RAII Scope

RAII ties a resource's lifetime to an object's scope.
RAII RAII means resource acquisition is initialization: acquire in the constructor and release in the destructor.
                            example
                            label = "load", workUnits = 3 (default)label = "save"label = "sync"workUnits = 1workUnits = 5
                        

                            raii_scope.cpp
                        
Replay: real traced execution (multi-file project)

                            #include <iostream>
#include <string>

class ScopeLog {
private:
    std::string name;

public:
    ScopeLog(std::string label) {
        name = label;
        std::cout << "enter=" << name << std::endl;
    }

    ~ScopeLog() {
        std::cout << "leave=" << name << std::endl;
    }
};

int runJob(std::string label, int workUnits) {
    ScopeLog scope(label);
    int total = 0;
    for (int i = 1; i <= workUnits; i++) {
        total += i;
    }
    return total;
}

int main() {
    std::string label = "load";
    int workUnits = 3;

    int total = runJob(label, workUnits);

    std::cout << "total=" << total << std::endl;
    return 0;
}
#include <iostream>
#include <string>

class ScopeLog {
private:
    std::string name;

public:
    ScopeLog(std::string label) {
        name = label;
        std::cout << "enter=" << name << std::endl;
    }

    ~ScopeLog() {
        std::cout << "leave=" << name << std::endl;
    }
};

int runJob(std::string label, int workUnits) {
    ScopeLog scope(label);
    int total = 0;
    for (int i = 1; i <= workUnits; i++) {
        total += i;
    }
    return total;
}

int main() {
    std::string label = "save";
    int workUnits = 3;

    int total = runJob(label, workUnits);

    std::cout << "total=" << total << std::endl;
    return 0;
}
#include <iostream>
#include <string>

class ScopeLog {
private:
    std::string name;

public:
    ScopeLog(std::string label) {
        name = label;
        std::cout << "enter=" << name << std::endl;
    }

    ~ScopeLog() {
        std::cout << "leave=" << name << std::endl;
    }
};

int runJob(std::string label, int workUnits) {
    ScopeLog scope(label);
    int total = 0;
    for (int i = 1; i <= workUnits; i++) {
        total += i;
    }
    return total;
}

int main() {
    std::string label = "sync";
    int workUnits = 3;

    int total = runJob(label, workUnits);

    std::cout << "total=" << total << std::endl;
    return 0;
}
#include <iostream>
#include <string>

class ScopeLog {
private:
    std::string name;

public:
    ScopeLog(std::string label) {
        name = label;
        std::cout << "enter=" << name << std::endl;
    }

    ~ScopeLog() {
        std::cout << "leave=" << name << std::endl;
    }
};

int runJob(std::string label, int workUnits) {
    ScopeLog scope(label);
    int total = 0;
    for (int i = 1; i <= workUnits; i++) {
        total += i;
    }
    return total;
}

int main() {
    std::string label = "load";
    int workUnits = 1;

    int total = runJob(label, workUnits);

    std::cout << "total=" << total << std::endl;
    return 0;
}
#include <iostream>
#include <string>

class ScopeLog {
private:
    std::string name;

public:
    ScopeLog(std::string label) {
        name = label;
        std::cout << "enter=" << name << std::endl;
    }

    ~ScopeLog() {
        std::cout << "leave=" << name << std::endl;
    }
};

int runJob(std::string label, int workUnits) {
    ScopeLog scope(label);
    int total = 0;
    for (int i = 1; i <= workUnits; i++) {
        total += i;
    }
    return total;
}

int main() {
    std::string label = "load";
    int workUnits = 5;

    int total = runJob(label, workUnits);

    std::cout << "total=" << total << std::endl;
    return 0;
}

                        
1label ← load, workUnits ← 3⋯28int main() {29    std::string label→ load = "load"; //@label="save", "sync"30    int workUnits→ 3 = 3; //@workUnits=1, 53132    int total = runJob(labelload, workUnits3);⋯
2int runJob(std::string label, int workUnits)⋯19int runJob(std::string labelload, int workUnits3) {20    ScopeLog scope(labelload);21    int total = 0;⋯
3ScopeLog(std::string label)⋯8public:9    ScopeLog(std::string labelload) {10        name = labelload;11        std::cout << "enter=" << name << std::endl;12    }⋯outputenter=load
4scope ← (empty), total ← 0⋯19int runJob(std::string label, int workUnits) {20    ScopeLog scope→ (empty)(labelload);21    int total→ 0 = 0;22    for (int i = 1; i <= workUnits; i++) {⋯
5total ← 1pass 1 of 3⋯21int total = 0;22for (int i1 = 1; i <= workUnits3; i++) {23    total→ 1 += i1;24}⋯All 3 passes — pass 1 is the card abovepassitotal
110 → 1
221 → 3
333 → 6
6return total;⋯24    }25    return total6;26}⋯
7~ScopeLog()⋯14~ScopeLog() {15    std::cout << "leave=" << name << std::endl;16}⋯outputleave=load
8total ← 6⋯32    int total→ 6 = runJob(labelload, workUnits3);3334    std::cout << "total=" << total6 << std::endl;35    return 0;36}⋯outputtotal=6
1label ← save, workUnits ← 3⋯28int main() {29    std::string label→ save = "save";30    int workUnits→ 3 = 3;3132    int total = runJob(labelsave, workUnits3);⋯
2int runJob(std::string label, int workUnits)⋯19int runJob(std::string labelsave, int workUnits3) {20    ScopeLog scope(labelsave);21    int total = 0;⋯
3ScopeLog(std::string label)⋯8public:9    ScopeLog(std::string labelsave) {10        name = labelsave;11        std::cout << "enter=" << name << std::endl;12    }⋯outputenter=save
4scope ← (empty), total ← 0⋯19int runJob(std::string label, int workUnits) {20    ScopeLog scope→ (empty)(labelsave);21    int total→ 0 = 0;22    for (int i = 1; i <= workUnits; i++) {⋯
5total ← 1pass 1 of 3⋯21int total = 0;22for (int i1 = 1; i <= workUnits3; i++) {23    total→ 1 += i1;24}⋯All 3 passes — pass 1 is the card abovepassitotal
110 → 1
221 → 3
333 → 6
6return total;⋯24    }25    return total6;26}⋯
7~ScopeLog()⋯14~ScopeLog() {15    std::cout << "leave=" << name << std::endl;16}⋯outputleave=save
8total ← 6⋯32    int total→ 6 = runJob(labelsave, workUnits3);3334    std::cout << "total=" << total6 << std::endl;35    return 0;36}⋯outputtotal=6
1label ← sync, workUnits ← 3⋯28int main() {29    std::string label→ sync = "sync";30    int workUnits→ 3 = 3;3132    int total = runJob(labelsync, workUnits3);⋯
2int runJob(std::string label, int workUnits)⋯19int runJob(std::string labelsync, int workUnits3) {20    ScopeLog scope(labelsync);21    int total = 0;⋯
3ScopeLog(std::string label)⋯8public:9    ScopeLog(std::string labelsync) {10        name = labelsync;11        std::cout << "enter=" << name << std::endl;12    }⋯outputenter=sync
4scope ← (empty), total ← 0⋯19int runJob(std::string label, int workUnits) {20    ScopeLog scope→ (empty)(labelsync);21    int total→ 0 = 0;22    for (int i = 1; i <= workUnits; i++) {⋯
5total ← 1pass 1 of 3⋯21int total = 0;22for (int i1 = 1; i <= workUnits3; i++) {23    total→ 1 += i1;24}⋯All 3 passes — pass 1 is the card abovepassitotal
110 → 1
221 → 3
333 → 6
6return total;⋯24    }25    return total6;26}⋯
7~ScopeLog()⋯14~ScopeLog() {15    std::cout << "leave=" << name << std::endl;16}⋯outputleave=sync
8total ← 6⋯32    int total→ 6 = runJob(labelsync, workUnits3);3334    std::cout << "total=" << total6 << std::endl;35    return 0;36}⋯outputtotal=6
1label ← load, workUnits ← 1⋯28int main() {29    std::string label→ load = "load";30    int workUnits→ 1 = 1;3132    int total = runJob(labelload, workUnits1);⋯
2int runJob(std::string label, int workUnits)⋯19int runJob(std::string labelload, int workUnits1) {20    ScopeLog scope(labelload);21    int total = 0;⋯
3ScopeLog(std::string label)⋯8public:9    ScopeLog(std::string labelload) {10        name = labelload;11        std::cout << "enter=" << name << std::endl;12    }⋯outputenter=load
4scope ← (empty), total ← 0⋯19int runJob(std::string label, int workUnits) {20    ScopeLog scope→ (empty)(labelload);21    int total→ 0 = 0;22    for (int i = 1; i <= workUnits; i++) {⋯
5total ← 1⋯21int total = 0;22for (int i1 = 1; i <= workUnits1; i++) {23    total→ 1 += i1;24}⋯
6return total;⋯24    }25    return total1;26}⋯
7~ScopeLog()⋯14~ScopeLog() {15    std::cout << "leave=" << name << std::endl;16}⋯outputleave=load
8total ← 1⋯32    int total→ 1 = runJob(labelload, workUnits1);3334    std::cout << "total=" << total1 << std::endl;35    return 0;36}⋯outputtotal=1
1label ← load, workUnits ← 5⋯28int main() {29    std::string label→ load = "load";30    int workUnits→ 5 = 5;3132    int total = runJob(labelload, workUnits5);⋯
2int runJob(std::string label, int workUnits)⋯19int runJob(std::string labelload, int workUnits5) {20    ScopeLog scope(labelload);21    int total = 0;⋯
3ScopeLog(std::string label)⋯8public:9    ScopeLog(std::string labelload) {10        name = labelload;11        std::cout << "enter=" << name << std::endl;12    }⋯outputenter=load
4scope ← (empty), total ← 0⋯19int runJob(std::string label, int workUnits) {20    ScopeLog scope→ (empty)(labelload);21    int total→ 0 = 0;22    for (int i = 1; i <= workUnits; i++) {⋯
5total ← 1pass 1 of 5⋯21int total = 0;22for (int i1 = 1; i <= workUnits5; i++) {23    total→ 1 += i1;24}⋯All 5 passes — pass 1 is the card abovepassitotal
110 → 1
221 → 3
333 → 6
446 → 10
5510 → 15
6return total;⋯24    }25    return total15;26}⋯
7~ScopeLog()⋯14~ScopeLog() {15    std::cout << "leave=" << name << std::endl;16}⋯outputleave=load
8total ← 15⋯32    int total→ 15 = runJob(labelload, workUnits5);3334    std::cout << "total=" << total15 << std::endl;35    return 0;36}⋯outputtotal=15
All 3 passes — pass 1 is the card above
pass	`i`	`total`
1	1	0 → 1
2	2	1 → 3
3	3	3 → 6
All 3 passes — pass 1 is the card above
pass	`i`	`total`
1	1	0 → 1
2	2	1 → 3
3	3	3 → 6
All 3 passes — pass 1 is the card above
pass	`i`	`total`
1	1	0 → 1
2	2	1 → 3
3	3	3 → 6
All 5 passes — pass 1 is the card above
pass	`i`	`total`
1	1	0 → 1
2	2	1 → 3
3	3	3 → 6
4	4	6 → 10
5	5	10 → 15
Enter, Work, Leave

runJob creates ScopeLog scope(label).
The constructor prints enter=load.
The loop adds work units into total.
Leaving runJob destroys scope.
The destructor prints leave=load automatically. | Moment | What happens | | --- | --- | | enter scope | acquire/log load | | inside scope | calculate 1 + 2 + 3 | | leave scope | release/log load |
Exercise: raii_scope.cpp

Create a scope logger that prints on entry and exit while a small job computes a total