Merge pull request #2919 from n8sh/issue-20550

Fix Issue 20550 - Use fixed seeds for treaps in GC merged-on-behalf-of: Nicholas Wilson <thewilsonator@users.noreply.github.com>
dlang · Feb 6, 2020 · 0f9cd78 · 0f9cd78
2 parents 51841bc + bc5832a
commit 0f9cd78
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Showing 3 changed files with 6 additions and 63 deletions.
diff --git a/src/gc/impl/conservative/gc.d b/src/gc/impl/conservative/gc.d
@@ -1256,8 +1256,8 @@ struct Gcx
     {
         (cast(byte*)&this)[0 .. Gcx.sizeof] = 0;
         leakDetector.initialize(&this);
-        roots.initialize();
-        ranges.initialize();
+        roots.initialize(0x243F6A8885A308D3UL);
+        ranges.initialize(0x13198A2E03707344UL);
         smallCollectThreshold = largeCollectThreshold = 0.0f;
         usedSmallPages = usedLargePages = 0;
         mappedPages = 0;

diff --git a/src/rt/util/container/treap.d b/src/rt/util/container/treap.d
@@ -27,9 +27,10 @@ nothrow:
         removeAll();
     }
 
-    void initialize()
+    void initialize(ulong randSeed)
     {
-        rand48.defaultSeed();
+        Rand48 _rand48 = { randSeed };
+        rand48 = _rand48;
     }
 
     void insert(E element) @nogc
@@ -262,8 +263,8 @@ unittest
     OP[] ops;
     uint[] opdata;
 
-    treap.initialize();
     srand(cast(uint)time(null));
+    treap.initialize(rand());
 
     uint[] data;
 initialLoop:

diff --git a/src/rt/util/random.d b/src/rt/util/random.d
@@ -11,66 +11,8 @@ struct Rand48
     private ulong rng_state;
 
 @safe @nogc nothrow:
-
-    void defaultSeed() @trusted
-    {
-        version (D_InlineAsm_X86_64)
-        {
-            // RDTSC takes around 22 clock cycles.
-            ulong result = void; // Workaround for LDC issue #950, cannot access struct members in DMD asm.
-            asm @nogc nothrow
-            {
-                rdtsc;
-                // RAX: low 32 bits are low bits of timestamp, high 32 bits are 0.
-                // RDX: low 32 bits are high bits of timestamp, high 32 bits are 0.
-                // We combine these into a 48 bit value instead of a full 64 bits
-                // because `front` and `popFront` only make use of the bottom 48
-                // bits of `rng_state`.
-                shl RDX, 16;
-                xor RDX, RAX;
-                mov result, RDX;
-            }
-            rng_state = result;
-            popFront();
-        }
-        //else version (D_InlineAsm_X86)
-        //{
-        //    // We don't use `rdtsc` with version (D_InlineAsm_X86) because
-        //    // some x86 processors don't support `rdtsc` and because on
-        //    // x86 (but not x86-64) Linux `prctl` can disable a process's
-        //    // ability to use `rdtsc`.
-        //    static assert(0);
-        //}
-        else version (Windows)
-        {
-            // QueryPerformanceCounter takes about 1/4 the time of ctime.time.
-            import core.sys.windows.winbase : QueryPerformanceCounter;
-            QueryPerformanceCounter(cast(long*) &rng_state);
-            popFront();
-        }
-        else version (OSX)
-        {
-            // mach_absolute_time is much faster than ctime.time.
-            import core.time : mach_absolute_time;
-            rng_state = mach_absolute_time();
-            popFront();
-        }
-        else
-        {
-            // Fallback to libc timestamp in seconds.
-            import ctime = core.stdc.time : time;
-            seed((cast(uint) ctime.time(null)));
-        }
-    }
-
 pure:
 
-    void seed(uint seedval)
-    {
-        rng_state = cast(ulong)seedval << 16 | 0x330e;
-        popFront();
-    }
-
     auto opCall()
     {
         auto result = front;