Subzero: Add locking to prepare for multithreaded translation.

src/IceGlobalContext.h

 //===- subzero/src/IceGlobalContext.h - Global context defs -----*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file declares aspects of the compilation that persist across
 // multiple functions.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef SUBZERO_SRC_ICEGLOBALCONTEXT_H
 #define SUBZERO_SRC_ICEGLOBALCONTEXT_H
 
 #include <memory>
+#include <mutex>
 
 #include "IceDefs.h"
 #include "IceClFlags.h"
 #include "IceIntrinsics.h"
 #include "IceRNG.h"
 #include "IceTimerTree.h"
 #include "IceTypes.h"
 
 namespace Ice {
 
 class ClFlags;
 class FuncSigType;
 
-// This class collects rudimentary statistics during translation.
-class CodeStats {
-  CodeStats(const CodeStats &) = delete;
-  CodeStats &operator=(const CodeStats &) = default;
-
-public:
-  CodeStats()
-      : InstructionsEmitted(0), RegistersSaved(0), FrameBytes(0), Spills(0),
-        Fills(0) {}
-  void reset() { *this = CodeStats(); }
-  void updateEmitted(uint32_t InstCount) { InstructionsEmitted += InstCount; }
-  void updateRegistersSaved(uint32_t Num) { RegistersSaved += Num; }
-  void updateFrameBytes(uint32_t Bytes) { FrameBytes += Bytes; }
-  void updateSpills() { ++Spills; }
-  void updateFills() { ++Fills; }
-  void dump(const IceString &Name, Ostream &Str);
-
-private:
-  uint32_t InstructionsEmitted;
-  uint32_t RegistersSaved;
-  uint32_t FrameBytes;
-  uint32_t Spills;
-  uint32_t Fills;
-};
-
-// TODO: Accesses to all non-const fields of GlobalContext need to
-// be synchronized, especially the constant pool, the allocator, and
-// the output streams.
 class GlobalContext {
   GlobalContext(const GlobalContext &) = delete;
   GlobalContext &operator=(const GlobalContext &) = delete;
 
+  // CodeStats collects rudimentary statistics during translation.
+  class CodeStats {
+    CodeStats(const CodeStats &) = delete;
+    CodeStats &operator=(const CodeStats &) = default;
+
+  public:
+    CodeStats()
+      : InstructionsEmitted(0), RegistersSaved(0), FrameBytes(0), Spills(0),
+        Fills(0) {}
+    void reset() { *this = CodeStats(); }
+    void updateEmitted(uint32_t InstCount) { InstructionsEmitted += InstCount; }
+    void updateRegistersSaved(uint32_t Num) { RegistersSaved += Num; }
+    void updateFrameBytes(uint32_t Bytes) { FrameBytes += Bytes; }
+    void updateSpills() { ++Spills; }
+    void updateFills() { ++Fills; }
+    void dump(const IceString &Name, Ostream &Str);
+
+  private:
+    uint32_t InstructionsEmitted;
+    uint32_t RegistersSaved;
+    uint32_t FrameBytes;
+    uint32_t Spills;
+    uint32_t Fills;
+  };
+
+  // ThreadContext contains thread-local data.  This data can be
+  // combined/reduced as needed after all threads complete.
+  class ThreadContext {
+    ThreadContext(const ThreadContext &) = delete;
+    ThreadContext &operator=(const ThreadContext &) = delete;
+  public:
+    ThreadContext() {}
+    CodeStats StatsFunction;
+    std::vector<TimerStack> Timers;
+  };
+
+  typedef std::recursive_mutex GlobalLockType;

[JF, 2015/01/15 16:28:39]

Could you instead have separate allocator lock and stats lock?

[Jim Stichnoth, 2015/01/17 18:44:17]

Done.  I went ahead and made several finer-grain locks: allocator, stats,
timers, and constant pool.  (There's still room to refine the constant pool lock
to be per-type, and/or to keep a thread-local cache.)

+
 public:
   GlobalContext(Ostream *OsDump, Ostream *OsEmit, ELFStreamer *ELFStreamer,
                 VerboseMask Mask, TargetArch Arch, OptLevel Opt,
                 IceString TestPrefix, const ClFlags &Flags);
   ~GlobalContext();
 
   // Returns true if any of the specified options in the verbose mask
   // are set.  If the argument is omitted, it checks if any verbose
   // options at all are set.
   VerboseMask getVerbose() const { return VMask; }
   bool isVerbose(VerboseMask Mask = IceV_All) const { return VMask & Mask; }
   void setVerbose(VerboseMask Mask) { VMask = Mask; }
   void addVerbose(VerboseMask Mask) { VMask |= Mask; }
   void subVerbose(VerboseMask Mask) { VMask &= ~Mask; }
 
-  Ostream &getStrDump() { return *StrDump; }
-  Ostream &getStrEmit() { return *StrEmit; }
+  // The dump and emit streams need to be used by only one thread at a
+  // time.  This is done by exclusively reserving the streams via
+  // lockStr() and unlockStr().  The OstreamLocker class can be used
+  // to conveniently manage this.
+  //
+  // The model is that a thread grabs the stream lock, then does an
+  // arbitrary amount of work during which far-away callees may grab
+  // the stream and do something with it, and finally the thread
+  // releases the stream lock.  This allows large chunks of output to
+  // be dumped or emitted without risking interleaving from multiple
+  // threads.  When a worker locks the streams via lockStr(), we use
+  // IsStrLocked to verify that it wasn't already locked (i.e. no
+  // recursive lockStr() calls).  When a worker grabs one of the
+  // streams via getStrDump() or getStrEmit(), we lock StrLock
+  // (recursively, if lockStr() was correctly used, hence the need for
+  // recursive_mutex) and check that IsStrLocked is set.
+  void lockStr() {
+    StrLock.lock();
+    assert(!isStrLocked());
+    IsStrLocked = true;
+  }
+  void unlockStr() {
+    assert(isStrLocked());
+    IsStrLocked = false;
+    StrLock.unlock();
+  }
+  // Test whether we are already holding StrLock, by first doing a
+  // lock() and when it (eventually) succeeds, checking that we didn't
+  // recursively lock it.
+  bool isStrLocked() {
+    StrLock.lock();
+    bool WasLocked = IsStrLocked;
+    StrLock.unlock();
+    return WasLocked;
+  }
+  Ostream &getStrDump() {
+    assert(isStrLocked());
+    return *StrDump;
+  }
+  Ostream &getStrEmit() {
+    assert(isStrLocked());
+    return *StrEmit;
+  }
 
   TargetArch getTargetArch() const { return Arch; }
   OptLevel getOptLevel() const { return Opt; }
 
   // When emitting assembly, we allow a string to be prepended to
   // names of translated functions.  This makes it easier to create an
   // execution test against a reference translator like llc, with both
   // translators using the same bitcode as input.
   IceString getTestPrefix() const { return TestPrefix; }
   IceString mangleName(const IceString &Name) const;
@@ skipping 11 matching lines @@
   Constant *getConstantDouble(double Value);
   // Returns a symbolic constant.
   Constant *getConstantSym(RelocOffsetT Offset, const IceString &Name,
                            bool SuppressMangling);
   // Returns an undef.
   Constant *getConstantUndef(Type Ty);
   // Returns a zero value.
   Constant *getConstantZero(Type Ty);
   // getConstantPool() returns a copy of the constant pool for
   // constants of a given type.
-  ConstantList getConstantPool(Type Ty) const;
+  ConstantList getConstantPool(Type Ty);
   // Returns a new function declaration, allocated in an internal
   // memory pool.  Ownership of the function is maintained by this
   // class instance.
   FunctionDeclaration *newFunctionDeclaration(const FuncSigType *Signature,
                                               unsigned CallingConv,
                                               unsigned Linkage, bool IsProto);
 
   // Returns a new global variable declaration, allocated in an
   // internal memory pool.  Ownership of the function is maintained by
   // this class instance.
   VariableDeclaration *newVariableDeclaration();
 
   const ClFlags &getFlags() const { return Flags; }
 
   bool isIRGenerationDisabled() const {
     return ALLOW_DISABLE_IR_GEN ? getFlags().DisableIRGeneration : false;
   }
 
   // Allocate data of type T using the global allocator.
-  template <typename T> T *allocate() { return Allocator.Allocate<T>(); }
+  template <typename T> T *allocate() {
+    std::lock_guard<GlobalLockType> L(GlobalLock);
+    return Allocator.Allocate<T>();
+  }
 
   const Intrinsics &getIntrinsicsInfo() const { return IntrinsicsInfo; }
 
   // TODO(wala,stichnot): Make the RNG play nicely with multithreaded
   // translation.
   RandomNumberGenerator &getRNG() { return RNG; }
 
   ELFObjectWriter *getObjectWriter() const { return ObjectWriter.get(); }
 
   // Reset stats at the beginning of a function.
   void resetStats() {
     if (ALLOW_DUMP)
-      StatsFunction.reset();
+      TLS->StatsFunction.reset();
   }
   void dumpStats(const IceString &Name, bool Final = false);
   void statsUpdateEmitted(uint32_t InstCount) {
-    if (!ALLOW_DUMP)
+    if (!ALLOW_DUMP || !getFlags().DumpStats)
       return;
-    StatsFunction.updateEmitted(InstCount);
+    TLS->StatsFunction.updateEmitted(InstCount);
+    std::lock_guard<GlobalLockType> L(GlobalLock);
     StatsCumulative.updateEmitted(InstCount);
   }
   void statsUpdateRegistersSaved(uint32_t Num) {
-    if (!ALLOW_DUMP)
+    if (!ALLOW_DUMP || !getFlags().DumpStats)
       return;
-    StatsFunction.updateRegistersSaved(Num);
+    TLS->StatsFunction.updateRegistersSaved(Num);
+    std::lock_guard<GlobalLockType> L(GlobalLock);
     StatsCumulative.updateRegistersSaved(Num);
   }
   void statsUpdateFrameBytes(uint32_t Bytes) {
-    if (!ALLOW_DUMP)
+    if (!ALLOW_DUMP || !getFlags().DumpStats)
       return;
-    StatsFunction.updateFrameBytes(Bytes);
+    TLS->StatsFunction.updateFrameBytes(Bytes);
+    std::lock_guard<GlobalLockType> L(GlobalLock);
     StatsCumulative.updateFrameBytes(Bytes);
   }
   void statsUpdateSpills() {
-    if (!ALLOW_DUMP)
+    if (!ALLOW_DUMP || !getFlags().DumpStats)
       return;
-    StatsFunction.updateSpills();
+    TLS->StatsFunction.updateSpills();
+    std::lock_guard<GlobalLockType> L(GlobalLock);
     StatsCumulative.updateSpills();
   }
   void statsUpdateFills() {
-    if (!ALLOW_DUMP)
+    if (!ALLOW_DUMP || !getFlags().DumpStats)
       return;
-    StatsFunction.updateFills();
+    TLS->StatsFunction.updateFills();
+    std::lock_guard<GlobalLockType> L(GlobalLock);
     StatsCumulative.updateFills();
   }
 
   // These are predefined TimerStackIdT values.
   enum TimerStackKind {
     TSK_Default = 0,
     TSK_Funcs,
     TSK_Num
   };
 
+  TimerStackIdT newTimerStackID(const IceString &Name);
   TimerIdT getTimerID(TimerStackIdT StackID, const IceString &Name);
-  TimerStackIdT newTimerStackID(const IceString &Name);
   void pushTimer(TimerIdT ID, TimerStackIdT StackID = TSK_Default);
   void popTimer(TimerIdT ID, TimerStackIdT StackID = TSK_Default);
   void resetTimer(TimerStackIdT StackID);
   void setTimerName(TimerStackIdT StackID, const IceString &NewName);
   void dumpTimers(TimerStackIdT StackID = TSK_Default,
                   bool DumpCumulative = true);
 
 private:
+  // GlobalLock is the default coarse-grain lock for accessing members
+  // of GlobalContext.  As contention becomes an issue, more
+  // fine-grain locks can be added.
+  GlobalLockType GlobalLock;
+
+  // StrLock is a global lock on the dump and emit output streams.
+  // IsStrLocked is used to validate the locking protocol, and can
+  // only be meaningfully inspected when StrLock is held.  Note that
+  // in a production build, the dump and emit streams are not used in
+  // any meaningful way, so this locking is more for
+  // development/debugging purposes.
+  typedef std::recursive_mutex StrLockType;
+  StrLockType StrLock;
+  bool IsStrLocked;
+
   Ostream *StrDump; // Stream for dumping / diagnostics
   Ostream *StrEmit; // Stream for code emission
 
   ArenaAllocator<> Allocator;
   VerboseMask VMask;
   std::unique_ptr<class ConstantPool> ConstPool;
   Intrinsics IntrinsicsInfo;
   const TargetArch Arch;
   const OptLevel Opt;
   const IceString TestPrefix;
   const ClFlags &Flags;
   RandomNumberGenerator RNG;
   std::unique_ptr<ELFObjectWriter> ObjectWriter;
-  CodeStats StatsFunction;
   CodeStats StatsCumulative;
   std::vector<TimerStack> Timers;
   std::vector<GlobalDeclaration *> GlobalDeclarations;
 
+  std::vector<ThreadContext *> AllThreadContexts;
+  // Each thread has its own TLS pointer which is also held in
+  // AllThreadContexts.
+  thread_local static ThreadContext *TLS;
+
   // Private helpers for mangleName()
   typedef llvm::SmallVector<char, 32> ManglerVector;
   void incrementSubstitutions(ManglerVector &OldName) const;
 };
 
 // Helper class to push and pop a timer marker.  The constructor
 // pushes a marker, and the destructor pops it.  This is for
 // convenient timing of regions of code.
 class TimerMarker {
   TimerMarker(const TimerMarker &) = delete;
@@ skipping 14 matching lines @@
     if (ALLOW_DUMP && Active)
       Ctx->popTimer(ID);
   }
 
 private:
   TimerIdT ID;
   GlobalContext *const Ctx;
   bool Active;
 };
 
+// Helper class for locking the streams and then automatically
+// unlocking them.
+class OstreamLocker {
+private:
+  OstreamLocker() = delete;
+  OstreamLocker(const OstreamLocker &) = delete;
+  OstreamLocker &operator=(const OstreamLocker &) = delete;
+
+public:
+  explicit OstreamLocker(GlobalContext *Ctx) : Ctx(Ctx) { Ctx->lockStr(); }
+  ~OstreamLocker() { Ctx->unlockStr(); }
+
+private:
+  GlobalContext *const Ctx;
+};
+
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEGLOBALCONTEXT_H