Clean up unsync in Base/CommonPlan (#308)

* Remove unsync and unsafe cells from BasePlan and CommonPlan
* Remove unsafe impl Sync for CommonPlan and BasePlan
* Remove the base_spaces feature
* Fix a broken link in rustdoc

Author: qinsoon

Cargo.toml

@@ -48,10 +48,9 @@ default = []
 # -- Non mutally exclusive features --
 
 # spaces
-base_spaces = []
-vm_space = ["base_spaces"]
-ro_space = ["base_spaces"]
-code_space  = ["base_spaces"]
+vm_space = []
+ro_space = []
+code_space  = []
 
 # Run sanity GC
 sanity = []

docs/tutorial/code/mygc_semispace/global.rs

@@ -115,7 +115,7 @@ impl<VM: VMBinding> Plan for MyGC<VM> {
 
     // Modify
     // ANCHOR: prepare
-    fn prepare(&self, tls: VMWorkerThread) {
+    fn prepare(&mut self, tls: VMWorkerThread) {
         self.common.prepare(tls, true);
 
         self.hi
@@ -129,7 +129,7 @@ impl<VM: VMBinding> Plan for MyGC<VM> {
 
     // Modify
     // ANCHOR: release
-    fn release(&self, tls: VMWorkerThread) {
+    fn release(&mut self, tls: VMWorkerThread) {
         self.common.release(tls, true);
         self.fromspace().release();
     }

src/plan/gencopy/global.rs

@@ -128,7 +128,7 @@ impl<VM: VMBinding> Plan for GenCopy<VM> {
         &*ALLOCATOR_MAPPING
     }
 
-    fn prepare(&self, tls: VMWorkerThread) {
+    fn prepare(&mut self, tls: VMWorkerThread) {
         self.common.prepare(tls, true);
         self.nursery.prepare(true);
         if !self.in_nursery() {
@@ -140,7 +140,7 @@ impl<VM: VMBinding> Plan for GenCopy<VM> {
         self.copyspace1.prepare(!hi);
     }
 
-    fn release(&self, tls: VMWorkerThread) {
+    fn release(&mut self, tls: VMWorkerThread) {
         self.common.release(tls, true);
         self.nursery.release();
         if !self.in_nursery() {