Allow Java VM iterate over allocated objects

[asmundak]

Summary

Objects may move during the garbage collection, and JVM needs to notify ThreadAnalyzer about that. The new function __tsan_java_find eliminates the need to maintain these objects both in ThreadAnalyzer and JVM.

[dvyukov]

Just small nits and we are ready to land.

lib/tsan/rtl/tsan_interface_java.cc

157

Please drop "(jptr)" and { } around body.
The conversion is not necessary as jptr is some integer, and at the end of the function you do "return 0;" anyway.
Tsan codebase generally does not use { } around 1-statement if/for bodies.

... or you can drop this whole check, the condition should be handled fine by the loop (the loop will terminate instantly as "from < to" is false).

167

Wanted to ask if JVM can ever allocate 0-size blocks. But I see that we have the following checks in __tsan_java_alloc:

CHECK_NE(size, 0);
CHECK_EQ(size % kHeapAlignment, 0);

So we should be good.

lib/tsan/rtl/tsan_interface_java.h

61

s/Returns 0 there are no/Returns 0 if there are no/

test/tsan/java_find.cc

23

s/in \n/in\n/
space at the end of line

[asmundak]

Addressed reviewer comments

[dvyukov]

LGTM
committed in 289682

lib/tsan/rtl/tsan_interface_java.h

 // It ensures necessary synchronization between
 // java object creation and finalization.
 void __tsan_java_finalize() INTERFACE_ATTRIBUTE;
+// Finds the first allocated memory block in the [*from_ptr, to) range, saves
+// its address in *from_ptr and returns its size. Returns 0 if there are no
+// allocated memory blocks in the range.
+jptr __tsan_java_find(jptr *from_ptr, jptr to) INTERFACE_ATTRIBUTE;
 
 // Mutex lock.
 // Addr is any unique address associated with the mutex.

lib/tsan/rtl/tsan_interface_java.cc

   }
 }
 
+jptr __tsan_java_find(jptr *from_ptr, jptr to) {
+  SCOPED_JAVA_FUNC(__tsan_java_find);
+  DPrintf("#%d: java_find(&%p, %p)\n", *from_ptr, to);
+  CHECK_EQ((*from_ptr) % kHeapAlignment, 0);
+  CHECK_EQ(to % kHeapAlignment, 0);
+  CHECK_GE(*from_ptr, jctx->heap_begin);
+  CHECK_LE(to, jctx->heap_begin + jctx->heap_size);
+  for (uptr from = *from_ptr; from < to; from += kHeapAlignment) {
+    MBlock *b = ctx->metamap.GetBlock(from);
+    if (b) {
+      *from_ptr = from;
+      return b->siz;
+    }
+  }
+  return 0;
+}
+
 void __tsan_java_finalize() {
   SCOPED_JAVA_FUNC(__tsan_java_finalize);
   DPrintf("#%d: java_mutex_finalize()\n", thr->tid);

test/tsan/java.h

 int  __tsan_java_fini();
 void __tsan_java_alloc(jptr ptr, jptr size);
 void __tsan_java_free(jptr ptr, jptr size);
+jptr __tsan_java_find(jptr *from_ptr, jptr to);
 void __tsan_java_move(jptr src, jptr dst, jptr size);
 void __tsan_java_finalize();
 void __tsan_java_mutex_lock(jptr addr);

test/tsan/java_find.cc

+// RUN: %clangxx_tsan -O1 %s -o %t && %run %t 2>&1 | FileCheck %s
+#include "java.h"
+
+int const kHeapSize = 1024 * 1024;
+
+static void verify_find(jptr from, jptr to, jptr expected_addr,
+                        jptr expected_size) {
+  jptr addr = from;
+  jptr size = __tsan_java_find(&addr, to);
+  if (expected_size) {
+    if (!size) {
+      fprintf(stderr, "FAILED: range: [%p..%p): found nothing\n", (void *)from,
+              (void *)to);
+      return;
+    } else if (expected_size != size) {
+      fprintf(stderr, "FAILED: range: [%p..%p): wrong size, %lu instead of %lu\n",
+              (void *)from, (void *)to, size, expected_size);
+      return;
+    }
+  } else if (size) {
+    fprintf(stderr,
+            "FAILED: range [%p..%p): did not expect to find anything here\n",
+            (void *)from, (void *)to);
+    return;
+  } else {
+    return;
+  }
+  if (expected_addr != addr) {
+    fprintf(
+        stderr,
+        "FAILED: range [%p..%p): expected to find object at %p, found at %p\n",
+        (void *)from, (void *)to, (void *)expected_addr, (void *)addr);
+  }
+}
+
+int main() {
+  const jptr jheap = (jptr)malloc(kHeapSize + 8) + 8;
+  const jptr jheap_end = jheap + kHeapSize;
+  __tsan_java_init(jheap, kHeapSize);
+  const jptr addr1 = jheap;
+  const int size1 = 16;
+  __tsan_java_alloc(jheap, size1);
+
+  const jptr addr2 = addr1 + size1;
+  const int size2 = 32;
+  __tsan_java_alloc(jheap + size1, size2);
+
+  const jptr addr3 = addr2 + size2;
+  const int size3 = 1024;
+  __tsan_java_alloc(jheap + size1 + size2, size3);
+
+  const jptr addr4 = addr3 + size3;
+
+  verify_find(jheap, jheap_end, addr1, size1);
+  verify_find(jheap + 8, jheap_end, addr2, size2);
+  verify_find(addr2 + 8, jheap_end, addr3, size3);
+  verify_find(addr3 + 8, jheap_end, 0, 0);
+
+  __tsan_java_move(addr2, addr4, size2);
+  verify_find(jheap + 8, jheap_end, addr3, size3);
+  verify_find(addr3 + 8, jheap_end, addr4, size2);
+  verify_find(addr4 + 8, jheap_end, 0, 0);
+
+  fprintf(stderr, "DONE\n");
+  return 0;
+}
+
+// CHECK-NOT: FAILED
+// CHECK: DONE