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Diffstat (limited to 'build2/context.hxx')
| -rw-r--r-- | build2/context.hxx | 399 |
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diff --git a/build2/context.hxx b/build2/context.hxx new file mode 100644 index 0000000..ff8b5b3 --- /dev/null +++ b/build2/context.hxx @@ -0,0 +1,399 @@ +// file : build2/context.hxx -*- C++ -*- +// copyright : Copyright (c) 2014-2017 Code Synthesis Ltd +// license : MIT; see accompanying LICENSE file + +#ifndef BUILD2_CONTEXT_HXX +#define BUILD2_CONTEXT_HXX + +#include <build2/types.hxx> +#include <build2/utility.hxx> + +#include <build2/scope.hxx> +#include <build2/variable.hxx> +#include <build2/operation.hxx> +#include <build2/scheduler.hxx> + +namespace build2 +{ + // Main (and only) scheduler. Started up and shut down in main(). + // + extern scheduler sched; + + // In order to perform each operation the build system goes through the + // following phases: + // + // load - load the buildfiles + // match - search prerequisites and match rules + // execute - execute the matched rule + // + // The build system starts with a "serial load" phase and then continues + // with parallel search and execute. Match, however, can be interrupted + // both with load and execute. + // + // Match can be interrupted with "exclusive load" in order to load + // additional buildfiles. Similarly, it can be interrupted with (parallel) + // execute in order to build targetd required to complete the match (for + // example, generated source code or source code generators themselves. + // + // Such interruptions are performed by phase change that is protected by + // phase_mutex (which is also used to synchronize the state changes between + // phases). + // + // Serial load can perform arbitrary changes to the model. Exclusive load, + // however, can only perform "island appends". That is, it can create new + // "nodes" (variables, scopes, etc) but not change already existing nodes or + // invalidate any references to such (the idea here is that one should be + // able to load additional buildfiles as long as they don't interfere with + // the existing build state). The "islands" are identified by the + // load_generation number (0 for initial/serial load). It is incremented in + // case of a phase switch and is stored in various "nodes" (variables, etc) + // to allow modifications "within the islands". + // + extern run_phase phase; + extern size_t load_generation; + + // A "tri-mutex" that keeps all the threads in one of the three phases. When + // a thread wants to switch a phase, it has to wait for all the other + // threads to do the same (or release their phase locks). The load phase is + // exclusive. + // + // The interleaving match and execute is interesting: during match we read + // the "external state" (e.g., filesystem entries, modifications times, etc) + // and capture it in the "internal state" (our dependency graph). During + // execute we are modifying the external state with controlled modifications + // of the internal state to reflect the changes (e.g., update mtimes). If + // you think about it, it's pretty clear that we cannot safely perform both + // of these actions simultaneously. A good example would be running a code + // generator and header dependency extraction simultaneously: the extraction + // process may pick up headers as they are being generated. As a result, we + // either have everyone treat the external state as read-only or write-only. + // + class phase_mutex + { + public: + // Acquire a phase lock potentially blocking (unless already in the + // desired phase) until switching to the desired phase is possible. + // + void + lock (run_phase); + + // Release the phase lock potentially allowing (unless there are other + // locks on this phase) switching to a different phase. + // + void + unlock (run_phase); + + // Switch from one phase to another. Semantically, just unlock() followed + // by lock() but more efficient. + // + void + relock (run_phase unlock, run_phase lock); + + private: + friend struct phase_lock; + friend struct phase_unlock; + friend struct phase_switch; + + phase_mutex (): lc_ (0), mc_ (0), ec_ (0) {phase = run_phase::load;} + + static phase_mutex instance; + + private: + // We have a counter for each phase which represents the number of threads + // in or waiting for this phase. + // + // We use condition variables to wait for a phase switch. The load phase + // is exclusive so we have a separate mutex to serialize it (think of it + // as a second level locking). + // + // When the mutex is unlocked (all three counters become zero, the phase + // is always changed to load (this is also the initial state). + // + mutex m_; + size_t lc_; + size_t mc_; + size_t ec_; + + condition_variable lv_; + condition_variable mv_; + condition_variable ev_; + + mutex lm_; + }; + + // Grab a new phase lock releasing it on destruction. The lock can be + // "owning" or "referencing" (recursive). + // + // On the referencing semantics: If there is already an instance of + // phase_lock in this thread, then the new instance simply references it. + // + // The reason for this semantics is to support the following scheduling + // pattern (in actual code we use wait_guard to RAII it): + // + // atomic_count task_count (0); + // + // { + // phase_lock l (run_phase::match); // (1) + // + // for (...) + // { + // sched.async (task_count, + // [] (...) + // { + // phase_lock pl (run_phase::match); // (2) + // ... + // }, + // ...); + // } + // } + // + // sched.wait (task_count); // (3) + // + // Here is what's going on here: + // + // 1. We first get a phase lock "for ourselves" since after the first + // iteration of the loop, things may become asynchronous (including + // attempts to switch the phase and modify the structure we are iteration + // upon). + // + // 2. The task can be queued or it can be executed synchronously inside + // async() (refer to the scheduler class for details on this semantics). + // + // If this is an async()-synchronous execution, then the task will create + // a referencing phase_lock. If, however, this is a queued execution + // (including wait()-synchronous), then the task will create a top-level + // phase_lock. + // + // Note that we only acquire the lock once the task starts executing + // (there is no reason to hold the lock while the task is sitting in the + // queue). This optimization assumes that whatever else we pass to the + // task (for example, a reference to a target) is stable (in other words, + // such a reference cannot become invalid). + // + // 3. Before calling wait(), we release our phase lock to allow switching + // the phase. + // + struct phase_lock + { + explicit phase_lock (run_phase); + ~phase_lock (); + + phase_lock (phase_lock&&) = delete; + phase_lock (const phase_lock&) = delete; + + phase_lock& operator= (phase_lock&&) = delete; + phase_lock& operator= (const phase_lock&) = delete; + + run_phase p; + + static +#ifdef __cpp_thread_local + thread_local +#else + __thread +#endif + phase_lock* instance; + }; + + // Assuming we have a lock on the current phase, temporarily release it + // and reacquire on destruction. + // + struct phase_unlock + { + phase_unlock (bool unlock = true); + ~phase_unlock (); + + phase_lock* l; + }; + + // Assuming we have a lock on the current phase, temporarily switch to a + // new phase and switch back on destruction. + // + struct phase_switch + { + explicit phase_switch (run_phase); + ~phase_switch (); + + run_phase o, n; + }; + + // Wait for a task count optionally and temporarily unlocking the phase. + // + struct wait_guard + { + ~wait_guard () noexcept (false); + + explicit + wait_guard (atomic_count& task_count, + bool phase = false); + + wait_guard (size_t start_count, + atomic_count& task_count, + bool phase = false); + + void + wait (); + + size_t start_count; + atomic_count* task_count; + bool phase; + }; + + // Cached variables. + // + extern const variable* var_src_root; + extern const variable* var_out_root; + extern const variable* var_src_base; + extern const variable* var_out_base; + + extern const variable* var_project; + extern const variable* var_amalgamation; + extern const variable* var_subprojects; + + extern const variable* var_import_target; // import.target + + // Current action (meta/operation). + // + // The names unlike info are available during boot but may not yet be + // lifted. The name is always for an outer operation (or meta operation + // that hasn't been recognized as such yet). + // + extern const string* current_mname; + extern const string* current_oname; + + extern const meta_operation_info* current_mif; + extern const operation_info* current_inner_oif; + extern const operation_info* current_outer_oif; + extern size_t current_on; // Current operation number (1-based) in the + // meta-operation batch. + + extern execution_mode current_mode; + + // Total number of dependency relationships in the current action. Together + // with the target::dependents count it is incremented during the rule + // search & match phase and is decremented during execution with the + // expectation of it reaching 0. Used as a sanity check. + // + extern atomic_count dependency_count; + + inline void + set_current_mif (const meta_operation_info& mif) + { + current_mname = &mif.name; + current_mif = &mif; + current_on = 0; // Reset. + } + + inline void + set_current_oif (const operation_info& inner_oif, + const operation_info* outer_oif = nullptr) + { + current_oname = &(outer_oif == nullptr ? inner_oif : *outer_oif).name; + current_inner_oif = &inner_oif; + current_outer_oif = outer_oif; + current_on++; + current_mode = inner_oif.mode; + dependency_count.store (0, memory_order_relaxed); // Serial. + } + + // Keep going flag. + // + // Note that setting it to false is not of much help unless we are running + // serially. In parallel we queue most of the things up before we see any + // failures. + // + extern bool keep_going; + + // Reset the build state. In particular, this removes all the targets, + // scopes, and variables. + // + variable_overrides + reset (const strings& cmd_vars); + + // Return the project name or empty string if unnamed. + // + inline const string& + project (const scope& root) + { + auto l (root[var_project]); + return l ? cast<string> (l) : empty_string; + } + + // Return the src/out directory corresponding to the given out/src. The + // passed directory should be a sub-directory of out/src_root. + // + dir_path + src_out (const dir_path& out, const scope& root); + + dir_path + src_out (const dir_path& out, + const dir_path& out_root, const dir_path& src_root); + + dir_path + out_src (const dir_path& src, const scope& root); + + dir_path + out_src (const dir_path& src, + const dir_path& out_root, const dir_path& src_root); + + // Action phrases, e.g., "configure update exe{foo}", "updating exe{foo}", + // and "updating exe{foo} is configured". Use like this: + // + // info << "while " << diag_doing (a, t); + // + class target; + + struct diag_phrase + { + const action& a; + const target& t; + void (*f) (ostream&, const action&, const target&); + }; + + inline ostream& + operator<< (ostream& os, const diag_phrase& p) + { + p.f (os, p.a, p.t); + return os; + } + + void + diag_do (ostream&, const action&, const target&); + + inline diag_phrase + diag_do (const action& a, const target& t) + { + return diag_phrase {a, t, &diag_do}; + } + + void + diag_doing (ostream&, const action&, const target&); + + inline diag_phrase + diag_doing (const action& a, const target& t) + { + return diag_phrase {a, t, &diag_doing}; + } + + void + diag_did (ostream&, const action&, const target&); + + inline diag_phrase + diag_did (const action& a, const target& t) + { + return diag_phrase {a, t, &diag_did}; + } + + void + diag_done (ostream&, const action&, const target&); + + inline diag_phrase + diag_done (const action& a, const target& t) + { + return diag_phrase {a, t, &diag_done}; + } +} + +#include <build2/context.ixx> + +#endif // BUILD2_CONTEXT_HXX |