Avoid atexit(3) when possible, disable prof_final by default.

atexit(3) can deadlock internally during its own initialization if
jemalloc calls atexit() during jemalloc initialization.  Mitigate the
impact by restructuring prof initialization to avoid calling atexit()
unless the registered function will actually dump a final heap profile.

Additionally, disable prof_final by default so that this land mine is
opt-in rather than opt-out.

This resolves #144.

doc/jemalloc.xml.in

@@ -857,8 +857,14 @@ for (i = 0; i < nbins; i++) {
         <option>--enable-stats</option> is specified during configuration, this
         has the potential to cause deadlock for a multi-threaded process that
         exits while one or more threads are executing in the memory allocation
-        functions.  Therefore, this option should only be used with care; it is
+        functions.  Furthermore, <function>atexit<parameter/></function> may
-        primarily intended as a performance tuning aid during application
+        allocate memory during application initialization and then deadlock
+        internally when jemalloc in turn calls
+        <function>atexit<parameter/></function>, so this option is not
+        univerally usable (though the application can register its own
+        <function>atexit<parameter/></function> function with equivalent
+        functionality).  Therefore, this option should only be used with care;
+        it is primarily intended as a performance tuning aid during application
         development.  This option is disabled by default.</para></listitem>
       </varlistentry>
 
@@ -1155,7 +1161,13 @@ malloc_conf = "xmalloc:true";]]></programlisting>
         <filename>&lt;prefix&gt;.&lt;pid&gt;.&lt;seq&gt;.f.heap</filename>,
         where <literal>&lt;prefix&gt;</literal> is controlled by the <link
         linkend="opt.prof_prefix"><mallctl>opt.prof_prefix</mallctl></link>
-        option.  This option is enabled by default.</para></listitem>
+        option.  Note that <function>atexit<parameter/></function> may allocate
+        memory during application initialization and then deadlock internally
+        when jemalloc in turn calls <function>atexit<parameter/></function>, so
+        this option is not univerally usable (though the application can
+        register its own <function>atexit<parameter/></function> function with
+        equivalent functionality).  This option is disabled by
+        default.</para></listitem>
       </varlistentry>
 
       <varlistentry id="opt.prof_leak">

src/prof.c

@@ -20,7 +20,7 @@ bool		opt_prof_thread_active_init = true;
 size_t		opt_lg_prof_sample = LG_PROF_SAMPLE_DEFAULT;
 ssize_t		opt_lg_prof_interval = LG_PROF_INTERVAL_DEFAULT;
 bool		opt_prof_gdump = false;
-bool		opt_prof_final = true;
+bool		opt_prof_final = false;
 bool		opt_prof_leak = false;
 bool		opt_prof_accum = false;
 char		opt_prof_prefix[
@@ -1487,18 +1487,18 @@ prof_fdump(void)
 	char filename[DUMP_FILENAME_BUFSIZE];
 
 	cassert(config_prof);
+	assert(opt_prof_final);
+	assert(opt_prof_prefix[0] != '\0');
 
 	if (!prof_booted)
 		return;
 	tsd = tsd_fetch();
 
-	if (opt_prof_final && opt_prof_prefix[0] != '\0') {
 	malloc_mutex_lock(&prof_dump_seq_mtx);
 	prof_dump_filename(filename, 'f', VSEQ_INVALID);
 	malloc_mutex_unlock(&prof_dump_seq_mtx);
 	prof_dump(tsd, false, filename, opt_prof_leak);
 }
-}
 
 void
 prof_idump(void)
@@ -2023,7 +2023,8 @@ prof_boot2(void)
 		if (malloc_mutex_init(&prof_dump_mtx))
 			return (true);
 
-		if (atexit(prof_fdump) != 0) {
+		if (opt_prof_final && opt_prof_prefix[0] != '\0' &&
+		    atexit(prof_fdump) != 0) {
 			malloc_write("<jemalloc>: Error in atexit()\n");
 			if (opt_abort)
 				abort();

test/unit/prof_active.c

@@ -2,7 +2,7 @@
 
 #ifdef JEMALLOC_PROF
 const char *malloc_conf =
-    "prof:true,prof_thread_active_init:false,lg_prof_sample:0,prof_final:false";
+    "prof:true,prof_thread_active_init:false,lg_prof_sample:0";
 #endif
 
 static void

test/unit/prof_thread_name.c

@@ -1,8 +1,7 @@
 #include "test/jemalloc_test.h"
 
 #ifdef JEMALLOC_PROF
-const char *malloc_conf =
+const char *malloc_conf = "prof:true,prof_active:false";
-    "prof:true,prof_active:false,prof_final:false";
 #endif
 
 static void