[sgen] Exclusive write on binary protocol file

If we have binary protocol enabled and the debugged executable will spawn a new mono instance, both of the processes will write to the same debug file, because they share the environment variable, producing invalid results. Add a pid sufix if output file exists in order to separately obtain binary protocol outputs from all mono instances.

diff --git a/mono/sgen/sgen-protocol.c b/mono/sgen/sgen-protocol.c
index 0e77588044ccb5e57630f1bcd699bb740ac10c9c..2e59b6359a4b1aea6f4e650998ae1590e4318d50 100644 (file)
--- a/mono/sgen/sgen-protocol.c
+++ b/mono/sgen/sgen-protocol.c
@@ -19,6 +19,7 @@
 #include "sgen-thread-pool.h"
 #include "sgen-client.h"
 #include "mono/utils/mono-membar.h"
+#include "mono/utils/mono-proclib.h"
 
 #include <errno.h>
 #include <string.h>
@@ -73,9 +74,16 @@ free_filename (char *filename)
 }
 
 static void
-binary_protocol_open_file (void)
+binary_protocol_open_file (gboolean assert_on_failure)
 {
        char *filename;
+#ifdef F_SETLK
+       struct flock lock;
+       lock.l_type = F_WRLCK;
+       lock.l_whence = SEEK_SET;
+       lock.l_start = 0;
+       lock.l_len = 0;
+#endif
 
        if (file_size_limit > 0)
                filename = filename_for_index (current_file_index);
@@ -83,12 +91,24 @@ binary_protocol_open_file (void)
                filename = filename_or_prefix;
 
        do {
-               binary_protocol_file = open (filename, O_CREAT|O_WRONLY|O_TRUNC, 0644);
-               if (binary_protocol_file == -1 && errno != EINTR)
-                       break; /* Failed */
+               binary_protocol_file = open (filename, O_CREAT | O_WRONLY, 0644);
+               if (binary_protocol_file == -1) {
+                       if (errno != EINTR)
+                               break; /* Failed */
+#ifdef F_SETLK
+               } else if (fcntl (binary_protocol_file, F_SETLK, &lock) == -1) {
+                       /* The lock for the file is already taken. Fail */
+                       close (binary_protocol_file);
+                       binary_protocol_file = -1;
+                       break;
+#endif
+               } else {
+                       /* We have acquired the lock. Truncate the file */
+                       ftruncate (binary_protocol_file, 0);
+               }
        } while (binary_protocol_file == -1);
 
-       if (binary_protocol_file == -1)
+       if (binary_protocol_file == -1 && assert_on_failure)
                g_error ("sgen binary protocol: failed to open file");
 
        if (file_size_limit > 0)
@@ -100,12 +120,23 @@ void
 binary_protocol_init (const char *filename, long long limit)
 {
 #ifdef HAVE_UNISTD_H
-       filename_or_prefix = (char *)sgen_alloc_internal_dynamic (strlen (filename) + 1, INTERNAL_MEM_BINARY_PROTOCOL, TRUE);
-       strcpy (filename_or_prefix, filename);
-
        file_size_limit = limit;
 
-       binary_protocol_open_file ();
+       /* Original name length + . + pid length in hex + null terminator */
+       filename_or_prefix = g_strdup_printf ("%s", filename);
+       binary_protocol_open_file (FALSE);
+
+       if (binary_protocol_file == -1) {
+               /* Another process owns the file, try adding the pid suffix to the filename */
+               gint32 pid = mono_process_current_pid ();
+               g_free (filename_or_prefix);
+               filename_or_prefix = g_strdup_printf ("%s.%x", filename, pid);
+               binary_protocol_open_file (TRUE);
+       }
+
+       /* If we have a file size limit, we might need to open additional files */
+       if (file_size_limit == 0)
+               g_free (filename_or_prefix);
 
        binary_protocol_header (PROTOCOL_HEADER_CHECK, PROTOCOL_HEADER_VERSION, SIZEOF_VOID_P, G_BYTE_ORDER == G_LITTLE_ENDIAN);
 #else
@@ -220,7 +251,7 @@ binary_protocol_check_file_overflow (void)
        ++current_file_index;
        current_file_size = 0;
 
-       binary_protocol_open_file ();
+       binary_protocol_open_file (TRUE);
 }
 #endif