lix/src/libexpr/eval.hh
Eelco Dolstra 2d663b502d * Cache the result of file evaluation (i.e, memoize evalFile()). This
prevents files from being evaluated and stored as values multiple
  times.  For instance, evaluation of the ‘system’ attribute in NixOS
  causes ‘nixpkgs/pkgs/lib/lists.nix’ to be evaluated 2019 times.

  Caching gives a modest speedup and a decent memory footprint
  reduction (e.g., from 1.44s to 1.28s, and from 81 MiB to 59 MiB with
  GC_INITIAL_HEAP_SIZE=100000 on my system).
2011-08-06 19:45:43 +00:00

381 lines
9.5 KiB
C++

#ifndef __EVAL_H
#define __EVAL_H
#include "nixexpr.hh"
#include "symbol-table.hh"
#include "hash.hh"
#include <map>
#if HAVE_BOEHMGC
#include <gc/gc_allocator.h>
#endif
namespace nix {
class EvalState;
struct Env;
struct Value;
struct Attr;
/* Attribute sets are represented as a vector of attributes, sorted by
symbol (i.e. pointer to the attribute name in the symbol table). */
#if HAVE_BOEHMGC
typedef std::vector<Attr, gc_allocator<Attr> > BindingsBase;
#else
typedef std::vector<Attr> BindingsBase;
#endif
class Bindings : public BindingsBase
{
public:
iterator find(const Symbol & name);
void sort();
};
typedef enum {
tInt = 1,
tBool,
tString,
tPath,
tNull,
tAttrs,
tList,
tThunk,
tApp,
tLambda,
tBlackhole,
tPrimOp,
tPrimOpApp,
} ValueType;
typedef void (* PrimOpFun) (EvalState & state, Value * * args, Value & v);
struct PrimOp
{
PrimOpFun fun;
unsigned int arity;
Symbol name;
PrimOp(PrimOpFun fun, unsigned int arity, Symbol name)
: fun(fun), arity(arity), name(name) { }
};
struct Value
{
ValueType type;
union
{
int integer;
bool boolean;
/* Strings in the evaluator carry a so-called `context' (the
ATermList) which is a list of strings representing store
paths. This is to allow users to write things like
"--with-freetype2-library=" + freetype + "/lib"
where `freetype' is a derivation (or a source to be copied
to the store). If we just concatenated the strings without
keeping track of the referenced store paths, then if the
string is used as a derivation attribute, the derivation
will not have the correct dependencies in its inputDrvs and
inputSrcs.
The semantics of the context is as follows: when a string
with context C is used as a derivation attribute, then the
derivations in C will be added to the inputDrvs of the
derivation, and the other store paths in C will be added to
the inputSrcs of the derivations.
For canonicity, the store paths should be in sorted order. */
struct {
const char * s;
const char * * context; // must be in sorted order
} string;
const char * path;
Bindings * attrs;
struct {
unsigned int length;
Value * * elems;
} list;
struct {
Env * env;
Expr * expr;
} thunk;
struct {
Value * left, * right;
} app;
struct {
Env * env;
ExprLambda * fun;
} lambda;
PrimOp * primOp;
struct {
Value * left, * right;
} primOpApp;
};
};
struct Env
{
Env * up;
unsigned int prevWith; // nr of levels up to next `with' environment
Value * values[0];
};
struct Attr
{
Symbol name;
Value * value;
Pos * pos;
Attr(Symbol name, Value * value, Pos * pos = &noPos)
: name(name), value(value), pos(pos) { };
Attr() : pos(&noPos) { };
bool operator < (const Attr & a) const
{
return name < a.name;
}
};
/* After overwriting an app node, be sure to clear pointers in the
Value to ensure that the target isn't kept alive unnecessarily. */
static inline void clearValue(Value & v)
{
v.app.right = 0;
}
static inline void mkInt(Value & v, int n)
{
clearValue(v);
v.type = tInt;
v.integer = n;
}
static inline void mkBool(Value & v, bool b)
{
clearValue(v);
v.type = tBool;
v.boolean = b;
}
static inline void mkApp(Value & v, Value & left, Value & right)
{
v.type = tApp;
v.app.left = &left;
v.app.right = &right;
}
void mkString(Value & v, const char * s);
void mkString(Value & v, const string & s, const PathSet & context = PathSet());
void mkPath(Value & v, const char * s);
void copyContext(const Value & v, PathSet & context);
/* Cache for calls to addToStore(); maps source paths to the store
paths. */
typedef std::map<Path, Path> SrcToStore;
struct EvalState;
std::ostream & operator << (std::ostream & str, const Value & v);
class EvalState
{
public:
SymbolTable symbols;
const Symbol sWith, sOutPath, sDrvPath, sType, sMeta, sName,
sSystem, sOverrides;
private:
SrcToStore srcToStore;
bool allowUnsafeEquality;
/* A cache from path names to parse trees. */
std::map<Path, Expr *> parseTrees;
/* A cache from path names to values. */
#if HAVE_BOEHMGC
typedef std::map<Path, Value, std::less<Path>, gc_allocator<std::pair<const Path, Value> > > FileEvalCache;
#else
typedef std::map<Path, Value> FileEvalCache;
#endif
FileEvalCache fileEvalCache;
typedef list<std::pair<string, Path> > SearchPath;
SearchPath searchPath;
SearchPath::iterator searchPathInsertionPoint;
public:
EvalState();
~EvalState();
void addToSearchPath(const string & s);
/* Parse a Nix expression from the specified file. If `path'
refers to a directory, then "/default.nix" is appended. */
Expr * parseExprFromFile(Path path);
/* Parse a Nix expression from the specified string. */
Expr * parseExprFromString(const string & s, const Path & basePath);
/* Evaluate an expression read from the given file to normal
form. */
void evalFile(const Path & path, Value & v);
/* Look up a file in the search path. */
Path findFile(const string & path);
/* Evaluate an expression to normal form, storing the result in
value `v'. */
void eval(Expr * e, Value & v);
void eval(Env & env, Expr * e, Value & v);
/* Evaluation the expression, then verify that it has the expected
type. */
bool evalBool(Env & env, Expr * e);
void evalAttrs(Env & env, Expr * e, Value & v);
/* If `v' is a thunk, enter it and overwrite `v' with the result
of the evaluation of the thunk. If `v' is a delayed function
application, call the function and overwrite `v' with the
result. Otherwise, this is a no-op. */
void forceValue(Value & v);
/* Force a value, then recursively force list elements and
attributes. */
void strictForceValue(Value & v);
/* Force `v', and then verify that it has the expected type. */
int forceInt(Value & v);
bool forceBool(Value & v);
void forceAttrs(Value & v);
void forceList(Value & v);
void forceFunction(Value & v); // either lambda or primop
string forceString(Value & v);
string forceString(Value & v, PathSet & context);
string forceStringNoCtx(Value & v);
/* Return true iff the value `v' denotes a derivation (i.e. a
set with attribute `type = "derivation"'). */
bool isDerivation(Value & v);
/* String coercion. Converts strings, paths and derivations to a
string. If `coerceMore' is set, also converts nulls, integers,
booleans and lists to a string. If `copyToStore' is set,
referenced paths are copied to the Nix store as a side effect.q */
string coerceToString(Value & v, PathSet & context,
bool coerceMore = false, bool copyToStore = true);
/* Path coercion. Converts strings, paths and derivations to a
path. The result is guaranteed to be a canonicalised, absolute
path. Nothing is copied to the store. */
Path coerceToPath(Value & v, PathSet & context);
private:
/* The base environment, containing the builtin functions and
values. */
Env & baseEnv;
unsigned int baseEnvDispl;
public:
/* The same, but used during parsing to resolve variables. */
StaticEnv staticBaseEnv; // !!! should be private
private:
void createBaseEnv();
void addConstant(const string & name, Value & v);
void addPrimOp(const string & name,
unsigned int arity, PrimOpFun primOp);
Value * lookupVar(Env * env, const VarRef & var);
friend class ExprVar;
friend class ExprAttrs;
friend class ExprLet;
Expr * parse(const char * text,
const Path & path, const Path & basePath);
public:
/* Do a deep equality test between two values. That is, list
elements and attributes are compared recursively. */
bool eqValues(Value & v1, Value & v2);
void callFunction(Value & fun, Value & arg, Value & v);
/* Automatically call a function for which each argument has a
default value or has a binding in the `args' map. */
void autoCallFunction(Bindings & args, Value & fun, Value & res);
/* Allocation primitives. */
Value * allocValue();
Env & allocEnv(unsigned int size);
Value * allocAttr(Value & vAttrs, const Symbol & name);
void mkList(Value & v, unsigned int length);
void mkAttrs(Value & v, unsigned int expected);
void mkThunk_(Value & v, Expr * expr);
Value * maybeThunk(Env & env, Expr * expr);
/* Print statistics. */
void printStats();
private:
unsigned long nrEnvs;
unsigned long nrValuesInEnvs;
unsigned long nrValues;
unsigned long nrListElems;
unsigned long nrEvaluated;
unsigned long nrAttrsets;
unsigned long nrOpUpdates;
unsigned long nrOpUpdateValuesCopied;
unsigned int recursionDepth;
unsigned int maxRecursionDepth;
char * deepestStack; /* for measuring stack usage */
friend class RecursionCounter;
friend class ExprOpUpdate;
};
/* Return a string representing the type of the value `v'. */
string showType(const Value & v);
}
#endif /* !__EVAL_H */