fix(sysutil): improve the implementation of Sysutil::put_in_backgroun…

…d on macOS (#4640)

Replaces the system() call with posix_spawn() on macOS to preserve
environment variables. This is essential for Debug builds using
DYLD_IMAGE_SUFFIX=_debug to prevent Qt from loading mixed
configurations.

## Tests

Run the iv application in background mode on macOS without the -F flag,
using a Debug configuration. Previously, the system() call did not
inherit the parent environment variables, causing a mix of Debug and
Release versions of Qt to be loaded.

---------

Signed-off-by: Mikael Sundell <[email protected]>

src/include/OpenImageIO/sysutil.h

@@ -74,11 +74,19 @@ getenv(string_view name, string_view defaultval = {});
 OIIO_UTIL_API void
 usleep(unsigned long useconds);
 
-/// Try to put the process into the background so it doesn't continue to
-/// tie up any shell that it was launched from.  The arguments are the
-/// argc/argv that describe the program and its command line arguments.
+/// Puts the process into the background, detaching it from the shell
+/// to prevent it from occupying the terminal or blocking the shell
+/// it was launched from. This allows the process to continue running
+/// independently in the background.
 /// Return true if successful, false if it was unable to do so.
 OIIO_UTIL_API bool
+put_in_background();
+
+/// Obsolete version. The argc, argv parameters are not used. We suggest
+/// switching to the version of `put_in_background()` that takes no
+/// arguments.
+/// DEPRECATED(3.0) old API.
+OIIO_UTIL_API bool
 put_in_background(int argc, char* argv[]);
 
 /// Number of virtual cores available on this platform (including

src/iv/ivmain.cpp

@@ -103,7 +103,7 @@ main(int argc, char* argv[])
     ArgParse ap = getargs(argc, argv);
 
     if (!ap["foreground_mode"].get<int>())
-        Sysutil::put_in_background(argc, argv);
+        Sysutil::put_in_background();
 
     // LG
     //    Q_INIT_RESOURCE(iv);

src/libutil/sysutil.cpp

@@ -34,9 +34,11 @@
 
 #ifdef __APPLE__
 #    include <TargetConditionals.h>
+#    include <crt_externs.h>
 #    include <mach-o/dyld.h>
 #    include <mach/mach_init.h>
 #    include <mach/task.h>
+#    include <spawn.h>
 #    include <sys/ioctl.h>
 #    include <sys/sysctl.h>
 #    include <unistd.h>
@@ -523,46 +525,33 @@ Term::ansi_bgcolor(int r, int g, int b)
     return ret;
 }
 
-
-
 bool
-#ifdef _WIN32
-Sysutil::put_in_background(int, char*[])
-#else
-Sysutil::put_in_background(int argc, char* argv[])
-#endif
+Sysutil::put_in_background()
 {
-    // You would think that this would be sufficient:
-    //   pid_t pid = fork ();
-    //   if (pid < 0)       // Some kind of error, we were unable to background
-    //      return false;
-    //   if (pid == 0)
-    //       return true;   // This is the child process, so continue with life
-    //   // Otherwise, this is the parent process, so terminate
-    //   exit (0);
-    // But it's not.  On OS X, it's not safe to fork() if your app is linked
-    // against certain libraries or frameworks.  So the only thing that I
-    // think is safe is to exec a new process.
-    // Another solution is this:
-    //    daemon (1, 1);
-    // But it suffers from the same problem on OS X, and seems to just be
-    // a wrapper for fork.
-
 #if defined(__linux__) || defined(__GLIBC__)
     // Simplest case:
     // daemon returns 0 if successful, thus return true if successful
     return daemon(1, 1) == 0;
 
 #elif defined(__APPLE__) && TARGET_OS_OSX
-    std::string newcmd = std::string(argv[0]) + " -F";
-    for (int i = 1; i < argc; ++i) {
-        newcmd += " \"";
-        newcmd += argv[i];
-        newcmd += "\"";
+    // On macOS, check if the parent process is launchd (PID 1).
+    // If getppid() == 1, the current process is already detached from the shell
+    // and running in the background. Returning early prevents spawning
+    // another background process, avoiding infinite recursion.
+    if (getppid() == 1) {
+        return true;
     }
-    newcmd += " &";
-    if (system(newcmd.c_str()) != -1)
+    pid_t pid;
+    posix_spawnattr_t attr;
+    posix_spawnattr_init(&attr);
+    posix_spawnattr_setflags(&attr, POSIX_SPAWN_SETSID);
+    char** argv    = *_NSGetArgv();
+    char** environ = *_NSGetEnviron();
+    int status     = posix_spawn(&pid, argv[0], nullptr, &attr, argv, environ);
+    posix_spawnattr_destroy(&attr);
+    if (status == 0)
         exit(0);
+
     return true;
 
 #elif defined(_WIN32)
@@ -575,6 +564,13 @@ Sysutil::put_in_background(int argc, char* argv[])
 }
 
 
+bool
+Sysutil::put_in_background(int argc, char* argv[])
+{
+    return put_in_background();
+}
+
+
 
 unsigned int
 Sysutil::hardware_concurrency()