[Jack-Devel] jack_client_open creates zombie on client

A general hello

We launch jack from a client thread by making use of the autostart
feature within jack_client_open on GNU/linux. Each time the server is
autostarted a zombie is generated on the client process.

We observed this with 1.9.8 and 1.9.9. using

Autostart method                         :  classic

Since we have to restart the server each time we switch the sample rate
we will run out of pids on the long run.

I scanned the sources and saw that the classic double forking does not
wait on the pid of the first child. This is a common forking lapse.

It seems that this bug is present in both versions (jack1 and jack2).
The patch below can be applied to 1.9.9 but it should be trivial to
inject the necessary changes into the more recent versions. This way you
can massage the code the way you like it. You could even examine the
return status of the first child ;)

Regards
Uli

____
[1] jack_autostart_fork_zombie_bug_fix.patch

diff --git
a/basestation/firmware/tools/jackd/posix/JackPosixServerLaunch.cpp
b/basestation/firmware/tools/jackd/posix/JackPosixServerLaunch.cpp
index 9818f71..1874fa0 100644
--- a/basestation/firmware/tools/jackd/posix/JackPosixServerLaunch.cpp
+++ b/basestation/firmware/tools/jackd/posix/JackPosixServerLaunch.cpp
@@ -159,8 +159,14 @@ static void start_server_classic_aux(const char*
server_name)
     fprintf(stderr, "exec of JACK server (command = \"%s\") failed:
%s\n", command, strerror(errno));
 }

+#include <sys/wait.h>
+
+
 static int start_server_classic(const char* server_name)
 {
+    int status;
+    pid_t first_child_pid;
+
     /* The double fork() forces the server to become a child of
      * init, which will always clean up zombie process state on
      * termination. This even works in cases where the server
@@ -170,7 +176,8 @@ static int start_server_classic(const char* server_name)
      * virtual memory tricks, the overhead of the second fork() is
      * probably relatively small.
      */
-    switch (fork()) {
+    first_child_pid = fork();
+    switch (first_child_pid) {
         case 0:                                        /* child process */
             switch (fork()) {
                 case 0:                        /* grandchild process */
@@ -185,6 +192,8 @@ static int start_server_classic(const char* server_name)
             return 1;          /* failed to start server */
     }

+    waitpid(first_child_pid, &status, 0);
+
     /* only the original parent process goes here */
     return 0;                  /* (probably) successful */
 }


-- 
 Uli Franke -- R&D Engineer Dude
 WEISS ENGINEERING LTD.
 Professional Digital and Analog Audio Products
 Florastrasse 42, 8610 Uster Switzerland
 phone: +41 44 940 20 06, fax: +41 44 940 22 14
 email: [hidden] web: http://www.weiss.ch

 "To define recursion we first have to define recursion."
 "What you boot is what you get."

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