++++++++++++++-
1 file changed, 29 insertions(+), 1 deletion(-)
diff --git a/src/errors.c b/src/errors.c
index 5f14315..2fc83ab 100644
--- a/src/errors.c
+++ b/src/errors.c
@@ -1,5 +1,5 @@
/* nbdkit
- * Copyright (C) 2013 Red Hat Inc.
+ * Copyright (C) 2013-2017 Red Hat Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
@@ -38,10 +38,30 @@
#include <stdarg.h>
#include <string.h>
#include <errno.h>
+#include <assert.h>
+#include <pthread.h>
#include "nbdkit-plugin.h"
#include "internal.h"
+/* Used to group piecemeal message construction into atomic output. */
+static pthread_mutex_t errors_lock = PTHREAD_MUTEX_INITIALIZER;
+
+static void
+lock (void)
+{
+ int r = pthread_mutex_lock(&errors_lock);
+ assert(!r);
+}
+
+static void
+unlock (void)
+{
+ int r = pthread_mutex_unlock(&errors_lock);
+ assert(!r);
+}
+
+/* Called with lock taken. */
static void
prologue (const char *type)
{
@@ -69,11 +89,13 @@ nbdkit_vdebug (const char *fs, va_list args)
if (!verbose)
return;
+ lock ();
prologue ("debug");
vfprintf (stderr, fs, args);
fprintf (stderr, "\n");
+ unlock ();
errno = err;
}
@@ -88,6 +110,7 @@ nbdkit_debug (const char *fs, ...)
if (!verbose)
return;
+ lock ();
prologue ("debug");
va_start (args, fs);
@@ -95,6 +118,7 @@ nbdkit_debug (const char *fs, ...)
va_end (args);
fprintf (stderr, "\n");
+ unlock ();
errno = err;
}
@@ -105,11 +129,13 @@ nbdkit_verror (const char *fs, va_list args)
{
int err = errno;
+ lock ();
prologue ("error");
vfprintf (stderr, fs, args);
fprintf (stderr, "\n");
+ unlock ();
errno = err;
}
@@ -121,6 +147,7 @@ nbdkit_error (const char *fs, ...)
va_list args;
int err = errno;
+ lock ();
prologue ("error");
va_start (args, fs);
@@ -128,6 +155,7 @@ nbdkit_error (const char *fs, ...)
va_end (args);
fprintf (stderr, "\n");
+ unlock ();
errno = err;
}
--
2.13.6