Add support for executing a detached process

Author: cpsughrue

llvm/include/llvm/Support/Program.h

@@ -152,7 +152,8 @@ namespace sys {
                             unsigned MemoryLimit = 0,
                             std::string *ErrMsg = nullptr,
                             bool *ExecutionFailed = nullptr,
-                            BitVector *AffinityMask = nullptr);
+                            BitVector *AffinityMask = nullptr,
+                            bool DetachProcess = false);
 
   /// Return true if the given arguments fit within system-specific
   /// argument length limits.

llvm/lib/Support/Program.cpp

@@ -27,7 +27,7 @@ static bool Execute(ProcessInfo &PI, StringRef Program,
                     std::optional<ArrayRef<StringRef>> Env,
                     ArrayRef<std::optional<StringRef>> Redirects,
                     unsigned MemoryLimit, std::string *ErrMsg,
-                    BitVector *AffinityMask);
+                    BitVector *AffinityMask, bool DetachProcess);
 
 int sys::ExecuteAndWait(StringRef Program, ArrayRef<StringRef> Args,
                         std::optional<ArrayRef<StringRef>> Env,
@@ -39,7 +39,7 @@ int sys::ExecuteAndWait(StringRef Program, ArrayRef<StringRef> Args,
   assert(Redirects.empty() || Redirects.size() == 3);
   ProcessInfo PI;
   if (Execute(PI, Program, Args, Env, Redirects, MemoryLimit, ErrMsg,
-              AffinityMask)) {
+              AffinityMask, /*DetachProcess*/ false)) {
     if (ExecutionFailed)
       *ExecutionFailed = false;
     ProcessInfo Result = Wait(
@@ -58,13 +58,14 @@ ProcessInfo sys::ExecuteNoWait(StringRef Program, ArrayRef<StringRef> Args,
                                std::optional<ArrayRef<StringRef>> Env,
                                ArrayRef<std::optional<StringRef>> Redirects,
                                unsigned MemoryLimit, std::string *ErrMsg,
-                               bool *ExecutionFailed, BitVector *AffinityMask) {
+                               bool *ExecutionFailed, BitVector *AffinityMask,
+                               bool DetachProcess) {
   assert(Redirects.empty() || Redirects.size() == 3);
   ProcessInfo PI;
   if (ExecutionFailed)
     *ExecutionFailed = false;
   if (!Execute(PI, Program, Args, Env, Redirects, MemoryLimit, ErrMsg,
-               AffinityMask))
+               AffinityMask, DetachProcess))
     if (ExecutionFailed)
       *ExecutionFailed = true;
 

llvm/lib/Support/Unix/Program.inc

@@ -173,10 +173,11 @@ toNullTerminatedCStringArray(ArrayRef<StringRef> Strings, StringSaver &Saver) {
 }
 
 static bool Execute(ProcessInfo &PI, StringRef Program,
-                    ArrayRef<StringRef> Args, std::optional<ArrayRef<StringRef>> Env,
+                    ArrayRef<StringRef> Args,
+                    std::optional<ArrayRef<StringRef>> Env,
                     ArrayRef<std::optional<StringRef>> Redirects,
                     unsigned MemoryLimit, std::string *ErrMsg,
-                    BitVector *AffinityMask) {
+                    BitVector *AffinityMask, bool DetachProcess) {
   if (!llvm::sys::fs::exists(Program)) {
     if (ErrMsg)
       *ErrMsg = std::string("Executable \"") + Program.str() +
@@ -202,7 +203,8 @@ static bool Execute(ProcessInfo &PI, StringRef Program,
   // If this OS has posix_spawn and there is no memory limit being implied, use
   // posix_spawn.  It is more efficient than fork/exec.
 #ifdef HAVE_POSIX_SPAWN
-  if (MemoryLimit == 0) {
+  // Cannot use posix_spawn if you would like to detach the process
+  if (MemoryLimit == 0 && !DetachProcess) {
     posix_spawn_file_actions_t FileActionsStore;
     posix_spawn_file_actions_t *FileActions = nullptr;
 
@@ -270,7 +272,7 @@ static bool Execute(ProcessInfo &PI, StringRef Program,
 
     return true;
   }
-#endif
+#endif // HAVE_POSIX_SPAWN
 
   // Create a child process.
   int child = fork();
@@ -307,6 +309,14 @@ static bool Execute(ProcessInfo &PI, StringRef Program,
       }
     }
 
+    if (DetachProcess) {
+      // Detach from controlling terminal
+      if (setsid() == -1) {
+        MakeErrMsg(ErrMsg, "Couldn't detach process, setsid() failed");
+        return false;
+      }
+    }
+
     // Set memory limits
     if (MemoryLimit != 0) {
       SetMemoryLimits(MemoryLimit);

llvm/lib/Support/Windows/Program.inc

@@ -172,10 +172,11 @@ static HANDLE RedirectIO(std::optional<StringRef> Path, int fd,
 } // namespace llvm
 
 static bool Execute(ProcessInfo &PI, StringRef Program,
-                    ArrayRef<StringRef> Args, std::optional<ArrayRef<StringRef>> Env,
+                    ArrayRef<StringRef> Args,
+                    std::optional<ArrayRef<StringRef>> Env,
                     ArrayRef<std::optional<StringRef>> Redirects,
                     unsigned MemoryLimit, std::string *ErrMsg,
-                    BitVector *AffinityMask) {
+                    BitVector *AffinityMask, bool DetachProcess) {
   if (!sys::fs::can_execute(Program)) {
     if (ErrMsg)
       *ErrMsg = "program not executable";
@@ -284,6 +285,8 @@ static bool Execute(ProcessInfo &PI, StringRef Program,
   unsigned CreateFlags = CREATE_UNICODE_ENVIRONMENT;
   if (AffinityMask)
     CreateFlags |= CREATE_SUSPENDED;
+  if (DetachProcess)
+    CreateFlags |= DETACHED_PROCESS;
 
   std::vector<wchar_t> CommandUtf16(Command.size() + 1, 0);
   std::copy(Command.begin(), Command.end(), CommandUtf16.begin());