coroutine: remove GThread implementation

The GThread implementation is not functional enough to actually
run QEMU reliably. While it was potentially useful for debugging,
we have a scripts/qemugdb/coroutine.py to enable tracing of
ucontext coroutines in GDB, so that removes the only reason for
GThread to exist.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Acked-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

.travis.yml

@@ -86,9 +86,6 @@ matrix:
     - env: CONFIG="--enable-trace-backends=ust"
            TEST_CMD=""
       compiler: gcc
-    - env: CONFIG="--with-coroutine=gthread"
-           TEST_CMD=""
-      compiler: gcc
     - env: CONFIG=""
       os: osx
       compiler: clang
@@ -191,7 +188,7 @@ matrix:
       compiler: none
       env:
         - COMPILER_NAME=gcc CXX=g++-5 CC=gcc-5
-        - CONFIG="--cc=gcc-5 --cxx=g++-5 --disable-pie --disable-linux-user --with-coroutine=gthread"
+        - CONFIG="--cc=gcc-5 --cxx=g++-5 --disable-pie --disable-linux-user"
         - TEST_CMD=""
       before_script:
         - ./configure ${CONFIG} --extra-cflags="-g3 -O0 -fsanitize=thread -fuse-ld=gold" || cat config.log

configure

@@ -1334,7 +1334,7 @@ Advanced options (experts only):
   --oss-lib                path to OSS library
   --cpu=CPU                Build for host CPU [$cpu]
   --with-coroutine=BACKEND coroutine backend. Supported options:
-                           gthread, ucontext, sigaltstack, windows
+                           ucontext, sigaltstack, windows
   --enable-gcov            enable test coverage analysis with gcov
   --gcov=GCOV              use specified gcov [$gcov_tool]
   --disable-blobs          disable installing provided firmware blobs
@@ -4418,10 +4418,8 @@ fi
 # check and set a backend for coroutine
 
 # We prefer ucontext, but it's not always possible. The fallback
-# is sigcontext. gthread is not selectable except explicitly, because
-# it is not functional enough to run QEMU proper. (It is occasionally
-# useful for debugging purposes.)  On Windows the only valid backend
-# is the Windows-specific one.
+# is sigcontext. On Windows the only valid backend is the Windows
+# specific one.
 
 ucontext_works=no
 if test "$darwin" != "yes"; then
@@ -4460,7 +4458,7 @@ else
       feature_not_found "ucontext"
     fi
     ;;
-  gthread|sigaltstack)
+  sigaltstack)
     if test "$mingw32" = "yes"; then
       error_exit "only the 'windows' coroutine backend is valid for Windows"
     fi
@@ -4472,14 +4470,7 @@ else
 fi
 
 if test "$coroutine_pool" = ""; then
-  if test "$coroutine" = "gthread"; then
-    coroutine_pool=no
-  else
-    coroutine_pool=yes
-  fi
-fi
-if test "$coroutine" = "gthread" -a "$coroutine_pool" = "yes"; then
-  error_exit "'gthread' coroutine backend does not support pool (use --disable-coroutine-pool)"
+  coroutine_pool=yes
 fi
 
 if test "$debug_stack_usage" = "yes"; then