[gjs/gbsneto/external-capture-writer] profiler: Support external SysprofCaptureWriters

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 607f9aa66192d4955f7daf5906b5053c30ce8ff2
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Sat Sep 19 14:57:22 2020 -0300

    profiler: Support external SysprofCaptureWriters
    
    Using environment variables to control the profiler is limiting,
    and when it comes to GNOME Shell, it adds an extra level of
    complexity, since it forces us to start GNOME Shell with the
    right environment set.
    
    Add support for setting a caller-controlled SysprofCaptureWriter.
    The header file treats it as a gpointer to avoid including config.h.
    If an external capture writer is set, it takes precedence over the
    filename and the file descriptor.

 gjs/profiler.cpp | 31 ++++++++++++++++++++++++++++++-
 gjs/profiler.h   |  3 +++
 2 files changed, 33 insertions(+), 1 deletion(-)
---
diff --git a/gjs/profiler.cpp b/gjs/profiler.cpp
index c5113becb..d7c90ef50 100644
--- a/gjs/profiler.cpp
+++ b/gjs/profiler.cpp
@@ -105,6 +105,8 @@ struct _GjsProfiler {
     /* Buffers and writes our sampled stacks */
     SysprofCaptureWriter* capture;
     GSource* periodic_flush;
+
+    SysprofCaptureWriter* target_capture;
 #endif  /* ENABLE_PROFILER */
 
     /* The filename to write to */
@@ -259,6 +261,7 @@ _gjs_profiler_free(GjsProfiler *self)
 #ifdef ENABLE_PROFILER
     g_clear_pointer(&self->capture, sysprof_capture_writer_unref);
     g_clear_pointer(&self->periodic_flush, g_source_destroy);
+    g_clear_pointer(&self->target_capture, sysprof_capture_writer_unref);
 
     if (self->fd != -1)
         close(self->fd);
@@ -429,7 +432,9 @@ gjs_profiler_start(GjsProfiler *self)
     struct itimerspec its = { 0 };
     struct itimerspec old_its;
 
-    if (self->fd != -1) {
+    if (self->target_capture) {
+        self->capture = sysprof_capture_writer_ref(self->target_capture);
+    } else if (self->fd != -1) {
         self->capture = sysprof_capture_writer_new_from_fd(self->fd, 0);
         self->fd = -1;
     } else {
@@ -672,6 +677,30 @@ gjs_profiler_chain_signal(GjsContext *context,
     return false;
 }
 
+/**
+ * gjs_profiler_set_capture_writer:
+ * @self: A #GjsProfiler
+ * @capture: (nullable): A #SysprofCaptureWriter
+ *
+ * Set the capture writer to which profiling data is written when the @self
+ * is stopped.
+ */
+void gjs_profiler_set_capture_writer(GjsProfiler* self, gpointer capture) {
+    g_return_if_fail(self);
+    g_return_if_fail(!self->running);
+
+#ifdef ENABLE_PROFILER
+    g_clear_pointer(&self->target_capture, sysprof_capture_writer_unref);
+    self->target_capture =
+        capture ? sysprof_capture_writer_ref(
+                      reinterpret_cast<SysprofCaptureWriter*>(capture))
+                : NULL;
+#else
+    // Unused in the no-profiler case
+    (void)capture;
+#endif
+}
+
 /**
  * gjs_profiler_set_filename:
  * @self: A #GjsProfiler
diff --git a/gjs/profiler.h b/gjs/profiler.h
index d3518b877..fe8bc5097 100644
--- a/gjs/profiler.h
+++ b/gjs/profiler.h
@@ -42,6 +42,9 @@ typedef struct _GjsProfiler GjsProfiler;
 GJS_EXPORT
 GType gjs_profiler_get_type(void);
 
+GJS_EXPORT
+void gjs_profiler_set_capture_writer(GjsProfiler* self, void* capture);
+
 GJS_EXPORT
 void gjs_profiler_set_filename(GjsProfiler *self,
                                const char  *filename);