Move /src to /subprojects

This will facilitate breaking up Nix into multiple packages for each
component with Meson.

subprojects/libexpr/eval-gc.cc

@@ -0,0 +1,117 @@
+#include "error.hh"
+#include "environment-variables.hh"
+#include "eval-settings.hh"
+#include "config-global.hh"
+#include "serialise.hh"
+#include "eval-gc.hh"
+
+#if HAVE_BOEHMGC
+
+#  include <pthread.h>
+#  if __FreeBSD__
+#    include <pthread_np.h>
+#  endif
+
+#  include <gc/gc.h>
+#  include <gc/gc_cpp.h>
+#  include <gc/gc_allocator.h>
+
+#  include <boost/coroutine2/coroutine.hpp>
+#  include <boost/coroutine2/protected_fixedsize_stack.hpp>
+#  include <boost/context/stack_context.hpp>
+
+#endif
+
+namespace nix {
+
+#if HAVE_BOEHMGC
+/* Called when the Boehm GC runs out of memory. */
+static void * oomHandler(size_t requested)
+{
+    /* Convert this to a proper C++ exception. */
+    throw std::bad_alloc();
+}
+
+static inline void initGCReal()
+{
+    /* Initialise the Boehm garbage collector. */
+
+    /* Don't look for interior pointers. This reduces the odds of
+       misdetection a bit. */
+    GC_set_all_interior_pointers(0);
+
+    /* We don't have any roots in data segments, so don't scan from
+       there. */
+    GC_set_no_dls(1);
+
+    /* Enable perf measurements. This is just a setting; not much of a
+       start of something. */
+    GC_start_performance_measurement();
+
+    GC_INIT();
+
+    GC_set_oom_fn(oomHandler);
+
+    /* Set the initial heap size to something fairly big (25% of
+       physical RAM, up to a maximum of 384 MiB) so that in most cases
+       we don't need to garbage collect at all.  (Collection has a
+       fairly significant overhead.)  The heap size can be overridden
+       through libgc's GC_INITIAL_HEAP_SIZE environment variable.  We
+       should probably also provide a nix.conf setting for this.  Note
+       that GC_expand_hp() causes a lot of virtual, but not physical
+       (resident) memory to be allocated.  This might be a problem on
+       systems that don't overcommit. */
+    if (!getEnv("GC_INITIAL_HEAP_SIZE")) {
+        size_t size = 32 * 1024 * 1024;
+#  if HAVE_SYSCONF && defined(_SC_PAGESIZE) && defined(_SC_PHYS_PAGES)
+        size_t maxSize = 384 * 1024 * 1024;
+        long pageSize = sysconf(_SC_PAGESIZE);
+        long pages = sysconf(_SC_PHYS_PAGES);
+        if (pageSize != -1)
+            size = (pageSize * pages) / 4; // 25% of RAM
+        if (size > maxSize)
+            size = maxSize;
+#  endif
+        debug("setting initial heap size to %1% bytes", size);
+        GC_expand_hp(size);
+    }
+}
+
+static size_t gcCyclesAfterInit = 0;
+
+size_t getGCCycles()
+{
+    assertGCInitialized();
+    return static_cast<size_t>(GC_get_gc_no()) - gcCyclesAfterInit;
+}
+
+#endif
+
+static bool gcInitialised = false;
+
+void initGC()
+{
+    if (gcInitialised)
+        return;
+
+#if HAVE_BOEHMGC
+    initGCReal();
+
+    gcCyclesAfterInit = GC_get_gc_no();
+#endif
+
+    // NIX_PATH must override the regular setting
+    // See the comment in applyConfig
+    if (auto nixPathEnv = getEnv("NIX_PATH")) {
+        globalConfig.set("nix-path", concatStringsSep(" ", EvalSettings::parseNixPath(nixPathEnv.value())));
+    }
+
+    gcInitialised = true;
+}
+
+void assertGCInitialized()
+{
+    assert(gcInitialised);
+}
+
+} // namespace nix