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Sampling Raster Values at Specific Coordinates with Python

If you are a two-degree marketplace like Uber, you cater to millions of users requesting a ride through your driver partners accepting and fulfilling those requests. For a three-degree marketplace like Swiggy, there is another static component added (like restaurants or stores), where delivery partners pick up the orders. Borrowing from the quote, “Everything happens somewhere” — all of these events and actions described take place at a specific location! Often, companies end up not leveraging the in their data and running their analyses at the city level. But, cities are too large, geographically diverse and the parameters vary way too much! lat/long component Area level polygons are much more practical but still broad. They don’t have uniform shapes or sizes and are subject to changes very frequently. Even the zones or clusters drawn by the operations teams’ local knowledge require updating and have arbitrary edges. Making sense of your spatial data and deriving precise insights requires these analyses to become more granular and uniform. brings that fine granularity to the table. It works brilliantly in bucketing all your lat-longs into “cells”. These cells can also be clustered to represent a particular neighborhood or area and can be aggregated at different levels. Grid system Hence, this system becomes critical to crunch large spatial data sets to match the supply & demand fragmented across the city. What is meant by grids? In Spatial Data Science, we use grids that are regular polygons repeating over a surface, edge to edge to cover any space without overlaps and gaps — a phenomenon called Each cell can be assigned a unique id for spatial indexing (aggregating the points inside that cell). tessellation . A wide variety of grids of different shapes have been proposed including squares, rectangles, triangles, hexagons or diamonds. The covers the entire surface of the earth. global grid system If you are a hyperlocal, on-demand company, grids as small as can be very useful to run models that work in context to location and in include surge pricing in high demand areas, promotions in low demand areas & distribution models of delivery folks on the ground. 0.5 sq. km real-time. Examples What are the different grid types? There are just three types of grids or that can tessellate: squares, equilateral triangles & hexagons. 1. Square grids: The most common application of square grids occurs in raster datasets and geohashes. For the scope of this piece, we will focus on geohashes. is a hierarchical data structure to transform a 2D spatial point (lat & long) into a short string of alphabets and numbers. They divide the world into a grid of 32 cells with 4 rows and 8 columns. Geohash You can keep splitting up each cell into a grid of 32 cells. Thus, the longer the string of the geohash, the higher the accuracy! You can also easily identify if geohashes are close together if they can have a common prefix. So, the longer the common prefix, the closer they are. For example, the coordinate pair near the tip of the peninsula of Jutland, Denmark produces a slightly shorter hash of (57.64911, 10.40744) u4pruydqqvj. [1] 2. Triangular grids: Triangular grids are not very commonly used. Besides, their unfamiliarity, one of the reasons for that is they have a large perimeter and a small area which means it’s harder to piece them together on the map. Another reason is that each triangle is connected to only three adjacent triangles, which limits the number of options to move and to make connections. (Check the image below) Moreover, while for hexagons and squares, there are always two faces parallel to each other, for triangles, there are two directions in which lines are parallel centered from the axis of movement. Thus, in a way, there are not completely symmetrical. [2] 3. Hexagonal grids: Besides looking appealing, hexagons are more symmetric than geohashes. They are very close to circles in terms of shape to provide a more accurate sampling. [3] As a result, this system has been increasingly adopted by companies like Uber. A hex grid and triangular grids are a dual of each other — putting a dot in the center of each hexagon & connecting them to all the adjacent ones, you get a triangular grid and vice versa! Fun fact: [4] Moving on the vertices of a hexagonal grid is equivalent to playing in the spaces on a triangular grid. Square grids, on the other hand, are a dual of themselves. Why hexagons? At , one question that we get a lot from our customers is, “why are we using hexbins and not geohashes?” Locale Well, the choice depends on your exact use case and you would have to make some tradeoffs, no matter what you use. So, let’s take some parameters and deep dive. This diagram shows the distance of the center of triangles, square & hexagon to its neighbors. Distance from Nearest Cells: A triangle has three kinds of distance (through the edge, vertex and across the center of the edge), a square has two (across the edge & the diagonal) and hexagon only has one — another reason why triangles are not really favored. This property of hexagons makes it very easy to perform analysis and is preferred when your analysis includes aspects of connectivity or movement. [4] All the neighbors in a hexagon form a ring around it with equal radius. The function provides grid cells within distance “k” of an origin index. In the diagram below, here is the of the shaded hexagon and square. kRing 1st kRing Fitting on Curved Surfaces: Hexagons are the densest way to pack circles in tessellation and reduce . (Circles have the least perimeter to area ratio but can’t form a continuous grid). edge effects The more similar a polygon is to a circle, the closer the points near the border area are to the center. Thus, any point inside a hexagon is closer to its center as compared to an equal-area square or triangle. Now, when large areas come into play and the curvature of the earth is important to consider, hexagons are therefore better suited to fit the curvature and suffer less distortion. [5] Explicit Patterns in Data: Hexagons allow any in the data to show easily and explicitly because they break up lines. curvature of the patterns For linear figures like squares and rectangles, this becomes tricky. These shapes draw our attention to the straight, unbroken and parallel lines which hinder the patterns present in the data. Refer to the diagram below. [6] Why geohashes? That brings me to my next question, “When would someone use fishnets or square grids?” Aggregation/ Division of Cells: Different kinds of models require different granularity and that’s where aggregation and division become important. If you need to increase the spatial resolution of a square grid, you just need to divide it into 4. Similarly, to aggregate, you need to combine four grids into one. For hexagons, aggregations and divisions are not uniform at different scales as shown in the image below. The finer cells are only approximately contained in the parent cell. [7] Squares are preferred over hexagons for hierarchical analysis. Combining square grids is fairly simple. No spatial operations are necessary for combing multiple grids built on the same template — you can use matrix algebra. Very Intuitive & Familiar: We also think in terms of “ ”. Up, down, left, right are simple to understand. We have built cities and civilizations on squares and rectangles. Since our primary coordinate system is squared, people find it difficult to work on other systems. squares They are also sometimes used for connectivity analysis as they have eight neighbors (including diagonals). Some Real-Life Examples Hexagons are found widely in nature. For example, honeycombs, graphite, benzene, silicene etc. Chinese Checkers is played on a hex grid and several variants of chess have also been invented for a hex board. The hex grid is a distinguishing feature of the games from many wargame publishers, and a few other games (such as The Settlers of Catan)! [8] About Locale: At Locale, we are building an “ operational ” analytics platform using location data for supply and operations teams in on-demand companies. If you want to delve further, check our website out or get in touch with me on LinkedIn or Twitter . Originally posted here . Read Similar: Geospatial Clustering: Types and Use Cases [ ] Link A Guide to Kickstart with Geospatial Analysis [ ] Link References: If you wish to read more, check out the links to delve further: [1] https://en.wikipedia.org/wiki/Geohash [2] https://boardgames.stackexchange.com/questions/633/why-are-there-fewer-board-games-with-a-triangular-grid [3] https://www.redblobgames.com/grids/hexagons/ [4] http://www-cs-students.stanford.edu/~amitp/game-programming/grids/ [5] https://pro.arcgis.com/en/pro-app/tool-reference/spatial-statistics/h-whyhexagons.htm [4] https://www.sciencedirect.com/science/article/pii/S0304380007001949 [5] http://strimas.com/spatial/hexagonal-grids/ [6] https://gis.stackexchange.com/questions/82362/what-are-the-benefits-of-hexagonal-sampling-polygons [7] https://en.wikipedia.org/wiki/Hex_map [8] https://en.wikipedia.org/wiki/Hexagonal_tiling%5C Previously published at https://blog.locale.ai/spatial-modelling-tidbits-honeycomb-or-fishnets/

Why Do We Use Hexagons And Not Sqaures to Aggregate Location Data

MORE ENQUIRIES INTO MASON-BEES

DUCKS—GOOSE—PEACOCK—TURKEY—GUINEA-FOWL—CANARY-BIRD—GOLD-FISH—HIVE-BEES—SILK-MOTHS

is a new source control system developed by Meta. Recently, it gains the ability to work with GitHub. I’m curious about how it works, so I decided to give it a try and end up using it daily on my company’s repositories. If you want to try it out, check . Sapling their documentation here Stacked PRs When developing, I usually create a single commit for each PR and stack them together. To give an example, let’s say we are developing the sign-up feature: user inputs their email address, password, and we send them a nice welcome email. From the backend perspective, we need to create a new user, verify that the user doesn’t exist, and send the email. We need to touch the implementation of the cache package, add an email package, then finally implement the sign-up logic. This can be represented as a stack of PRs: Update package to add a new method. the cache Add . It uses the package to prevent sending duplicated emails. the email sending system cache Implement . It depends on the two changes above. the sign-up logic : This help reviewers with separation of concern. Smaller, isolated changes are easier to be reviewed. They can check the PRs one by one, with each PR containing independent logic. Of course, the email system still requires the cache package to be updated, but we can still review the email system in isolation. The benefit When the origin gets updated, we’ll pull the changes and rebase the PRs on top of the origin, push the changes, get reviewed, and merge. *The downside:*It requires discipline to keep the PRs small and isolated. Usually, while developing the upper PRs, we need to make some changes in the lower PRs. This can be annoying since we have to keep track of what changes in what PR, or constantly switch between PRs to make changes, then rebase the upper ones. git checkout mybranch/signup   # checkout sign up branch
vim features/signup/signup.go  # make changes to signup
vim lib/email/email.go         # make changes to email package

git add features/signup        # commit the signup changes        
git commit --amend             
git stash                      # stash the cache changes
git checkout mybranch/email    # checkout email branch
git stash pop                  # apply the cache changes
git add lib/email              # commit the email changes
git commit --amend
git checkout mybranch/signup   # checkout sign up branch again
git rebase mybranch/email      # rebase the signup branch on top of email branch Too much switching, and too many commands to type. It’s not fun. Enter sapling Sapling is a new git client. It encourages the use of stacked PR. It will automatically rebase the PRs on top of each other, so we don’t have to do it manually. Given the following commit structure, presented by calling the command: sl sl
  @  00f1749f6  30 minutes ago  oliver
  │  implement user signup
  │
  @  e0dbbc80e  50 minutes ago  oliver
  │  implement email package
  │
  o  4f6928029  Yesterday at   oliver
╭─╯  update cache package
│
o  876f46044  Today at 07:45  remote/main The workflow with sapling will be: sl goto 00f1749f6              # checkout the sign up code
vim features/signup/signup.go  # make changes to signup
vim lib/email/email.go         # make changes to email package

sl absorb                      # magic 👻 With only a single command , sapling will: sl absorb Amend the changes to the email commit. email.go Amend the changes to the signup commit. signup.go Rebase the signup commit on top of the email commit. Your changes will be absorbed into the PRs, and the PRs will be rebased on top of each other. You don’t have to do it manually as before. With only a single command. Well done! 👻 My experience with sapling I’m using sapling for a few weeks now. It’s a new tool, so there are some problems, but the overall experience is great. Commonly used commands View repository status: : show the commit-graph (or smart-log) sl : show the status of the current branch sl status Moving between commits: : checkout the commit. sl goto <commit> , : checkout the next/previous commit. sl next sl prev Working with commits: , , : add/remove/untrack files. sl add sl remove sl forget : commit the changes as a new commit. sl commit : edit the commit message. sl metaedit : absorb the changes into the PRs, and rebase the PRs on top of each other. sl absorb : rebase the PRs on top of each other. sl rebase While adds all changes to the staging area, including new files, deleted files; the corresponding command will only add new files to the staging area. To remove files, we must use . This will be a bit annoying when committing vendor files, since we have to list all deleted files to remove them. I’m not sure if there is a better way: git add sl add sl remove $ sl status

? vendor/github.com/sample/cache/v2/caching.go
? vendor/github.com/sample/cache/v2/stripe.go
! vendor/github.com/sample/cache/v1/deprecated.go
! vendor/github.com/sample/cache/v1/formatter.go $ sl add vendor

A vendor/github.com/sample/cache/v2/caching.go
A vendor/github.com/sample/cache/v2/stripe.go
! vendor/github.com/sample/cache/v1/deprecated.go
! vendor/github.com/sample/cache/v1/formatter.go # Have to list all deleted files to remove, is there a better way? 😞
$ sl remove vendor/github.com/sample/cache/v1/deprecated.go \
            vendor/github.com/sample/cache/v1/formatter.go

A vendor/github.com/sample/cache/v2/caching.go
A vendor/github.com/sample/cache/v2/stripe.go
R vendor/github.com/sample/cache/v1/deprecated.go
R vendor/github.com/sample/cache/v1/formatter.go Pushing PRs to GitHub Sapling provides 2 ways of pushing PRs to GitHub: and . Each has different trade-offs. I prefer using the command: sl pr sl ghstack sl pr It creates a PR for each commit. It pushes the PRs to GitHub in the order of the commits. It’s easier to understand as commits stacks nicely on each other. It works well and can be reviewed with GitHub’s UI. Another benefit, it does not require write permission to the repository, in case you do a fork. The command creates a more complex web of PRs. And there are a lot of times when it fails to push the PRs. Try again won’t work. No available fixes. Have to duplicate these PRs again and risk spamming my company repositories. I don’t recommend it. sl ghstack Reviewing PRs Sapling recommends using for reviewing. But I find it slow, less responsive, and sometimes gives wrong file changes. I prefer using GitHub’s UI. When pushing PRs with , it creates a single commit for each PR. So the reviewer can open the latest commit, and review the changes. Just one more extra click compared to the usual review flow: reviewstack sl pr Go to Commits tab. Choose the latest commit. Review and add comments. These comments will appear on the PR as usual. Other things It requires cloning a new repository, so you can’t use your familiar git commands. It won’t work with your existing tools, IDE, etc. You have to use the UI to view changes. sl web Give it a try! Sapling is great. While there are a few troubles, and it requires a small learning curve, it pays back in the end. Stacking, pushing, and reviewing PRs is much easier. Give it a try! __ Also published . here

Experimenting With Sapling, the New Git Client From Meta

Welcome to other chapters of Let’s Understand Chrome V8 Dispatch is responsible for scheduling bytecode, which is equivalent to registering EIP++, and jumps to the next bytecode. Dispatch consists of two parts, one is a dispatch table and the other is the physical register. The table is an array that contains all bytecode addresses. V8 uses the physical register to dispatch bytecode for getting greater efficiency. 1. Dispatch Table The dispatch table is an array of pointers, which is used to store the address of the bytecode processing program. The array type is Code, and the Code Class is below: class Code: public HeapObject {
    public: NEVER_READ_ONLY_SPACE
    using Flags = uint32_t;
    #define CODE_KIND_LIST(V)\
    V(OPTIMIZED_FUNCTION)\
    V(BYTECODE_HANDLER)\
    V(STUB)\
    V(BUILTIN)\
    V(REGEXP)\
    V(WASM_FUNCTION)\
    V(WASM_TO_CAPI_FUNCTION)\
    V(WASM_TO_JS_FUNCTION)\
    V(JS_TO_WASM_FUNCTION)\
    V(JS_TO_JS_FUNCTION)\
    V(WASM_INTERPRETER_ENTRY)\
    V(C_WASM_ENTRY)
    enum Kind {
      #define DEFINE_CODE_KIND_ENUM(name) name,
        CODE_KIND_LIST(DEFINE_CODE_KIND_ENUM)
      #undef DEFINE_CODE_KIND_ENUM
      NUMBER_OF_KINDS
    };
    static
    const char * Kind2String(Kind kind);
    #ifdef ENABLE_DISASSEMBLER
    const char * GetName(Isolate * isolate) const;
    V8_EXPORT_PRIVATE void Disassemble(const char * name, std::ostream & os,
      Address current_pc = kNullAddress);
    #endif
    //................omit................
  }; : In the isolate, there is another pointer array that is the same type as the dispatch table. It holds all the Builtins addresses, which can confuse beginners easily. Note The dispatch table is maintained by BuildWithMacroAssembler, code is below: Code BuildWithMacroAssembler(Isolate * isolate, int32_t builtin_index,
    MacroAssemblerGenerator generator,
    const char * s_name) {
    HandleScope scope(isolate);
    // Canonicalize handles, so that we can share constant pool entries pointing
    // to code targets without dereferencing their handles.
    CanonicalHandleScope canonical(isolate);
    constexpr int kBufferSize = 32 * KB;
    byte buffer[kBufferSize];
    MacroAssembler masm(isolate, BuiltinAssemblerOptions(isolate, builtin_index),
      CodeObjectRequired::kYes,
      ExternalAssemblerBuffer(buffer, kBufferSize));
    masm.set_builtin_index(builtin_index);
    DCHECK(!masm.has_frame());
    generator( & masm);
    int handler_table_offset = 0;
    // JSEntry builtins are a special case and need to generate a handler table.
    DCHECK_EQ(Builtins::KindOf(Builtins::kJSEntry), Builtins::ASM);
    DCHECK_EQ(Builtins::KindOf(Builtins::kJSConstructEntry), Builtins::ASM);
    DCHECK_EQ(Builtins::KindOf(Builtins::kJSRunMicrotasksEntry), Builtins::ASM);
    if (Builtins::IsJSEntryVariant(builtin_index)) {
      handler_table_offset = HandlerTable::EmitReturnTableStart( & masm);
      HandlerTable::EmitReturnEntry( &
        masm, 0, isolate -> builtins() -> js_entry_handler_offset());
    }
    //.....................................................
    //................omit.............................
  } You can see regarding how to debug the BuildWithMacroAssembler. When the value of the parameter builtin_index is 65, the function pointer generator points to which is responsible for maintaining the Dispatch table, code is below: Chapter 9 Generate_InterpreterEnterBytecodeDispatch static void Generate_InterpreterEnterBytecode(MacroAssembler * masm) {
    // Set the return address to the correct point in the interpreter entry
    // trampoline.
    Label builtin_trampoline, trampoline_loaded;
    Smi interpreter_entry_return_pc_offset(
      masm -> isolate() -> heap() -> interpreter_entry_return_pc_offset());
    DCHECK_NE(interpreter_entry_return_pc_offset, Smi::kZero);
    // If the SFI function_data is an InterpreterData, the function will have a
    // custom copy of the interpreter entry trampoline for profiling. If so,
    // get the custom trampoline, otherwise grab the entry address of the global
    // trampoline.
    __ movq(rbx, Operand(rbp, StandardFrameConstants::kFunctionOffset));
    __ LoadTaggedPointerField(
      rbx, FieldOperand(rbx, JSFunction::kSharedFunctionInfoOffset));
    __ LoadTaggedPointerField(
      rbx, FieldOperand(rbx, SharedFunctionInfo::kFunctionDataOffset));
    __ CmpObjectType(rbx, INTERPRETER_DATA_TYPE, kScratchRegister);
    __ j(not_equal, & builtin_trampoline, Label::kNear);
    __ movq(rbx,
      FieldOperand(rbx, InterpreterData::kInterpreterTrampolineOffset));
    __ addq(rbx, Immediate(Code::kHeaderSize - kHeapObjectTag));
    __ jmp( & trampoline_loaded, Label::kNear);
    __ bind( & builtin_trampoline);
    // TODO(jgruber): Replace this by a lookup in the builtin entry table.
    __ movq(rbx,
      __ ExternalReferenceAsOperand(
        ExternalReference::
        address_of_interpreter_entry_trampoline_instruction_start(
          masm -> isolate()),
        kScratchRegister));
    __ bind( & trampoline_loaded);
    __ addq(rbx, Immediate(interpreter_entry_return_pc_offset.value()));
    __ Push(rbx);
    // Initialize dispatch table register.
    __ Move(
      kInterpreterDispatchTableRegister,
      ExternalReference::interpreter_dispatch_table_address(masm -> isolate()));
    // Get the bytecode array pointer from the frame.
    __ movq(kInterpreterBytecodeArrayRegister,
      Operand(rbp, InterpreterFrameConstants::kBytecodeArrayFromFp));
    if (FLAG_debug_code) {
      // Check function data field is actually a BytecodeArray object.
      __ AssertNotSmi(kInterpreterBytecodeArrayRegister);
      __ CmpObjectType(kInterpreterBytecodeArrayRegister, BYTECODE_ARRAY_TYPE,
        rbx);
      __ Assert(
        equal,
        AbortReason::kFunctionDataShouldBeBytecodeArrayOnInterpreterEntry);
    }
    // Get the target bytecode offset from the frame.
    __ movq(kInterpreterBytecodeOffsetRegister,
      Operand(rbp, InterpreterFrameConstants::kBytecodeOffsetFromFp));
    __ SmiUntag(kInterpreterBytecodeOffsetRegister,
      kInterpreterBytecodeOffsetRegister);
    // Dispatch to the target bytecode.
    __ movzxbq(r11, Operand(kInterpreterBytecodeArrayRegister,
      kInterpreterBytecodeOffsetRegister, times_1, 0));
    __ movq(kJavaScriptCallCodeStartRegister,
      Operand(kInterpreterDispatchTableRegister, r11,
        times_system_pointer_size, 0));
    __ jmp(kJavaScriptCallCodeStartRegister);
  }
  //================================separation=========================
  void Builtins::Generate_InterpreterEnterBytecodeDispatch(MacroAssembler * masm) {
    Generate_InterpreterEnterBytecode(masm);
  } In the above code, the is the entry point of bytecode dispatch, and the is the key code that implements the bytecode dispatch. Here are two important concepts: Generate_InterpreterEnterBytecodeDispatch Generate_InterpreterEnterBytecode The is a Builtin and its index is 65. (The index may be dissimilar in different V8 versions) Generate_InterpreterEnterBytecodeDispatch V8 uses a physical register to manage the dispatch table, the name of the register is . Using the physical register can avoid the push and pop of the dispatch table frequently, to improve efficiency. kInterpreterDispatchTableRegister Here are the key lines of code： Line 35, loads the dispatch table to the A register. Line 37 of code, take out the table address from the isolate. The implementation of A is in the below three functions. (1) ExternalReference ExternalReference::interpreter_dispatch_table_address(
  Isolate * isolate) {
  return ExternalReference(isolate -> interpreter() -> dispatch_table_address());
}
interpreter::Interpreter * interpreter() const {
  return interpreter_;
}
Address dispatch_table_address() {
  return reinterpret_cast < Address > ( & dispatch_table_[0]);
} Line 39 takes out the bytecode array from the stack. (2) Line 51 takes out the offset of the target bytecode from the bytecode array. (3) Lines 56 and 58 calculate the target bytecode address and store the address in kJavaScriptCallCodeStartRegister. (4) Line 61 jumps to register kJavaScriptCallCodeStartRegister and executes bytecode. Figure 1 is the call stack. (5) 2. TailCall The Dispatch() is the last step in a bytecode, so its alias is the tail call. Let’s look at a few bytecodes： IGNITION_HANDLER(StaGlobal, InterpreterAssembler) {
    TNode < Context > context = GetContext();
    //omit..............
    Goto( & end);
    Bind( & no_feedback);
    CallRuntime(Runtime::kStoreGlobalICNoFeedback_Miss, context, value, name);
    Goto( & end);
    Bind( & end);
    Dispatch(); // !!! this is the tail call.
  }
  IGNITION_HANDLER(LdaContextSlot, InterpreterAssembler) {
    TNode < Context > context = CAST(LoadRegisterAtOperandIndex(0));
    TNode < IntPtrT > slot_index = Signed(BytecodeOperandIdx(1));
    TNode < Uint32T > depth = BytecodeOperandUImm(2);
    TNode < Context > slot_context = GetContextAtDepth(context, depth);
    TNode < Object > result = LoadContextElement(slot_context, slot_index);
    SetAccumulator(result);
    Dispatch(); //!!! here also is.
  }
  IGNITION_HANDLER(LdaImmutableContextSlot, InterpreterAssembler) {
    TNode < Context > context = CAST(LoadRegisterAtOperandIndex(0));
    TNode < IntPtrT > slot_index = Signed(BytecodeOperandIdx(1));
    TNode < Uint32T > depth = BytecodeOperandUImm(2);
    TNode < Context > slot_context = GetContextAtDepth(context, depth);
    TNode < Object > result = LoadContextElement(slot_context, slot_index);
    SetAccumulator(result);
    Dispatch(); //!!! here 
  } The above three bytecodes all end with Dispatch(). Below is the code of Dispatch: void InterpreterAssembler::Dispatch() {
    Comment("========= Dispatch");
    DCHECK_IMPLIES(Bytecodes::MakesCallAlongCriticalPath(bytecode_), made_call_);
    TNode < IntPtrT > target_offset = Advance();
    TNode < WordT > target_bytecode = LoadBytecode(target_offset);
    if (Bytecodes::IsStarLookahead(bytecode_, operand_scale_)) {
      target_bytecode = StarDispatchLookahead(target_bytecode);
    }
    DispatchToBytecode(target_bytecode, BytecodeOffset());
  } The 2nd line is the comment function. When debugging, we can use its output information to locate the execution position. The 4th line takes out the offset of the target(next) bytecode. The 5th line loads the target bytecode. The 9th line calls which calls eventually. DspatchToBytecode() DispatchToBytecodeHandlerEntry() void InterpreterAssembler::DispatchToBytecodeHandlerEntry(
  TNode < RawPtrT > handler_entry, TNode < IntPtrT > bytecode_offset) {
  // Propagate speculation poisoning.
  TNode < RawPtrT > poisoned_handler_entry =
    UncheckedCast < RawPtrT > (WordPoisonOnSpeculation(handler_entry));
  TailCallBytecodeDispatch(InterpreterDispatchDescriptor {},
    poisoned_handler_entry, GetAccumulatorUnchecked(),
    bytecode_offset, BytecodeArrayTaggedPointer(),
    DispatchTablePointer());
} In , parameter 1 is the target bytecode and 2 is the offset of the bytecode. Parameter 1 is used to load the bytecode handler and 2 is used to load operands. Then call , which is below: DispatchToBytecodeHandlerEntry TailCallBytecodeDispatch template < class...TArgs >
    void CodeAssembler::TailCallBytecodeDispatch(
      const CallInterfaceDescriptor & descriptor, TNode < RawPtrT > target,
        TArgs...args) {
      DCHECK_EQ(descriptor.GetParameterCount(), sizeof...(args));
      auto call_descriptor = Linkage::GetBytecodeDispatchCallDescriptor(
        zone(), descriptor, descriptor.GetStackParameterCount());
      Node * nodes[] = {
        target,
        args...
      };
      CHECK_EQ(descriptor.GetParameterCount() + 1, arraysize(nodes));
      raw_assembler() -> TailCallN(call_descriptor, arraysize(nodes), nodes);
    } In the above code, the 5th line creates the descriptor, as below: CallDescriptor * Linkage::GetBytecodeDispatchCallDescriptor(
    Zone * zone,
    const CallInterfaceDescriptor & descriptor,
      int stack_parameter_count) {
    const int register_parameter_count = descriptor.GetRegisterParameterCount();
    const int parameter_count = register_parameter_count + stack_parameter_count;
    DCHECK_EQ(descriptor.GetReturnCount(), 1);
    LocationSignature::Builder locations(zone, 1, parameter_count);
    locations.AddReturn(regloc(kReturnRegister0, descriptor.GetReturnType(0)));
    for (int i = 0; i < parameter_count; i++) {
      if (i < register_parameter_count) {
        // The first parameters go in registers.
        Register reg = descriptor.GetRegisterParameter(i);
        MachineType type = descriptor.GetParameterType(i);
        locations.AddParam(regloc(reg, type));
      } else {
        int stack_slot = i - register_parameter_count - stack_parameter_count;
        locations.AddParam(LinkageLocation::ForCallerFrameSlot(
          stack_slot, MachineType::AnyTagged()));
      }
    }
    MachineType target_type = MachineType::Pointer();
    LinkageLocation target_loc = LinkageLocation::ForAnyRegister(target_type);
    const CallDescriptor::Flags kFlags =
      CallDescriptor::kCanUseRoots | CallDescriptor::kFixedTargetRegister;
    return new(zone) CallDescriptor( // --
      CallDescriptor::kCallAddress, // kind
      target_type, // target MachineType
      target_loc, // target location
      locations.Build(), // location_sig
      stack_parameter_count, // stack_parameter_count
      Operator::kNoProperties, // properties
      kNoCalleeSaved, // callee-saved registers
      kNoCalleeSaved, // callee-saved fp
      kFlags, // flags
      descriptor.DebugName());
  } In , parameter 2 is the target bytecode, and parameter 3 is the stack parameter count. This function is used to apply for register resources and create a . The gives what parameters to supply when executing a bytecode. The comments on lines 24 to 25 give its layout. GetBytecodeDispatchCallDescriptor CallDescriptor CallDescriptor In , the on the 9th line is below, we see that it’s parameter 1 is . TailCallBytecodeDispatch TailCallN() CallDescriptor void RawMachineAssembler::TailCallN(CallDescriptor * call_descriptor,
    int input_count, Node *
    const * inputs) {
    // +1 is for target.
    DCHECK_EQ(input_count, call_descriptor -> ParameterCount() + 1);
    Node * tail_call =
      MakeNode(common() -> TailCall(call_descriptor), input_count, inputs);
    schedule() -> AddTailCall(CurrentBlock(), tail_call);
    current_block_ = nullptr;
  } The 5th line generates a node. In the 7th line adds the node to the end of the current basic block. So far, the dispatch is completed and the next bytecode is started to execute. Figure 2 shows the function call stack. AddTailCall() Okay, that wraps it up for this share. I’ll see you guys next time, take care! Please reach out to me if you have any issues. : qq9123013 : v8blink@outlook.com WeChat Email Also published . here

Let's Understand Chrome V8 — Chapter 11: Bytecode Dispatch 

What is a BESS (Battery Energy Storage System) and How Does it Work?

Hi there! We are the Navigine team. For 8 years we have been providing integrated positioning mobile technologies that enable advanced indoor navigation and proximity solutions. Today we decided to open the doors to our technology and talk about how to scan BLE devices when the Android application is killed and in background mode. Background BLE scans for Android devices could be divided into two different groups depending on the mechanisms used for scheduling background tasks. During the last few years, Android changed background processing and added Doze mode, limited implicit broadcasts, and limited background behavior and. But most of the new solutions will not work for old Android versions and all the old solutions will be killed by Android in new versions. So in this article, we will review two different strategies for scanning in the background — for versions before API 26 (Oreo) and after. Background tasks in Android devices with an API level less than 26 (Oreo) For all old android versions up to Android Oreo, there is a working method for scanning in the background using alarm manager and service with the broadcast receiver. The broadcast receiver will get wake up alarm and start service where will be initialized and started for 10 seconds. After this time SDK will be finished and service will be killed. This alarm could be set up with at least a one-minute intervals and will work without any restrictions in old devices. Navigine SDK public { public onReceive(Context context, Intent intent) { action = intent.getAction(); { (action.equals( )) {        
        PendingIntent pendingIntent = PendingIntent.getBroadcast(
            context, , Intent( ),
            PendingIntent.FLAG_UPDATE_CURRENT);

        AlarmManager alarmService = (AlarmManager)context.getSystemService(Context.ALARM_SERVICE); (alarmService != )
          alarmService.setRepeating(AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + , * , pendingIntent);
      } (action.equals( )) {
        context.startService( Intent(context, NavigineService.class));
      }
    } (Throwable e) {
      Logger.d(TAG, , Log.getStackTraceString(e));
    }
  }
} class NavigineReceiverExample extends BroadcastReceiver // here you need to receive some action from intent and depending on this action start service or set repeating alarm void String try if "START" 0 new "WAKE" if null 5000 60 1000 else if "WAKE" new catch 1 NavigineReceiverExample.java for devices with an API level less than 26 Inside the service class, you can declare handling intent from the broadcast receiver and starting or other manipulations you want to do. This solution will not work in Android devices with the version starting from 26 because Android will not allow starting the service when your app is killed so here we need better solutions. Navigine SDK Background tasks starting from Android Oreo Starting from API 26 Android started blocking services running when the device is killed and provided few solutions for running your tasks in the background. But the main difficulty is, these solutions also will not work in Doze mode (If a user leaves a device unplugged and stationary for a period of time, with the screen off, the device enters Doze mode). Here is the restrictions list when app entered Doze mode: Screenshot from Google developers website Further, we will talk about each solution that we found and will provide code examples. Each of them could be used if you will decide not to fight with Doze mode. As we need to scan BLE devices every few minutes we need to run periodic background tasks. Also, we will provide two more solutions that will ignore Doze mode but will need more resources or will have extra notifications. Periodic J ob Scheduler . Job Scheduler could be used starting from Android API level 23 and replaced Service + Alarm Manager for running background tasks. Periodic Job Scheduler could be waked up at least every 15 minutes and has a lot of opportunities if you need some conditions for your job scheduler like requiring to run only if the device has an internet connection, should be charging, etc. For using this method you should extend the JobService class and override method for starting your task. And start Job Scheduler to run a periodic job. Do not forget to add your service to your manifest file. Here is the code example of how to start periodic job scheduler: onStartJob JobScheduler jobShedulerService = (JobScheduler) context.getSystemService(Context.JOB_SCHEDULER_SERVICE);
jobShedulerService.schedule( JobInfo.Builder(ID, ComponentName(context, NavigineJobService.class.getName()))
  .setRequiredNetworkType(JobInfo.NETWORK_TYPE_ANY) .setPeriodic( * * ) .setRequiresCharging( ) .build()); new new // any network type 15 60 1000 // every 15 minutes false // if device should be charging Periodic job scheduler This solution runs perfectly while the device is not in the Doze mode, otherwise, it will just skip jobs and start new periods. In the screenshot below you can see how well it works. In this particular case, we added flex-time to the periodic job and it starts earlier than it should. Logcat screenshot for periodic job scheduler. Common Alarm Managers with or will work well only when the device is not in Doze mode because Android will ignore them and reschedule for next time. Using . will allow the alarm to be called, but the job scheduler will be ignored even in this case. However, you can add method to your job scheduler and it will run this scheduled job when the device exits Doze mode. Here is the code example for the method of our BroadcastReceiver extension: Alarm with . setAndAllowWhileIdle() and JobScheduler. .set() .setRepeating() setAndAllowWhileIdle() . setOverrideDeadline(time in milliseconds) onReceive { {
    String  action = intent.getAction(); { (action.equals( )) {   
        Intent wakeIntent = Intent( );
          wakeIntent.setClass(context, YourReceiver.class);
        
        PendingIntent pendingIntent = PendingIntent.getBroadcast(
            context, ,
            wakeIntent,
            PendingIntent.FLAG_UPDATE_CURRENT);

        AlarmManager alarmService = (AlarmManager)context.getSystemService(Context.ALARM_SERVICE); (alarmService != )
          alarmService.setAndAllowWhileIdle(AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + * * , pendingIntent);
      } (action.equals( )) {
        
        JobScheduler jobShedulerService = (JobScheduler) context.getSystemService(Context.JOB_SCHEDULER_SERVICE);
        jobShedulerService.schedule( JobInfo.Builder( , ComponentName(context, YourJobClass.class))
                .setRequiredNetworkType(JobInfo.NETWORK_TYPE_ANY)
                .setMinimumLatency( )
                .setOverrideDeadline( * * )
                .build()); 

        Intent wakeIntent = Intent( );
        wakeIntent.setClass(context, YourReceiver.class);

        PendingIntent pendingIntent = PendingIntent.getBroadcast(
            context, ,
            wakeIntent,
            PendingIntent.FLAG_UPDATE_CURRENT);

        AlarmManager alarmService = (AlarmManager)context.getSystemService(Context.ALARM_SERVICE); (alarmService != )
          alarmService.setAndAllowWhileIdle(AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + Default.NAVIGINE_JOB_SERVICE_WAKEUP_TIME * , pendingIntent);
      }
    } (Throwable e) {
      Logger.d(TAG, , Log.getStackTraceString(e));
    }
  }
} public class NavigineBroadcastReceiverExample extends BroadcastReceiver // here you need to receive some action from intent and depending on this action start service or set repeating alarm public void onReceive (Context context, Intent intent) try if "START" new "WAKE" 0 if null 15 60 1000 else if "WAKE" new 1 new 0L 15 60 1000 new "WAKE" 0 if null 1000 catch 1 Broadcast Receiver example using Alarm Manager and Job Scheduler In our case, we decided to kill these jobs if more than 30 minutes passed after they have been scheduled. This solution also will not solve the problem with running background tasks in Doze mode, but jobs will not be skipped like in a periodic job scheduler. Keep in mind, that even in Doze mode these alarms will be ignored if you try to call them more then once every 9 minutes. Waking up every 5 minutes with an Alarm Manager and starting Job Scheduler. (Not in Doze mode) Unfortunately, none of these methods will allow you to execute background tasks in Doze mode, even WorkManager will not help you with this task. But there are few other solutions you can use. Foreground services will run without any cancels and without entering Doze mode, so your background tasks will run infinitely. But this solution has one disadvantage, your app will always have pinned notification in the devices’ status bar. Running foreground service. Screenshot of foreground service running after the app has been killed. As you can see in this screenshot, the user will always see this notification which could not be canceled. Using foreground service will increase the chances that your application will be removed faster than it could be. Also, it’s worth noting that your application will use more power and device resources. Here is the foreground service code example: { {
        String input = intent.getStringExtra( );
        createNotificationChannel();
        
        PendingIntent pendingIntent = PendingIntent.getActivity( , , Intent( , YourActivity.class), );
        
        Notification notification = NotificationCompat.Builder( , CHANNEL_ID)
                .setContentTitle( )
                .setContentText(input)
                .setSmallIcon(R.drawable.ic_stat_name)
                .setContentIntent(pendingIntent)
                .build();
        
        startForeground( , notification); START_NOT_STICKY;
    } {
        NotificationChannel serviceChannel = NotificationChannel(
                CHANNEL_ID, ,
                NotificationManager.IMPORTANCE_DEFAULT);
      
        getSystemService(NotificationManager.class).createNotificationChannel(serviceChannel);
    }
} public class ForegroundService extends Service @Override public int onStartCommand (Intent intent, flags, startId) int int "inputExtra" this 0 new this 0 new this "Foreground Service" 1 // here is the code you wanna run in background return private void createNotificationChannel () new "Foreground Service Channel" Foreground Service example Another way to run background tasks even in Doze mode to send notifications to your application from the server. These notifications will force your application to exit Doze mode and yourи job could be done. But in this case, you will need to spend more resources on running and maintaining your service. You can find more info about using Firebase Cloud Messaging to run your background services by . Using push notifications. this link Conclusion Over time Google hardens the ability to run background tasks, so developers need to come up with new solutions and tricks, like sending push notifications for waking the device up from Doze mode. In defense of the android, we can say that they are using their actions to protect users from unwanted and unnecessary actions in the background that will use the phone’s resources and perform unwanted, and sometimes malicious tasks. By the way, the above solutions will help you to work respecting the requirements of Android or bypass the Doze mode.

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