[RFC 2/4] app: optionaly return thread ID of newly started app

[Justin Cinkelj]

The thread ID of thread running new app main() function is returned.

Signed-off-by: Justin Cinkelj <justin.cink...@xlab.si>
---
 core/app.cc        | 12 ++++++++++--
 include/osv/app.hh |  7 ++++++-
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/core/app.cc b/core/app.cc
index ad3145f..6ea5d6e 100644
--- a/core/app.cc
+++ b/core/app.cc
@@ -133,8 +133,12 @@ shared_app_t application::run(const std::string& command,
     return app;
 }
 
-void run(const std::vector<std::string>& args) {
-    application::run(args);
+void run(const std::vector<std::string>& args, pid_t *pid) {
+    auto app = application::run(args);
+    if (pid) {
+        *pid = app->get_main_thread_id();
+        assert((*pid) != 0);
+    }
 }
 
 shared_app_t application::run_and_join(const std::string& command,
@@ -419,6 +423,10 @@ std::string application::get_command()
     return _command;
 }
 
+pid_t application::get_main_thread_id() {
+    return pthread_gettid_np(_thread);
+}
+
 // For simplicity, we will not reuse bits in the bitmap, since no destructor is
 // assigned to the program. In that case, a simple counter would do. But coding
 // this way is easy, and make this future extension simple.
diff --git a/include/osv/app.hh b/include/osv/app.hh
index 6fa503a..90bc7ce 100644
--- a/include/osv/app.hh
+++ b/include/osv/app.hh
@@ -176,6 +176,11 @@ public:
      */
     std::string get_command();
 
+    /**
+      * Returns thread_id/PID of thread running app main() function.
+      */
+    pid_t get_main_thread_id();
+
     std::shared_ptr<application_runtime> runtime() const { return _runtime; }
     std::shared_ptr<elf::object> lib() const { return _lib; }
 
@@ -238,7 +243,7 @@ namespace osv {
  * Creates a new app
  * args Arguments passed to the program's main() function.
  */
-void run(const std::vector<std::string>& args);
+void run(const std::vector<std::string>& args, pid_t *pid=nullptr);
 
 namespace this_application {
 
-- 
2.9.3

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