Hi there,
I am encountering a cgo problem (unsure, most likely) when
migrating an old C library to Go.
A cgo call calls a component of the C library, which
internally creates an OS thread and then calls libpango
(pango_cairo_font_map_get_default() call).
The original pure C code is able to go through the pango call:
printf("before call");
font_map = pango_cairo_font_map_get_default();
printf("after call");
Outputs:
before call
after call
After involving Go, the code stuck at the Pango call after its
first calling, and prints the following warning and critical
message from GLib:
before call
(process:1): GLib-GObject-WARNING **: cannot register existing type
'PangoFontMap'
(process:1): GLib-CRITICAL **: g_once_init_leave: assertion 'result != 0'
failed
(process:1): GLib-GObject-CRITICAL **: g_type_register_static: assertion
'parent_type > 0' failed
(process:1): GLib-CRITICAL **: g_once_init_leave: assertion 'result != 0'
failed
(process:1): GLib-GObject-CRITICAL **: g_type_register_static: assertion
'parent_type > 0' failed
(process:1): GLib-GObject-WARNING **: cannot register existing type
'PangoCairoFontMap'
Call chain:
round1: go code --> goroutine --> cgo --> c --> dlopen --> back to go -->
hold a pointer points to C memory in Go--> goroutine --> cgo --> pass the
pointer to C -->
pthread_create --> pango_font_map_get_default() --> success!
round2: same call chain --> fail! message in above
My understanding of pango_font_map_get_default() is
the call will always a success because of thread safe
(after v1.36, internal font-map managed by pango is per-thread),
and can be called multiple times, i.e. the call must success.
Thus, a suspicion leads to somehow cgo or Go memory allocator
influence the C side.
My questions are:
1. Is my suspicion reasonable and correct?
2. Why an error when involving cgo?
3. Are memories in a non-Go thread completely isolated to Go
memory per-non-Go thread?
4. Are C memories allocated in a cgo call always stands in
the same sharing heap even threading?
5. Any other theories and how cloud possibly solve the problem?
6. If I am asking a wrong question, could you shoot any ideas of
solving the issue described above?
Thank you very much in advance.
Best,
changkun
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